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Cold water pressure ok, but hot water pressure not strong

Postby babboor » Sun Oct 03, 2010 1:12 pm

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?

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Simply Build It

Postby htg engineer » Tue Oct 12, 2010 6:54 pm

Check all isolation valves are fully open, also if the boiler doesn't operate then the diaphragm in the diverter needs replacing as it will be stretched or split.

The problem with the flow rate could be a scaled up plate heat-exchanger you will have to remove to try to clean - but not very effective you'd be better off replacing if it's full of limescale.

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Postby babboor » Sun Oct 17, 2010 9:02 am

Thank a lot htg,

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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