The hot water pressure has always been weak compared with the cold water from the mains, but the boiler "valiant" was able to cope with it and start.
Now on Saturdays and Sundays the pressure of the mains drop as usual (bit I can't really tell if it is dropping more than before), I can't really see any difference in the cold water pressure. It looks like the water going through the boiler to be heated is not strong enough to start it any more. When I turn on the hot water, the boiler doesn't start, but if I push the switch in the boiler that usually is pushed by the pressure of the water, the boiler starts and heats the water.
Is there a way to increase the pressure of the water going into the boiler?
The next day after I posted my problem, the boiler worked fine except sometimes it takes 10 - 14 seconds for it to start after I open the hot water tap.
I will have a go at the diaphragm and the heat-exchanger as you kindly suggested.
Years ago I had a problem with the boiler and had to change the diverter. Funny enough, I opened the diverter later and found a lot of soldering pieces inside. I can only think it came from fixing the pipes for the radiators.
Thanks again and I hope the problem is the heat-exchanger, as it is easier to replace.
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