No D.H.W. for Ravenheat HE120T Low Nox Combi Boiler

16 Nov 2016
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United Kingdom

A week ago my mom lost all her DHW in the house. We discovered the boiler doesn't fire up when you turn on any of the HW taps. But she still has full CH control... and no error code comes up on the display

She had one plumber in who diagnosed it as a "Heating System Supply issue, possibly the DHW Sensor has failed" & quoted her £300 for job (for parts/labour). During the call out, though, he apparently spend a lot of time trash talking the Boiler to my mom (even calling it "a piece of s**t!") and said his company could install a new one for as little as £2,300 :mad::mad::mad:.
Being a little suspicious I wanted a second opinion, so I got another plumber in. He diagnosed it as a "Diverter Valve failure" & quoted £250 for the job (for parts/labour).

Could anyone give any opinion as to the failure please?
I'm disinclined to fork out that much (especially as my mom is a penioner), to either of them as neither sounded professional, and being an Engineer myself, their lack of professionalism (and courtesy) has me a little concerned.

Rob :)
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6 Mar 2003
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United Kingdom
I only have limited experience on a halstead boiler, but this is my understaning.
There are two circuits for the heated water. The circuits are separated by the diverter valve. The valve allows water to be pumped round the radiators for central heating.
For hot water, it is a case of cold mains water being fed into the boiler and coming out hot. To to this, there is a heat exchanger in the boiler and the diverter valve cuts off the heating circuit and pumps water around the heat exchanger, which then heats the the cold mains for the hot taps.

It basically functions as follows. The diverter housing has a rubber diaphragm with equal water pressure on each side.
When a hot tap is opened, the pressure on one side of the diaphragm is reduced and causes the valve to move across using rod connecting valve to diaphragm.
The usual problem of no hot water is the valve has not moved, or not moved far enough to make contact with a micro switch which is needed to light boiler.
Consider the following/
perferated diaphragm allows water to pass through so preventing or restricting valve movment.
Some improvment can be achieved by openig hot tap fully.
There may be some stiffness in the valve assemly
It could be the valve is operating as it should but the micro switch has burnt or dirty contacts.

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