vaillant boiler - problem with heating

[landlubber]

I have a VCW GB 242 EH boiler, the hot water works fine, but the heating is intermitent.

Sometimes it works normally, other times it does not fire up when switched on, sometimes the heating comes on after running the hot water for a short period...............about a kitchen sink full!

any ideas as to what is likely to be wrong?

thanks in anticipation
landlubber

 

[Gasguru]

Have a look at the diverter valve on the right. Take off the transparent plastic cover and see if the microswitches operate as the diverter moves left right (and vice versa) dependent on DHW/heating demand. Don't adjust the switches but post back results.

 

[Deleted member 105431]

servo valve most likely. call vaillant for a fixed price repair would be your best bet.

 

[spacethegas]

the 'cure' will be too involved for diy.

 

[landlubber]

dear gasguru, sorry about the time to reply, had to work on the car, new track rods ends and balljoints to pass the MOT.

I have now checked the switches as you suggest.

When DHW is demanded the valve operates and the contact screws come out clear of both switches. I have run it through sveral cycles of DHW on and off and when it is turned off it returns to its "in" position and sometimes operates both switches but sometimes only operates the bottom switch.

When it contacts both the heating kicks in.

regards
landlubber

 

[spacethegas]

see all those tiny little tubes. there is probably some muck stuck in them.
they should be checked/cleaned. also so should the servo valve (black & white plastic bit with four tubes entering it) & the pressure differential valve (black plastic bit with two tubes entering it) while you're at it. + the automatic air vent must be in good nick.

good luck if you fancy tackling it.