Megaflow problem
Janet Bale
New pressure/temp valve fitted. New combination valve assembly fitted.
Over pressure valve on water inlet still bleeds. Regulator factory set
to 3 bar. Over pressure valve factory set to trigger at 8. What possible
problems or faults match these symptoms?
John
"Janet Bale" <netp...@texas.net> wrote in message
news:dth3ej$jen$1...@nwrdmz03.dmz.ncs.ea.ibs-infra.bt.com...
Failed air bubble - read the replenishment instructions
Aidan
> Model CL250. Over pressure valve on cold water inlet bleeds warm water.
i.e., expansion relief valve dripping; refill air bubble as stated
above. The expansion bubble/expansion tank isn't required in most other
countries, where the expansion relief valve just dumps the extra water
volume down the drain. The expansion tank or bubble is a UK Water
Bylaws requirement to prevent waste of water.
> New pressure/temp valve fitted.
Why? They would have had to drain the heater, and so refill the air
bubble, to fit a new T&P relief valve. The T&P valves rarely fail.
> New combination valve assembly fitted.
Why?
> Over pressure valve on water inlet still bleeds.
I've been told that you can get a recurring loss of the air bubble in
some areas, due to the water quality. In this case the fix is to fit an
external expansion tank, or refill the air bubble regularly. Ring the
manufacturers for technical advice.
Anyone doing work on an unvented water heater should have passed the
relevant training course (IoP, CITB, etc., ). If you're going to ask
for a refund for any unnecessary work from the installer, ask for the
relevant certificate number and check with the issuing body.
Aidan
If all else fails, you could always resort to reading the manual which
should have come with the heater or, if not, it is available on the
Heatrae Sadia website.
The manual says;
Water discharges from Expansion Relief Valve
1. INTERMITTENTLY
Expansion volume has reduced within unit. See Section 7.4 for
recharging procedure
2. CONTINUALLY
a. Cold Water Combination Valve Pressure Reducer not working
correctly.
Check pressure from Cold Water Combination Valve. If greater than 3 bar
replace Pressure Reducer cartridge
b. Expansion Valve seat damaged. Remove Expansion Valve
cartridge.
Check condition of seat. If necessary fit new Expansion Valve
cartridge.
I couldn't have put it better myself.;-)
Janet Bale
suggestions have been tried. Heatrae technical help have offered an
explanation for the bubble loss and suggested a fix. If they are correct
I can also see another way to remove the problem. If either are
successful I will report in full for the benefit other others.
Thanks,
Martin
Aidan
Janet Bale wrote:
> Heatrae technical help have offered an
> explanation for the bubble loss and suggested a fix.
Could you tell us what that is, please?
Thanks
Janet Bale
Martin
Aidan
Janet Bale wrote:
> >Could you tell us what that is, please?
> >Thanks
>. There are three shower mixers and other mixer taps.
> Heatrae suggested that one or more mixers were bleeding cold water
> across to the hot water system thus raising the pressure in the Megaflo
> to the point where the inlet valve blows at 8 bar and a reverse flow
> occurs with hot water pouring down the tundish. Their solution was to
> fit a double check valve on the hot water outlet of the Megflo.
Thanks; I've not heard of that happening.
It's a common installation problem where the Megaflo is some distance
from where the CWM enters the building.
Another option might be to fit a strainer & a pressure reducing valve
on the cold water mains supply, to reduce the cold pressure to the 3.5
(?) bar the Megaflo operates at. Presumably the CWM is more accessible,
since you've been able to put a pressure gauge on it. The disadvantage
is that you've got 2 sets of pressure reducing valves where one might
have done & the Megaflo pressure reducing valve is only getting a 3.5
bar supply, unless you can put in a dedicated supply pipe..
Aidan
Aidan wrote:
Same problem discussed (& resolved) here;
http://www.screwfix.com/talk/thread.jspa?threadID=24253&messageID=237453#237453
NB the mention of the occasional loss of pressure.
The manufacturer's explanation doesn't quite make sense; if that was
happening, you'd get a cold shower & the expansion relief valve (6 bar
?) would operate before the T&P relief valve (8 bar?). You should
notice the water being discharged.
> bar supply, unless you can put in a dedicated supply pipe.
Ignore that; if you could do that, then you'd be able to connect the
cold supply to the tee after the Megaflo multi-function valve.
Doctor Drivel
The Megaflo feeds the hot water system in a holiday rental barn conversion.
The cold water is all at mains pressure, hence the system is not balanced.
There are three shower mixers and other mixer taps. Heatrae suggested that
one or more mixers were bleeding cold water across to the hot water system
thus raising the pressure in the Megaflo to the point where the inlet valve
blows at 8 bar and a reverse flow occurs with hot water pouring down the
tundish. Their solution was to fit a double check valve on the hot water
outlet of the Megflo. This cured the problem completely. I also fitted a
pressure gauge on the cold inlet so that this can be monitored. Obviously a
proper solution would be to connect the cold system to the cold tee off on
the regulator. This would stop the hot water system being raised in
pressure. However the tight space and complexity of pipe work makes this at
least half a days work plus materials. Now that all is apparently well, the
customer is taking some convincing that they should go for this.
<<<<
Martin
I don't like unvented cylinders for many reasons. The one you gave is more
common than what you think. They also require an annual service just to
store water, and this alone precludes them for me. They also "typically" do
not operate at high pressures as a heat bank can. Large bore pressure relief
pipes are needed too. And the relief pipe can drip more often than you may
want (a London borough replaced all its unvented cylinders because of the
constant dripping on the pavements below. They also have a far higher risk
of explosion than vented systems. http://www.waterheaterblast.com
A thermal store or heat bank is about the same price and much superior all
around, and can supply the CH using TRVs all around, and eliminate boiler
cycling.
Janet Bale
Aidan wrote:
Aidan wrote: Same problem discussed (& resolved) here; http://www.screwfix.com/talk/thread.jspa?threadID=24253&messageID=237453#237453 NB the mention of the occasional loss of pressure. The manufacturer's explanation doesn't quite make sense; if that was happening, you'd get a cold shower & the expansion relief valve (6 bar ?) would operate before the T&P relief valve (8 bar?). You should notice the water being discharged.
I don't know if the CL210 is different to the CL250 but the expansion relief valve is 8 bar whilst the T/P valve is 90C/10 bar. This is why the T/P valve does not go first. I can now say to the customer that if her shower mixers are not rated that high then she should have the cold side corrected. Or maybe even if the mixers were rated at over 10 bar for a balanced supply, they would not stand that amount of imbalance?
bar supply, unless you can put in a dedicated supply pipe.Ignore that; if you could do that, then you'd be able to connect the cold supply to the tee after the Megaflo multi-function valve.
Doctor Drivel
Aidan wrote:
Aidan wrote:
cold supply to the tee after the Megaflow multi-function valve.
Yes, tight space with several cold tee offs close together make this
difficult.
Doesn't the Megaflow have a pressure equalising valve on the cold inlet to
the Megaflow? All cold is supposed to be taken from this valve at the
cylinder. It equalises the hot and cold but does not take into account
pressure loss through the megaflow, which appears to be the problem here, so
an imbalance of hot and cold pressure at the appliances. Mixers with
pressure equalisation valves can do the trick, or a 22mm pressure
equalisation valve on the megaflow outlet and all appliances have their cold
taken from this, then the pressure drop across the Megaflow is taken into
account.
Doctor Drivel
Aidan wrote:
Janet Bale wrote:
Heatrae technical help have offered an
explanation for the bubble loss and suggested a fix.
Could you tell us what that is, please?
Thanks
The Megaflo feeds the hot water system in a holiday rental barn conversion.
The cold water is all at mains pressure, hence the system is not balanced.
There are three shower mixers and other mixer taps. Heatrae suggested that
one or more mixers were bleeding cold water across to the hot water system
thus raising the pressure in the Megaflo to the point where the inlet valve
blows at 8 bar and a reverse flow occurs with hot water pouring down the
tundish.
<<<<
Was this discharge continuous when the mixers were in use?