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i recently replaced the pressure relief valve on my halstead ace high boiler because the pressure kept dropping everyday, now when the central heating comes on the pressure drops and have to keep topping up. When using only hot water pressure is ok.
pressure is ok when only using hot water but as soon as CH is on presure will drop, what could be the problem, plz advise in detail.
could there be a leak in the CH and how to fix? how to check for leak in CH?
Other fault why bolier is losing pressure when heating is on. please advise. thanks

Does pressure rise when CH in use ?

Check all pipework, radiators, radiator valves and boiler for leaks.


htg

yes pressure does rise when CH is on and once when CH is switched off pressure will drop.
i just went round checking all rads and found a rad upstairs with the tiniest leak. i dryed the area and went back to check it a litlle later and found it to be a little wet. the surrounding area is all dry around the carpet, is this enough to make the pressure drop, is it just a matter of tightening up the fixings on the rad.
also i put a bag over the pressure relief valve outlet pipe and found that it had filled up with water when the CH is on,please advise further.

thanks in return htg

Hi

Close off all the valves under the boiler for the flow and return. If the pressure continues to drop then the leak is in the boiler, if it doesn't then the leak is on the system somewhere, and that means searching all the pipework with a fine toothcomb!

following on from HTG, when the CH comes on does the pressure rise rapidly?

AH

[quote="irshy"]i recently replaced the pressure relief valve on my halstead ace high boiler because the pressure kept dropping everyday, now when the central heating comes on the pressure drops and have to keep topping up. When using only hot water pressure is ok.
pressure is ok when only using hot water but as soon as CH is on presure will drop, what could be the problem, plz advise in detail.
could there be a leak in the CH and how to fix? how to check for leak in CH?
Other fault why bolier is losing pressure when heating is on. please advise. thanks[/quote]
sounds like the expansion vessel has lost its charge or has ruptured. this can be tested by isolating the boiler flow and return then opening the pressure relief valve then using a tyre pressure gauge on the vessel [ normally located on top at rear of boiler]if no pressure present try inflaing to 1.5 bar using a foot/bike pump if it fails to hold pressre then vessel is ruptured internally. normally cheaper to fit an equivelant size vessel on the flow pipe. if pressure holds then its possibly a leaking heat exchanger