COMBI BOILER, PRESSURE TOO HIGH

rotherman · 25 Nov 2008

I have a Baxi 105e instant, noticed when the heating was on the pressure reached 3.0 Bar, then the relief valve opened and it dropped to 2.5Bar, it was suggested I repressurise the expansion vessel.
So I set it to 1Bar and the operating pressure remained rock solid, and I observed it over the next seven days, although the operating pressure remained steady each day it had increased until by the end of the week it had reached 3Bar,over the same period the cold pressure decreased and I had to top up with water.
I suspect the expansion vessel may need replacing, any idea how much this would cost or can anyone suggest another resolution.

Regards Rotherman

GPlumb · 25 Nov 2008

If the vessel isn't leaking water then you could try replacing the valve on it. Cost about £1.

MANDATE · 25 Nov 2008

I had a similar problem recently so can only ask if did what I did.
Did you test the expansion vessel by depressing the valve and if so did any water come out, indicating a hole in the diaphram.
Also did you apply the correct procedure by draining off water before recharging the air pressure on the expansion vessel.
I understand the Pressure Relief Valves don't always seal properly once opened, so that could be a reason for the cold pressure to reduce.
I fastened a clear plastic bag to the pressure relief outlet pipe and there is clear evidence that a small amount of water is escaping and it does mean I have to increase the pressure once in a while.

kitch0978 · 25 Nov 2008

if you do need to have a new expansion vessel then just get an external one and have it installed onto one of your heating pipes somewhere in the system.....any pipe flow or return...hide it under the floor or you can mount it up on the wall next to your boiler......get PRV changed st the same time.......

rotherman · 25 Nov 2008

Hi Mandate ,
I pressed the valve on the expansion vessel and AIR came out, so I closed off the the valve on the central heating return pipe, and drained the boiler(situated in the loft), 3 to 4 letres I guess, when I was sure all the water was out I pressurised the vessel to 1 Bar. which remained steady so I replaced the dust cap and opened the valves to refil the system and set to 1 bar. With the central heating on the operting pressure was steady at about 1 bar, thought I had cracked it

Regards Rotherman

MANDATE said:
I had a similar problem recently so can only ask if did what I did.
Did you test the expansion vessel by depressing the valve and if so did any water come out, indicating a hole in the diaphram.
Also did you apply the correct procedure by draining off water before recharging the air pressure on the expansion vessel.
I understand the Pressure Relief Valves don't always seal properly once opened, so that could be a reason for the cold pressure to reduce.
I fastened a clear plastic bag to the pressure relief outlet pipe and there is clear evidence that a small amount of water is escaping and it does mean I have to increase the pressure once in a while.

MANDATE · 25 Nov 2008

what you did seems ok. Time to try the plastic bag idea, maybe the PRV is not fully sealing. I note kitch0978 advises new PRV, that must tell you something

clarkerothwell · 25 Nov 2008

Another problam is a blockage on the pipe from the expansion vessel, there for cutting the vessel out of the system altogether (usually a flexy silver pipe simlar to a filling loop tube, although can be copper too), if this is blocked with debri then water can only expand back into the system.

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COMBI BOILER, PRESSURE TOO HIGH

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