baxi 105e - ch pressure up and down?

[paulebble]

Hi, I hope someone can enlighten me?
I have had my boiler installed for 5 trouble free years, but recently the ch side was showing low pressure when the heating was not on. I topped up the boiler and left it. When I went back to check later when the ch was on the pressure was over 2.5? I checked again when the ch was not on and again the pressure was down??
I have checked the radiators and cannot find any leaks and cannot see any signs of water seapage on any ceilings or floors where the pipes run.
I don,t want to keep topping the boiler in case it goes totally over pressure.
Any help will be gratefully recieved.
Many thanks in advance
Paul

[bmcc]

Hi Paul i'm affraid i have no answer for your problem but can say i have the same problem.So far i have checked under the floor boards for leaks and at the moment in the proccess of checking the upstairs pipes and like you i can see no water damage to the ceilings.One leak i did find was a the top of one of the radiator valves but only a slight leak which i have cured by tightening the nut.I note on another thread that the 105e has a problem with a leak from the expansion tank ,I have checked in my boiler and don't see any signs of water escaping. Hope someone can put us in the right direction.
bmcc

[htg engineer]

check for leaks on boiler, pipework and radiators. Also check pressure relief discharge pipe as the pressure relief valve could be passing.

If the boiler pressure is rising to 4bar then this will operate the pressure relief valve and the water will be discharged to outside.

There's only a couple of problems that cause the boiler pressure to rise - the plate heat-ex may have a hole in it - or the espansion vessel need re-pressurising or renewing.

To test - turn off the cold supply to the boiler and run the central heating, if the pressure rises too much (0.5 - 1.0 bar is expected) then the fault is with the pressure vessel. If the pressure doesn't rise until the cold water is turned back on - you need a new plate heat-ex.