Vaillant ecoTEC plus: water heating works fine but the central heating will not switch on - there are no error messages. Checked the remote and this seems fine. Tried the manual timer and this also does not switch the central heating on. Any suggestions as to what the fault might be?

LeBr5, April 2010

On my Potterton Boiler and on many others I suspect - when in Central Heating Only mode - the Fire Up signal to the boiler is routed from the Timer Programmer - to the Room Stat and then to the Mid Position valve - when the valve's motor has moved the valve to the Central Heating position a microswitch is activated which sends the fire up signal to the boiler.

If you have a MVP in your system you should hear the motor running for a few seconds when CH only is selected - there is sometimes an override lever with the ability to latch the valve permanently in the CH position I believe.

http://www.wickes.co.uk/content/ebiz/wickes/invt/443033/3-Way-Mid-Position-Valve_large.jpg

I am not qualified or experienced in boiler maintenance - my advice is worthless.

Good luck...

Peccavi, April 2010