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Central Heating

Pressure increase in central heating

I have a combi boiler and recently I have noticed that the pressure in the CH circuit seems to increase without me adding water, it has grown over a number of days to a point where I need to bleed water from the radiators to keep it in the recommended range. Initially I thought it may be a leak from the water top up loop so I replaced tap but I now know it is not that as I have infact disconnected the loop to prove it is not.

It may be when we run the hot water that it happens although I have yet to test my theory, I have checked my radiators and they have no air in them I can detect so the water I am taking out of the system is being replaced somehow. The boiler is a Baxi although not sure on the model, although does not look new.

Anyone any ideas what is wrong here?

Update: Bottom line - Plate exchanger had rusted through allowing water from DHW side to leak into CH side over time pressurising the system allowing me to continually remove water without depressurising the system. Fixed by replacing the plate exchanger.

3 Answers from MyBuilder Heating Engineers

Best Answer

You need a Gas Man to come and pump up your Expansion Vessel with 1 bar of air (with a Foot Pum0)
make sure he knows what he is doing!
Expansion Vessel It will NOT be Split.
It just needs pumping up with Air
Change the PRV Valve as well.
If the Gas Man Does not have a Foot Pump you have hired the Wrong Guy.
This will fix it.
Don't listen to any Rubbish about Changing the Boiler Because the Expansion Vessel is Split it just needs Pumping up with Air


Answered 21st Jan 2015

Agree with full flame, expansion vessel recharge, you don't need to release pressure manually as boiler will do this itself via pressure relief valve (blow off)
As full flame said engineer should have correct pump plus there is a correct method to recharge vessel it involves isolating the boilers inlet pipes via taps at boiler and at the time of pressurising vessel hold PRV open


Answered 25th Jan 2015

Take no notice of the above post saying to hold PRV open. You can do this if you want to replace the PRV. If not don't do it. It causes the PRV to pass water and will need replacing.

A Baxi trained engineer.


Answered 24th Feb 2015

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