C/H expansion tank is hot!
David J
with the water through the radiators. I found a key and bled the
downstairs rads. Upstairs the rads were lukewarm, and one was full of
air. I then heard an overflow happening from the loft tanks.
I climbed into the loft to investigate, and found that the DHW header
was OK. However the C/H header was full of dirty water which was quite
hot and overflowing the tank. The ballcock was half submerged.
I immediately turned off the pump, and rang the plumber who had
installed a new pump in October. I assume that he checked the system
before he left the property. He cannot visit until next week sometime,
but said there must be a 'blockage' causing the overflow of C/H water
into the expansion tank. He told me to isolate all the upstairs rads,
and just run on the downstairs rads.
I have no idea how the upstairs & downstairs piping runs are
configured, but found the situation so scary that I have left the pump
off for now. This is a 1950s ex-council house with a back boiler gas
fired C/H system, possibly added after the original build.
Any ideas what might have happened here?
David
...
> Visiting a friend today,
Female friend by any chance?
Tim W
wibbled on Saturday 05 December 2009 21:59
I might be missing something but it's quite normal for the CH water to flow
back into the expansion tank - that's why it's called and expansion tank ;->
Now, if there was lots of air trapped, then air expands more than water when
it gets hot, so assuming some of the air got hot, it may have caused the
expansion tank to actually overflow to the drain/outside overflow.
Under normal conditions, the water level will rise and fall within the tank.
When it rises, it may do so with normally hot (not boiling) water. The
ballcock should be set (arm bent usually) to fill the tank enough to cover
the outlet to the CH. When the system heats, the water level will rise
(typically a few litres) but will not overflow if the ballcock has been set
right.
Did the plumber drain and refill the system when he changed the pump?
Usually this is not necessary if the pump isolator valves are working, but
either they weren't or he wanted to clean out and refill the system, perhaps
with fresh inhibitor. If so, then even if the system is bled, it may need
rebleeding later as dissolve air comes out of the new water.
On the face of it, it really doesn't sound that bad. If the water is rising
and falling in the tank, it is not about to blow up. If the overflow is
working then there shouldn't be any danger in running the system.
Can you continue to bleed the air out of all the rads and run normally?
I would bet that after the last of the air is gone that the tank will no
longer overflow, but that the water level will rise and fall withing the
confines of the tank. It is perfectly normal for the ball to be fairly
submerged as it should be set low anyway as I mentioned above.
On an aside, if the water is dirty looking, it sounds like there *may* be a
lack of inhibitor which should prevent iron oxide formation from the rads.
Having said that, CH water doesn't always look too clean even with
chemicals...
HTH
Tim
--
Tim Watts
This space intentionally left blank...
Roger Mills
David J <da...@btelecom.invalid> wrote:
Has this problem only started since the pump was changed, or has it always
been like it?
*Why* was the pump changed?
Sounds to me like it's either pumping over (is water flowing out of the vent
pipe back into the tank?) or it's sucking air through the vent pipe. If it's
a new problem, either the pump is set at too high a speed, or it's fitted
the wrong way round - and pumping in the wrong direction.
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!
David J
Hi thanks for prompt answers here.
Lots of questions from Tim & Roger. And yes it is a lady!
1. Pump was changed recently because it was knackered and was making
knocking noise. (It had been doing so slightly for the past 2 heating
seasons, but my advice to get it changed was ignored!)
While I was away on holiday it got seriously loud, so a local plumber
was called in. As I was not around I have no idea if he totally
drained the system. He probably did because the old pump had corroded
isolating valves which have now been renewed.
He certainly did not add Fernox or any inhibitor.
2. The pump maybe is set at too high a speed. I can reduce that and
see what difference it makes.
3. It isn't fitted the wrong way round. It has been working OK for the
past month or so.
4. I cannot believe that the header tank (that is the expansion tank
-right?) should ever be warm. The one in my own house is always cold,
and at a steady level. The hot water must have come from the overhead
pipe which is the expansion line. And then the surplus overflowed via
the overflow pipe to outdoors.
5. Just before I left the house I also noticed another fault. The hall
(the only one) thermostat is NOT controlling the pump. It clicks at
the ambient temp, but the pump is not inhibited when the temp setting
is reduced.
I am now wondering if this C/H system is simply over-heating and is
relying on the programmable timer to not loose more water from the
system.
I did successfully bleed one upstairs rad with the usual key. Masses
of air in there. But 2 others need a large screwdriver to effect the
bleeding. When did those radiators stop being used?
David
Andrew Gabriel
David J <da...@btelecom.invalid> writes:
> Hi thanks for prompt answers here.
>
> Lots of questions from Tim & Roger. And yes it is a lady!
>
> 1. Pump was changed recently because it was knackered and was making
> knocking noise. (It had been doing so slightly for the past 2 heating
> seasons, but my advice to get it changed was ignored!)
>
> While I was away on holiday it got seriously loud, so a local plumber
> was called in. As I was not around I have no idea if he totally
> drained the system. He probably did because the old pump had corroded
> isolating valves which have now been renewed.
>
> He certainly did not add Fernox or any inhibitor.
How do you know?
> 2. The pump maybe is set at too high a speed. I can reduce that and
> see what difference it makes.
Could end up with insufficient flow throug hthe boiler.
> 3. It isn't fitted the wrong way round. It has been working OK for the
> past month or so.
>
> 4. I cannot believe that the header tank (that is the expansion tank
> -right?) should ever be warm. The one in my own house is always cold,
> and at a steady level. The hot water must have come from the overhead
> pipe which is the expansion line. And then the surplus overflowed via
> the overflow pipe to outdoors.
The clue is in the name _expansion_ tank. As the water in the heating
system is heated, it expands back up into the _expansion_ tank, and
yes, that will be warm, or it wouldn't have expanded.
> 5. Just before I left the house I also noticed another fault. The hall
> (the only one) thermostat is NOT controlling the pump. It clicks at
> the ambient temp, but the pump is not inhibited when the temp setting
> is reduced.
Pump is probably controlled by the boiler, and it will likely leave
it running for up to a couple of minutes after it stopped firing.
Overflowing the expansion tank could be because there's insufficient
clearance between the fill level and the overflow to allow the water
to expand without overflowing, or it could be because there's a leak
between the hot water system and the central heating system, which
is usually in the coil in the hot water cylinder. If the level doesn't
drop back to normal and stay there when the heating system is cold,
then it's the latter (holed coil in hot water cylinder).
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
David J
I don't know about the maths and the volume of water in the system
that has to expand when it is hot - but there is a length of vertical
expansion pipework before the header tank. Surely the water expansion
will mostly take place in there?
About the idea of a hole in the coil. Would this not make the
domestic hot water as dirty as the radiator water?
David
David J
wrote:
After further thoughts, please disregard the above comment!
John Rumm
> About the idea of a hole in the coil. Would this not make the
> domestic hot water as dirty as the radiator water?
No, because the main header tank is higher than the CH header usually -
so the water in the cylinder is at slightly higher pressure than that in
the coil. So fresh water enters the heating circuit, rather than the
other way round,
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
David J
<see.my.s...@nowhere.null> wrote:
>David J wrote:
>
>> About the idea of a hole in the coil. Would this not make the
>> domestic hot water as dirty as the radiator water?
>
>No, because the main header tank is higher than the CH header usually -
>so the water in the cylinder is at slightly higher pressure than that in
>the coil. So fresh water enters the heating circuit, rather than the
>other way round,
OK John, thanks for that info.
Going to revisit the problem this morning and look again with a 'cold'
start before I switch the pump on again. I'll take a infrared
thermometer along to see how the radiators heat up.
I'll see what the pump speed is currently set at, and I'll look into
the C/H expansion tank and see how that has settled down overnight.
I'll use a big screwdriver and bleed the two odd radiators upstairs.
I'm pretty sure they are full of air.
I'll set the hall thermostat at min, and leave it there initially. The
C/H should not start at that setting, I know. If it does then the
wiring to the new programmer need attention, I would think.
I'll report back how it all works out.....
David
Tim W
wibbled on Sunday 06 December 2009 01:13
> I don't know about the maths and the volume of water in the system
> that has to expand when it is hot -
The maths is easy - there are net expansion calculators on the web, or use
the expansion coefficient of water (this varies by temp, but it's good
enough to stab an average value in and see what the expansion is between say
15C and 80C. The harder bit is estimating the volume of the rads and pipe.
> but there is a length of vertical
> expansion pipework before the header tank. Surely the water expansion
> will mostly take place in there?
Nowhere near. That pipe will be "full" to the same level as water in the
tank. You'll get a good "couple" (+/-) of litres expansion out of a typical
system depending on volume of system.
Harry Bloomfield
> 4. I cannot believe that the header tank (that is the expansion tank
> -right?) should ever be warm. The one in my own house is always cold,
> and at a steady level. The hot water must have come from the overhead
> pipe which is the expansion line. And then the surplus overflowed via
> the overflow pipe to outdoors.
You are correct, it should certainly not be warm. Warm can cause moist
air in the loft space helping to rot roof timbers. The tank is just
there to allow some expansion, to keep the system topped up and to
provide a steady pressure or head of water in the system.
I would suggest trying bleeding the system with the pump turned off, so
that there is no chance of the pump causing negative pressure and
sucking yet more air in rather than it being bled out. Once the
majority of the air is bled out, then watch what is happening in the
tank with pump running - first with system cold, then with it heating
up.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
Harry Bloomfield
> Nowhere near. That pipe will be "full" to the same level as water in the
> tank. You'll get a good "couple" (+/-) of litres expansion out of a typical
> system depending on volume of system.
Much of which I would expect to be accommodated by the pipework on its
way upto the tank and once the system has heated up, there should be no
more expansion - hence little heat rising into the tank.
Dave Liquorice
>> Nowhere near. That pipe will be "full" to the same level as water
in
>> the tank. You'll get a good "couple" (+/-) of litres expansion out
of a
>> typical system depending on volume of system.
>
> Much of which I would expect to be accommodated by the pipework on its
> way upto the tank
No, think about it. The water in the vent pipe is connected directly
to the feed pipe via the system. Water finds it's level, so the water
level in the vent pipe is the same as that in the tank.
When the system starts heating up the water expands and that increase
in volume is accomodated by water moving up the feed pipe into the
tank. Raising the level in the tank and thus in the vent pipe but
that is only a inch or so of pipe so not a significant volume
compared to raising the level in the tank by and inch or so.
> ... and once the system has heated up, there should be no more expansion
> - hence little heat rising into the tank.
Correct. At worst the tank should only get a little warm. Hot is bad
so is any flow from the vent pipe, even a regular drip or a short
dribble when the pump starts.
--
Cheers
Dave.
Roger Mills
>
> I would suggest trying bleeding the system with the pump turned off,
> so that there is no chance of the pump causing negative pressure and
> sucking yet more air in rather than it being bled out. Once the
> majority of the air is bled out, then watch what is happening in the
> tank with pump running - first with system cold, then with it heating
> up.
It's also worth checking that it *is* air which is in the radiators. It
there's no inhibitor in the system, it could be hydrogen caused by
corrosion. If what comes out of the bleed hole burns with a blue flame when
you stick a match to it, it's hydrogen!
Is there a lot of black sludge in the bottom of the F&E tank? This would be
another indicator of corrosion. If hydrogen *is* being produced, and is
collecting in the radiators, it will be displacing the water - and could
account for the rise in level in the F&E tank.
Graham.
>
> 5. Just before I left the house I also noticed another fault. The hall
> (the only one) thermostat is NOT controlling the pump. It clicks at
> the ambient temp, but the pump is not inhibited when the temp setting
> is reduced.
If your system is fully pumped, and the DHW cylinder was still calling
for heat, the stat would have merely closed the motorised valve on the CH side
leaving the pump running to supply the DHW.
--
Graham.
%Profound_observation%
cynic
Back boiler - probably gravity hot water and pumped central heating.
At a guess there could be a hole in the primary coil of the hot water
cylinder. Is the hot tap water supply tank ball float valve
continuously filling?
The continuous introduction of fresh water with dissolved air in it
will cause corrosion as well as the air coming out of solution when
the temperature rises and being noisily pumped round the pipework.
Dave Baker
"David J" <da...@btelecom.invalid> wrote in message
news:htmmh5p2k8v0oaqoc...@4ax.com...
Hi David,
There are several possibilities for this problem and it's easy to work out
which is the cause. I've suffered from all of them on my own system at one
time or another.
1) Holed coil in the immersion tank. With the heating and hot water switched
off this problem will still manifest as the water levels in both of the loft
tanks trying to equalise. The level in the large cold water supply tank is
usually higher than that in the small heating system supply tank and often
the CW overflow goes into the HS supply tank and thence to the outside via
that tank's overflow. If the HS tank is overflowing with no obvious inflow
from the ballcock or the CW overflow pipe then a holed coil is present. Only
clean water should enter the HS tank though.
2) Pumping over. If the boiler pump is at too high a setting or fitted the
wrong way round, or indeed if the pipework has been badly planned so the
vent pipes are on the pressure side of the pump, then the immersion tank or
boiler vent pipes can pump over into the HS supply tank. However this should
not cause the tank to overflow because no additional water should be
entering the system. The overpumped water just finds its way back into the
circuit again via the tank and keeps circulating. However the HS tank will
of course get hot.
3) Ballcock set too high. The HS tank needs some room for expansion as the
water in the system heats up. Usually you set it at about half the height of
the tank and the ballcock will end up somewhat submerged. If the level is
too high the tank starts to overflow as the water expands into it however it
should then stop overflowing as equilibrium is achieved and the water in the
tank should not get hot.
To those who suggested that expansion might cause the vent pipe to overflow
into the HS tank, that I'm afraid is just silly. The water in the vent pipe
and HS tank will always be at the same level because they're both open to
atmosphere i.e at the absolute most this will be the level of the HS tank
overflow pipe. Only if pumping over is occuring can water come out of the
vent pipe.
So the most likely cause of both an overflow plus hot water in the HS tank
is pumping over which will obviously only manifest with the boiler running.
By seeing what happens with the boiler both off and on you should be able to
determine the cause.
FWIW when my own system started pumping over and it couldn't be cured by
reducing the pump setting I just capped the immersion tank vent pipe off
with an old radiator valve. Expansion, how my system was arranged at least,
could occur just as happily back up into the HS tank via its outlet pipe and
the vent pipe was actually redundant. I fact I can't envisage a system which
actually really needs a vent pipe although I'm sure that will lead to a
storm of protest.
Finally when my immersion tank sprang a hole in the coil and while I was
still in shock at the cost of a new one a lorry turned up with a brand new
tank on it which someone else had ordered and misdelivered it to my house
(or at least they left it with a neighbour because I was out). I never did
find out who it was really meant for but was grateful to the plumbing gods
for such a timely intervention.
--
Dave Baker
David J
Thanks everyone for all the follow-up suggestions. However this
morning's checks have revealed something unexpected.
I re-checked the new pump fitted in October. It is a DAB EVO VA55/130
with 3 settings. This one was set to 3, the 70W setting (the largest).
Too high, I thought.
This pump is available for about �25, I note, so it's not the best on
the market.
I then re-checked the fitting direction of the arrows on the casing,
and I'm pretty convinced that is (as Roger suggested yesterday) fitted
the WRONG WAY around.
The arrows are facing downwards. That is the direction of the boiler.
Upwards is the direction of the hot water cylinder.
As I understand it, this will put pressure on the pipe to the boiler
(and to the expansion pipe at the C/H header tank) and suction on the
pipe to the cylinder. Please tell me if I am wrong here.
I decided to leave the pump switched off. I bled the 2 other upstairs
rads & both were full of air.
This wrong pump configuration will surely explain:
1. excessive air in the upstairs C/H radiators.
2. some hot water being returned up the expansion pipe, and occasional
overflowing of the header tank via the pipe provided. And the water in
the header tank being dirty.
3. The C/H system 'working', but only just.
I will discuss all this with the plumber when/if he shows up tomorrow.
The electrics & the thermostat are something else. His mate, an
electrician, connected that up.
David
Roger Mills
>
> I then re-checked the fitting direction of the arrows on the casing,
> and I'm pretty convinced that is (as Roger suggested yesterday) fitted
> the WRONG WAY around.
>
> The arrows are facing downwards. That is the direction of the boiler.
> Upwards is the direction of the hot water cylinder.
>
Is it a fully pumped system, or is it - as someone has suggested - a gravity
HW and pumped CH system? If the latter, it's not unusual to have the pump in
the return leg.
How many water pipes connect to the boiler? Where are the vent and fill
pipes connected into the circulatory pipework? If you could draw a diagram
of the system and upload it somewhere, with a link posted here, it would be
a great help.
David J
<watt....@googlemail.com> wrote:
>In an earlier contribution to this discussion,
>David J <da...@btelecom.invalid> wrote:
>
>>
>> I then re-checked the fitting direction of the arrows on the casing,
>> and I'm pretty convinced that is (as Roger suggested yesterday) fitted
>> the WRONG WAY around.
>>
>> The arrows are facing downwards. That is the direction of the boiler.
>> Upwards is the direction of the hot water cylinder.
>>
>
>Is it a fully pumped system, or is it - as someone has suggested - a gravity
>HW and pumped CH system? If the latter, it's not unusual to have the pump in
>the return leg.
>
>How many water pipes connect to the boiler? Where are the vent and fill
>pipes connected into the circulatory pipework? If you could draw a diagram
>of the system and upload it somewhere, with a link posted here, it would be
>a great help.
I am pretty sure that it is, as Cynic suggested, a gravity hot water
system with a pumped C/H system. There is also an enclosed gas fire
in the lounge on the same unit.
It is all very primitive. I checked in the airing cupboard to see what
is hanging off the cylinder, and there is no 3-way motorised valve,
just pipe connections. No immersion heater back-up either!
Why I initially dismisseed the idea that the pump was in backwards,
was that it was installed by a regular plumber - not a general
handyman (no offence TMH!)
The C/H header tank has now returned to its normal levels after my
pump switch-off, plus the additional rad bleeding done this morning.
But there are signs on the end of the overflow pipe sitting over the
tank that there have been recent flows.
If I get nowhere with the plumber I will do a sketch of the overall
system, as you suggested.
Thinking about it, surely the pump is currently in the 'return leg',
but facing the wrong way?
David
Tim W
wibbled on Sunday 06 December 2009 09:52
> Tim W formulated the question :
>> Nowhere near. That pipe will be "full" to the same level as water in the
>> tank. You'll get a good "couple" (+/-) of litres expansion out of a
>> typical system depending on volume of system.
>
> Much of which I would expect to be accommodated by the pipework on its
> way upto the tank and once the system has heated up, there should be no
> more expansion - hence little heat rising into the tank.
>
>
That would be hard as the pipe to the tank is full even when cold. To do
what you propose would require a magic ballcock that cut off when the water
was several feet down the pipe below the base of the tank!
cynic
>
> - Show quoted text -
Your comment about an overflow pipe sitting over the tank concerns me.
I have occasionally found such a set up where the overflow from the
higher tank discharges into the lower tank but it is incorrect.
However if this is the case and the higher tank serves the domestic
hot water then if the ball-float valve is worn it can let a
significant amount of water by overnight when demand on the mains is
low and the pressure is high. Any watert hus passing into the heating
feed and expansion tank will contain dissolved air and could create
some of your problem. It will certainly lead to corosion and sludge
creation!
As others have said older systems sometimes had the pump in the return
leg from the radiators thus creating a slight suction on the rad
system, leading to air being drawn in through old or weak joints. If
the pump is in the flow pipe and pushing water away from the boiler it
will tend to pressurise the system and the air entrainment will not
occur.
We must wait for your diagram with interest
Roger Mills
David J <da...@btelecom.invalid> wrote:
>
>
> I am pretty sure that it is, as Cynic suggested, a gravity hot water
> system with a pumped C/H system. There is also an enclosed gas fire
> in the lounge on the same unit.
>
Most likely a Baxi Bermuda.
> It is all very primitive. I checked in the airing cupboard to see what
> is hanging off the cylinder, and there is no 3-way motorised valve,
> just pipe connections. No immersion heater back-up either!
>
If it's gravity HW, there won't usually be any motorised valves - the HW
circuit works by convection whenever the boiler is firing, and the CH only
works when the pump is turned on. But I *still* want to know how the fill
and vent pipes are connected. I have drawn a very crude diagram of typical
setup, which you can find at http://www.mills37.plus.com/Heating.pdf That
shows what I believe to be the usual way of connecting the fill and vent
pipes - into the gravity circuit in the airing cupboard. Is the system in
question like that? If not, what *is* it like?
> Why I initially dismisseed the idea that the pump was in backwards,
> was that it was installed by a regular plumber - not a general
> handyman (no offence TMH!)
>
> The C/H header tank has now returned to its normal levels after my
> pump switch-off, plus the additional rad bleeding done this morning.
> But there are signs on the end of the overflow pipe sitting over the
> tank that there have been recent flows.
>
> If I get nowhere with the plumber I will do a sketch of the overall
> system, as you suggested.
>
> Thinking about it, surely the pump is currently in the 'return leg',
> but facing the wrong way?
>
Why? If it's in the return leg, it *has* to face the boiler - otherwise it
*ain't* the return leg!
Harry Bloomfield
> That would be hard as the pipe to the tank is full even when cold. To do
> what you propose would require a magic ballcock that cut off when the water
> was several feet down the pipe below the base of the tank!
No magic involved...
The boiler, rads, pipe and tank will of course all be full of cold
water initially. As the system heats up there will be point at which
the water in the pipe will hot below a certain level and cold above it.
As the water warms and expands, the interface between the two will
gradually rise up that pipe.
Thermo mixing will be a minimum in a narrow pipe, unless and until the
hot water expands up to the tank, where it should quickly mix with the
cold water in there and the tank will then cool. A warm header tank
means something is wrong.
Tim W
wibbled on Sunday 06 December 2009 22:01
OK - I see what you are saying - my bad. I though you were saying there
would be no appreciable increase in the water level in the tank. You were
actually saying the tank shouldn't get hot.
My apologies...
David J
Dave, many thanks for this very comprehensive reply, which I have
printed out. My thoughts now are that your Item 2 covers this problem.
#Whether the pump is in backwards we will establish later with the
plumber. Now, after reading all the replies when folks realised the it
was a gravity/pumped system, I'm not so sure again.
What I can do this morning is to restart the system, with the pump on
the lowest speed setting, and see how it all performs. I can check
what is going on in the header tank as well.
David
John Rumm
> Thermo mixing will be a minimum in a narrow pipe, unless and until the
> hot water expands up to the tank, where it should quickly mix with the
> cold water in there and the tank will then cool. A warm header tank
> means something is wrong.
That does not really stand up to scrutiny. Much will depend on the
layout of the pipework, and how much head the tank has got. In many
cases where the tank is only a couple of feet above the normal flow
pipes, a couple of litres of expansion can easily be enough to drive
some hot water to the header by expansion alone. The starting and
stopping of the pump etc will also help mix the water as it causes
surges in the level.
So while a header tank steaming away full of 80 degree water is a good
indication of substantial pumping over, one that is "warm" may be quite
normal for a given installation.
Roger Mills
David J <da...@btelecom.invalid> wrote:
>
> Dave, many thanks for this very comprehensive reply, which I have
> printed out. My thoughts now are that your Item 2 covers this problem.
>
> #Whether the pump is in backwards we will establish later with the
> plumber. Now, after reading all the replies when folks realised the it
> was a gravity/pumped system, I'm not so sure again.
>
> What I can do this morning is to restart the system, with the pump on
> the lowest speed setting, and see how it all performs. I can check
> what is going on in the header tank as well.
>
> David
May I suggest that when you first turn the system on, you set it to HW-only
mode and note whether or not the pump starts. If it's a fully pumped system,
the pump *will* start on HW-only. If it's gravity HW and pumped CH, the pump
won't run until you also turn the CH on. That should help to determine what
sort of system it is.
Harry Bloomfield
> My apologies...
No problem!
David J
You are quite right there , of course. I checked the C/H piping
layout against your sketch here:
http://www.mills37.plus.com/Heating.pdf and it is identical.
I can put a line under this story now, I hope. The original plumber
came this afternoon as promised, and heard the tale from me.
He confirmed that he has installed the new pump correctly, but
conceded that his leaving the pump on the max speed (70) was an error
and could have caused the overpumping which he could see had been
happening recently. So he apologised for that, and agreed that the
pump should be left on the minimum speed (36) for now. If cold weather
later shows that the rads cannot cope, the pump speed can go to the
middle (58) range. There are only 6 rads in the s/det. house.
We then noticed that one rad upstairs that was OK with the max speed,
was now only luke-warm and possibly sludged. He said that this could
also have contributed to the earlier overpumping.
This C/H system has had no attention for at least a decade, so it was
agreed that he would return in the Spring to possibly replace one rad
that has been weeping from a rusting bleed thread, flush the entire
system and add some corrosion inhibitors. This was a no-charge visit,
but he has the promise of another job next year.
David
Dave Baker
"David J" <da...@btelecom.invalid> wrote in message
> I can put a line under this story now, I hope. The original plumber
> came this afternoon as promised, and heard the tale from me.
>
> He confirmed that he has installed the new pump correctly, but
> conceded that his leaving the pump on the max speed (70) was an error
> and could have caused the overpumping which he could see had been
> happening recently. So he apologised for that, and agreed that the
> pump should be left on the minimum speed (36) for now. If cold weather
> later shows that the rads cannot cope, the pump speed can go to the
> middle (58) range. There are only 6 rads in the s/det. house.
>
> We then noticed that one rad upstairs that was OK with the max speed,
> was now only luke-warm and possibly sludged. He said that this could
> also have contributed to the earlier overpumping.
The blocked rad can't have been affecting anything provided it, and all the
others of course, are on the pressure side of the pump and the vent is on
the return. If blocked rads caused overpumping then it would happen every
time a TRV shut the flow off. Remember also that rads in a circuit are
fitted in parallel not in series otherwise if one rad's TRV shut down it
would block the flow to all the rest. There's always a bypass pipe.
Doesn't sound like he's the sharpest tool in the box to be honest.
--
Dave Baker
Dave Baker
"Dave Baker" <Nu...@null.com> wrote in message
news:hfl4tk$3au$1...@news.datemas.de...
I should just add that a pump circuit should always be arranged thus.
Pump --> Boiler --> Rads/Immersion --> Vent --> Pump.
That minimises the temperature of the water the pump has to deal with which
is good for pump life. If there's anything with a resistance to flow between
the vent and the pump then it will contribute to overpumping so the vent
should be as close to the pump as possible and upstream of it.
--
Dave Baker
David J
Many thanks for all the advice given here. I've had C/H myself since
the 1960's - I even put one in an early house with the help of a mate,
before it was common-place. He was handy with a blowtorch and showed
me how to deal with York Fittings! But I have never before experienced
the phenomena of 'Pumping over', and it was quite a shock to see this
in another person's house last week.
That house has quite a mixed bag of different aged radiators. The one
in the downstairs lounge is actually on the upstairs circuit. Solid
floors have prevented a tidy pipe run for that one, I suppose.
Ref your: "Doesn't sound like he's the sharpest tool in the box to be
honest". Have you ever heard of the expression NFN? Normal for
Norfolk, which is where we are!
Ref your: Pump --> Boiler --> Rads/Immersion --> Vent --> Pump.
The circuit in this house is similar to that given by Roger for a
gravity/pumped system, ie, the c/h vent is a 1/2" continuation of the
gravity 1" return pipe from the cylinder. The gravity h/w and the rad
water are mixed inside the boiler, so are all the same water, wrt
expansion are they not?
Finally he mentioned putting 2 inhibitors into the system after it is
drained down next year for a flush. I just had Fernox anti-corrosion
put into my own system last year. What else could he be referring to
there?
David
>