The hot water on the combi system fails to come on - but not all the time, sometimes it does but goes off again. The water pressure is OK and a new circuit board was fitted about a year ago. any ideas?

Eric, January 2009

I have the exact same problem with mine and spoke to Vokera.

The Domestic Hot Water (DHW) part is triggered by a diaphram valve which "senses" a tap opening and uses the mains water pressure to push on an arm to operate both the diverter valve and a microswitch to fire the main burner. The diaphram inside the valve is apparently renowned for failing, meaning the arm doesn't get pushed enough, or by a consistent amount. Its a really cheap part (

Craig Shearstone, February 2009