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Combi Boiler Pressure at zero when not operating?

I recently had a repair on my combi. The hot water kept going cold - not very pleasant when taking a shower! The corgi man came and changed something which cost me £257 and then a couple of days later it still did the same thing. He came back and fixed it again with another part a thermistor, I think. That cost me another £50. Do they know what they are doing? Now the boiler pressure goes down to zero when it is off but when it is operating it goes to just above 1. I fill it using the tap. I once discovered a lot of water on the floor as though it had over pressurised. Is it normal to go down to zero when off or have a got a leak somewhere I don't know about? I've looked at all the rads and they are not leaking.

Marion
October 2009

Heating, Oil Filled Radiators Combi Boiler Boiler Pressure Leak

Thanks for your answer John. When you are ignorant about something, you trust people who are supposed to be "experts" but I think they just try new parts until they find something that seems to work but. of course, I am the one who has to cough up for all the parts and labour. Sometimes I think, although expensive, I may be better off going for one of those insurance schemes so that they come out quickly. How much approx will the job you describe cost me?

Thanks

Marion

Marion
October 2009

Hello Marion
First, change the boiler man. When you have found another, ask him to pressurise the expansion vessel, when it is empty, up to 10 psi. When that is done, the whole system should be filled to about 1 bar and the boiler switched on. Expect the pressure to rise to about 1.3 bar after a while. The pressure should remain constant. If it doesn't, there is a leak somewhere, so check the overflow outside before panicking.

John
October 2009