losing water pressure in central heating system help

25 Mar 2005
Reaction score
United Kingdom
Problem in central heating system for weeks now cannot find leak losing pressure constantly anybody out there ever experience this plumbers can find nothing had thermal imaging detection system come in to evaluate cannot pinpoint leak help
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What type of boiler, what type of pipework(copper, plastic), how old is the system and has anything been added or altered in the system.
system 4 years old copper piping have to check what type of boiler as I am not on site right now tried sealing leak with a sealer flush lasted about 3 weeks then failed lost pressure again. There is one radiator not working in the house
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Firebird Oil fired
Closed system under 1 bar pressure
Loses pressure when cold
No changes recently
Started In january
The house is divided in 3 independent zones and we think we have identified the zone
added a non return to the water feed to the heating system
House is in Ireland
right, is the fill loop still connected, if it is disconnect it there could be something in the non return, expansion vessel check it's pressurized, check for weak safety blow off, check all rad and any other valves visable and nip up, if you can isolate each zone in turn then check again. Could be a faulty joint under floor or the dreaded nail. i'm afraid it's like looking for a needle. one other thing check if you can inside the combustion chamber of the boiler it's possible there could be a leak in there and the water vaporises when the boilers on.
if this is a typical installation in a external boiler house you may find
1 the boiler has not been serviced
2 the safety discharge may not be fitted/run outside
3 the expansion vessel is undersized.you need to look at the gauge and see if it rises as the water is heated.most likely place is the s/r valve or the aav .

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