I have a baxi 105e combi. The pressure keeps dropping to zero overnight when the boiler is not in use. An engineer replaced the expansion vessel and no leaks can be found on the central heating system but the problem persists. Any ideas?
Baxi 105e pressure loss
- Thread starter embersr1
- Start date
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check the prv pipe outside 
Nothing is coming out of PRV, there are no visible leaks on the central heating system (it's been doing it for a while now so a leak would have been visible by now), there are no leaks from the boiler and when the isolating valves for the ch flow and return on the boiler are shut, it still loses pressure overnight. When the system is topped up, central heating and dhw work fine until boiler is switched off by the timer at night. By next morning, all pressure is gone and the boiler doesn't light although no fault lights are illuminated! Could it be leaking back into the dhw side from the ch side via the plate heat exchanger? As I said, there are no problems from the dhw side even after prolonged running of a hot tap. I'm confused, all this water being put into the system must be going somewhere and as stated before, expansion vessel is brand new, properly charged and staying so.
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