Gas pressure and boiler problem
Pete Zahut
faultlessly for the last 3 and a half years (in fact, it's been bloody
brilliant :o)) but, about 2 months ago, it started playing up and locking
out intermittently. Sometimes it'll reset first time, sometimes not. When it
does reset, you can hear a slight "whumph" as the gas ignites.
We have the Alpha Aftercare contract so for just �12/month all parts and
labour are covered, so it's just a matter of a phone call and someone comes
out (usually) the same day to sort it. Over the last two months they've
changed the spark generator, the gas valve and the gas valve lead (which
apparently is a resistive lead and can be damaged if the spark genny fails -
or so they said anyway).
They've just been out again today and the Alpha (or I should more correctly
say the Alpha sub-contracted agency) guy measured a standing gas pressure of
23mbar at the boiler but when the boiler was trying to light he said that it
dropped down to 15 or 16mbar, which was too low. He said that I should
contact British Gas to report low pressure and they would sort it
(incidentally, the whole estate got new gas meter, governor and main out to
the street 12 months ago).
Anyway, National Grid/BG guy turned up within 20 minutes and measured
working pressure (all 4 rings on the cooker lit and boiler providing hot
water) at the meter as 21mbar (their range being 19 - 23mbar) so that's OK.
Assuming we haven't got a gas leak (no smells at all) they reckon it could
be crud in the pipework. My question (at last, I hear you cry) is this: (a)
how does crud get into a gas pipe in the first place and (b) how the hell do
you get it out? Is it likely, or is it that they don't know what to do next
so are blaming anything?
Pete
Pete Zahut
> We have an Alpha CD32C condensing boiler up in the loft that has
> worked faultlessly for the last 3 and a half years (in fact, it's
> been bloody brilliant :o)) but, about 2 months ago, it started
> playing up and locking out intermittently. Sometimes it'll reset
> first time, sometimes not. When it does reset, you can hear a slight
> "whumph" as the gas ignites.
> We have the Alpha Aftercare contract so for just �12/month all parts
> and labour are covered, so it's just a matter of a phone call and
> someone comes out (usually) the same day to sort it. Over the last
> two months they've changed the spark generator, the gas valve and the
> gas valve lead (which apparently is a resistive lead and can be
> damaged if the spark genny fails - or so they said anyway).
>
> They've just been out again today and the Alpha (or I should more
> correctly say the Alpha sub-contracted agency) guy measured a
> standing gas pressure of 23mbar at the boiler but when the boiler was
> trying to light he said that it dropped down to 15 or 16mbar, which
> was too low. He said that I should contact British Gas to report low
> pressure and they would sort it (incidentally, the whole estate got
> new gas meter, governor and main out to the street 12 months ago).
>
> Anyway, National Grid/BG guy turned up within 20 minutes and measured
> working pressure (all 4 rings on the cooker lit and boiler providing
> hot water) at the meter as 21mbar (their range being 19 - 23mbar) so
> that's OK.
Doh, sorry - that should read 3 rings lit on the cooker, boiler providing
hot water and 19mbar at the meter. Standing pressure with nothing on was
21mbar.
Andrew Gabriel
Could be that the pipe is too small a bore for its length.
There are tables for working out pressure drop given length,
bore, and numbers of bends. However, the fact that it has worked
for 3+ years, presumably with the same pipe run, would cast doubt
on that being the issue.
Your Alpha sub-contractor should have measured the pressure at the
meter outlet when the boiler was firing up before suggesting calling
out Transco. To be honest, it sounds like the subcontractor doesn't
know what he's doing, given the number of failed repair attempts.
I suggest you go back to Alpha Aftercare and ask for a different
person.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
Pete Zahut
No, I can't see it being a pipe-sizing issue either because it really has
been marvellous for more than 3 years.
> Your Alpha sub-contractor should have measured the pressure at the
> meter outlet when the boiler was firing up before suggesting calling
> out Transco. To be honest, it sounds like the subcontractor doesn't
> know what he's doing, given the number of failed repair attempts.
> I suggest you go back to Alpha Aftercare and ask for a different
> person.
Hmm... tend to agree with you there Andrew. Cheers mate.
Pete
Toby
Unless, I suppose, the new gas meter (and presumably regulator) was
outputting a higher pressure before, it was then replaced with a new
one, that was also on the high side, and this has now reduced slightly
to become just out of tolerance for the boiler?
Toby...
John Rumm
> They've just been out again today and the Alpha (or I should more correctly
> say the Alpha sub-contracted agency) guy measured a standing gas pressure of
> 23mbar at the boiler but when the boiler was trying to light he said that it
> dropped down to 15 or 16mbar, which was too low. He said that I should
> contact British Gas to report low pressure and they would sort it
> (incidentally, the whole estate got new gas meter, governor and main out to
> the street 12 months ago).
>
> Anyway, National Grid/BG guy turned up within 20 minutes and measured
> working pressure (all 4 rings on the cooker lit and boiler providing hot
> water) at the meter as 21mbar (their range being 19 - 23mbar) so that's OK.
That sounds a bit suspect. The static pressure tells you nothing in
particular in this case - however the pipe sizing should be such that
there is not that much fall in pressure on load. The transco bod seems
to have confirmed that the meter and governor are doing their stuff
(although normally they arrange it such that the system will provide
21mBar on load at the meter. That allows for a 1mBar drop in your
pipework, and the dynamic pressure at the boiler test point to be near
enough 20mBar).
> Assuming we haven't got a gas leak (no smells at all) they reckon it could
You would need a substantial leak to drop that much pressure!
> be crud in the pipework. My question (at last, I hear you cry) is this: (a)
> how does crud get into a gas pipe in the first place and (b) how the hell do
> you get it out? Is it likely, or is it that they don't know what to do next
> so are blaming anything?
Probably the latter.
It could be the supply pipe is a tad undersized and some other change in
the supply pressure has made this significant.
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
cynic
If work was done on the gas mains there is every chance that "some"
debris may have been dislodged and ended up in your system. I have
come across clogged inlet filters on domestic gas valves. I cannot say
if your boiler model has a gas valve incorporating an inlet filter but
Ed may be able to help here. I have also come across jobs where the
gas main pressure varies depending on the time of day (all the other
houses in the street cooking tea with boilers running etc) so Transco
toddle along at some other time and find no fault.
You really need an engineer with time to dig into the problem and sort
it out fully. I suspect the answer will lie downstream of the meter
YAPH
> They've just been out again today and the Alpha (or I should more
> correctly say the Alpha sub-contracted agency) guy measured a standing
> gas pressure of 23mbar at the boiler but when the boiler was trying to
> light he said that it dropped down to 15 or 16mbar, which was too low.
> He said that I should contact British Gas to report low pressure and
> they would sort it (incidentally, the whole estate got new gas meter,
> governor and main out to the street 12 months ago).
>
> Anyway, National Grid/BG guy turned up within 20 minutes and measured
> working pressure (all 4 rings on the cooker lit and boiler providing hot
> water) at the meter as 21mbar (their range being 19 - 23mbar) so that's
> OK.
>
> Assuming we haven't got a gas leak (no smells at all) they reckon it
> could be crud in the pipework. My question (at last, I hear you cry) is
> this: (a) how does crud get into a gas pipe in the first place and (b)
> how the hell do you get it out? Is it likely, or is it that they don't
> know what to do next so are blaming anything?
So you've got 21mbar at the meter under load (including the boiler
providing hot water, which is likely to be its maximum load) but only 15
or 16mbar at the boiler itself. How much, if any, 15mm pipework is there
in the supply line, and how much of that is elbows (sharp right angle
bends)? And what is the length of 22mm pipework, in metres? How many
elbows or tees where the gas flow makes a sharp 90 degree bend?
And what's the rating of the boiler?
As a rule of thumb for a 24kW boiler I reckon about 22 metres of 22mm
pipework, where you count 0.5m for each 90 degree bend, is the limit. Even
1 metre of 15mm pipework (with the sae allowance for elbows) is too much.
--
John Stumbles -- http://yaph.co.uk
The astronomer married a star
John Rumm
> As a rule of thumb for a 24kW boiler I reckon about 22 metres of 22mm
> pipework, where you count 0.5m for each 90 degree bend, is the limit. Even
> 1 metre of 15mm pipework (with the sae allowance for elbows) is too much.
It was a 32kW boiler was it not? So about 15m effective length of 22mm
tops.
YAPH
> It was a 32kW boiler was it not? So about 15m effective length of 22mm
> tops.
Ah! "Alpha CD32C" - yes looks like it.
--
John Stumbles -- http://yaph.co.uk
Testiculate [v.t]
To wave one's arms around while talking bollocks.
Pete Zahut
> On Tue, 09 Jun 2009 00:31:08 +0100, John Rumm wrote:
>
>> It was a 32kW boiler was it not? So about 15m effective length of
>> 22mm tops.
>
> Ah! "Alpha CD32C" - yes looks like it.
Just been trying to guesstimate the pipe run - didn't do the job myself for
various reasons. Anyway, I _think_ that there's about 22m (including elbows
and 90deg bends) of 22mm pipe - no 15mm in the run at all. I'm grateful for
all help given by you folks but I really don't see how the pipe run/pipe
size could be the problem because it's been working brilliantly for 3+
years - although, obviously, you're the experts and I'm willing to learn
:o)
Pete
John Rumm
It sounds like it has always been wrong - but something else was hiding
the fault.
The difficulty you now have is that the pressure at the meter looks ok
(perhaps a little low - but not far out), but the pipe is demonstrably
undersized. So you may find the only way back to a working system (or at
least one where it can't be used as an excuse for another fault) is to
upgrade the pipe.
YAPH
> Just been trying to guesstimate the pipe run - didn't do the job myself
> for various reasons. Anyway, I _think_ that there's about 22m (including
> elbows and 90deg bends) of 22mm pipe - no 15mm in the run at all. I'm
> grateful for all help given by you folks but I really don't see how the
> pipe run/pipe size could be the problem because it's been working
> brilliantly for 3+ years
But you said:
> ... about 2 months ago, it started playing up...
...
> (incidentally, the whole estate got new gas meter, governor and main out
> to the street 12 months ago).
So it's been playing up *since* your new meter was installed. Some
connection maybe?
If you can replace about 6 metres-worth (preferably a bit more) of 22mm
with 28mm you should be OK. It doesn't have to be the run right from the
meter: any convenient length(s) that you can get at will do.
(28mm has as near as dammit zero resistance at the flow rates we're talking
about: it's something like a power-of-4 relationship so a few inches of
15mm, a few tens of metres of 22mm or probably some hundreds or so metres
of 28mm have the same flow resistance. For exact figures I think the CDA
website has some tables or graphs.)
--
John Stumbles -- http://yaph.co.uk
My karma ran over my dogma
Doctor Drivel
"Pete Zahut" <dont@bother> wrote in message
news:zsadnXg6ivbbs7PX...@bt.com...
Size it up from here:
http://www.copperinfo.co.uk/webcasts/domestic-gas-pipework-pipe-sizing/player.html
If OK, which on the surface it appears not to be as 22m of 22mm pipe is over
60 foot, but check, then you need a shock pump. The gas pipe is
disconnected at the boiler and meter. The pump is charged by hand, and the
pressure let loose in one blast. It usually shifts any blockage, or may
move it if you are unlucky.
If installing 28mm install it from the meter only, with a 28mm meter union.
available from http://www.bes.co.uk
Gas pressure has to be tested at the meter and the boiler. If OK at the
meter when the boiler is on, then is it OK at the boiler. Before the new
district governor was fitted, the gas rate pressure may have been too high,
hiding the undersized pipe problem.
Doctor Drivel
"Doctor Drivel" <kill...@invalid.invalid> wrote in message
news:h0nr07$5cb$1...@news.eternal-september.org...
If you install a length of 28mm pipe at the meter, it is best to ensure the
cooker pipe is a dedicated supply back to the meter teeing into the 28mm.
Then one does not rob the other.
baz
ia ma experienceing same problem with a worcester bosch boiler.worked ok for
severl years,played up last year so pcb and a couple of other parts replaced
such as gas valve.
despite last years probllems boiler has always deliverd good hw and ch but
since christmas hw and ch temps have dropped dramatically.
service engineer came 2 weeks ago out reckoned tested and said i didnt have
enough gas pressure at the boiler. ansd need to put in bigger pipe size<its
22mm right now.transco reckon i have 22mb at meter which is more than
sufficicent.
service company reckon gas pipe from meter to boiler to small,so how come
its worked fine for 7 years i ask them no answer. got any clues its driving
us round the bend.i cant see why suddenly out of the blue the gas pipe is to
small to deliver the right colume of gas.
Jim
> just seen your posting
> ia ma experienceing same problem with a worcester bosch boiler.worked ok for
> severl years,played up last year so pcb and a couple of other parts replaced
> such as gas valve.
> despite last years probllems boiler has always deliverd good hw and ch but
> since christmas hw and ch temps have dropped dramatically.
Is it a combi?
> service engineer came 2 weeks ago out reckoned tested and said i didnt have
> enough gas pressure at the boiler. ansd need to put in bigger pipe size<its
> 22mm right now.transco reckon i have 22mb at meter which is more than
> sufficicent.
> service company reckon gas pipe from meter to boiler to small,so how come
> its worked fine for 7 years i ask them no answer. got any clues its driving
> us round the bend.i cant see why suddenly out of the blue the gas pipe is to
> small to deliver the right colume of gas.
Depending on the distance and the number of bends 22mm may not be enough.
Have a look at this PDF from Worcester Bosch which explains a
rule-of-thumb method for calculating what size of pipe you need. The
boiler requirement in metres cubed/hour should be somewhere in your
boiler manual.
http://www.worcester-bosch.co.uk/cache/file/27/undersized-gas-supply-pipework.pdf
Doctor Drivel
"baz" <j...@tnt.com> wrote in message
news:d35a2a82d34f4890...@newspe.com...
When the boiler is full on, the gas fire full on and three rings on the hob,
there is to be no more than 1 mb drop in pressure from the meter to the
boiler. 22mb at meter, 21mb at boiler.
Usenet Nutter
Dunno where this post originated as my newsreader only shows the
follow up from Jim to Baz .
Is it likely that at no time in 7 years the boiler,gas fire and 3
rings have been on together as he says it has worked fine in that time
.
Graham.
>
> Dunno where this post originated as my newsreader only shows the
> follow up from Jim to Baz .
Because the OP replied to a thread started in June last year via a dodgy
leeching web service.
Here is the entire thread courtesy of another dodgy leeching webservice ;-)
http://groups.google.co.uk/group/uk.d-i-y/browse_thread/thread/8774cb2b0c1d6586/
--
Graham.
%Profound_observation%
YAPH
> When the boiler is full on, the gas fire full on and three rings on the
> hob, there is to be no more than 1 mb drop in pressure from the meter to
> the boiler. 22mb at meter, 21mb at boiler.
Or as we qualified, registered professional installers say: "21mb at the
meter, 20mb at the appliance"
<sigh!>
--
John Stumbles -- http://yaph.co.uk
I used to be indecisive but now I'm not so sure
Onetap
> Or as we qualified, registered professional installers say: "21mb at the
> meter, 20mb at the appliance"
Nominal 21 +/1 mb at the meter outlet; 19 to 23 mb, depending on flow
rate.
I'd suspect the gas pressure is a red herring. It may be the cause of
the fault; possibly the supply pressure drops at times of peak
demand.
The explosive ignition can be caused by water in the combustion
chamber, either a leak or condensation from the flue running back. I
wouldn't think it likely that it is caused by a slightly low gas
pressure. Did the fault coincide with the cold weather?
Onetap
Also spark generator wiring had been changed and makes a difference,
allaegedly.
Doctor Drivel
"Onetap" <One...@talk21.com> wrote in message
news:f6adc3d1-bfa7-4d01...@j19g2000yqk.googlegroups.com...
> On 15 Jan, 20:23, YAPH <use...@yaph.co.uk> wrote:
>
>
>> Or as we qualified, registered professional installers say: "21mb at the
>> meter, 20mb at the appliance"
>
> Nominal 21 +/1 mb at the meter outlet; 19 to 23 mb, depending on flow
> rate.
Yep.
> I'd suspect the gas pressure is a red herring. It may be the cause of
> the fault; possibly the supply pressure drops at times of peak
> demand.
> The explosive ignition can be caused by water in the combustion
> chamber, either a leak or condensation from the flue running back. I
> wouldn't think it likely that it is caused by a slightly low gas
> pressure. Did the fault coincide with the cold weather?
What type of burners is it? pre-mix? If so, theses are susceptible to poor
pressure and fluctuations.
Doctor Drivel
"Usenet Nutter" <indivi...@takeoutmyteethgmail.com> wrote in message
news:g811l5lfr323vo6p9...@4ax.com...
That is the regs. It is probably the case that all have never been on, but
the test is with all on.
Richard Russell
> service company reckon gas pipe from meter to boiler to small,so how come
> its worked fine for 7 years i ask them no answer. got any clues its driving
> us round the bend.i cant see why suddenly out of the blue the gas pipe is to
> small to deliver the right colume of gas.
With respect, this is wooly thinking. A system will always be
designed with a safety margin so if, for example, it's specified to
run down to 18mb it will probably run happily at 16mb *when every part
of the system is new*. As the system ages, and various components
deteriorate, this safety margin will be eaten into. Eventually it may
only work properly at the specified 18mb.
You can't then turn around and say "but it worked before, so it can't
be the pressure". Just because the boiler used to work at a lower
pressure than it was specified to, it doesn't mean you can expect that
always to be the case.
Richard.
http://www.rtrussell.co.uk/
tony sayer
s.com>, Richard Russell <ne...@rtrussell.co.uk> scribeth thus
So what might -vary- in that would require more pressure?..
>
>Richard.
>http://www.rtrussell.co.uk/
--
Tony Sayer
Doctor Drivel
"tony sayer" <to...@bancom.co.uk> wrote in message
news:OwYwC5LO...@bancom.co.uk...
Burners wear - the holes can get larger in time, affecting performance and
efficiency.. A burner's fan can increase or reduce speed affecting
performance as well.