Vaillant VCW GB 242EH no CH

I have a Vaillant VCW GB 242, I had a problem with it leaking from the servo control valve. I removed the valve and replaced the diaphragm. I then re-assembled the valve and re-installed. Having done this the boiler would not fire up. I checked through the manual and it gives information on setting the micro switch, this involved disconnecting the micro switch and feed lines. When I put it back together it now moves the cam round and engages the micro switch so I get hot water from the tap, but I cannot get the CH system to run, I can hear the pump running but boiler does not fire, I have tried adjusting the "pin" that is pushed up by the diaphragm, as as I stated above I can get it to light boiler for hot water, but no what I do I cannot get it to light for CH, anybody got any ideas what I have done wrong?


Thanks Pete

make sure the cam is going all the way back or the diverter valve wont move

The servo valve (the plastic part with the 4 control lines) does not have a diaphragm. Do you mean the mean the water section at the front underneath?

Are you sure the adjustment is correct. If the adjustment is correct on the pin then perhaps the spindle into the servo valve is sticking. If the cam does not retract fully after DHW operation the differential pressure applied to the diverter will not be sufficient. If the diverter does not move fully to the left ? it will not operate the microswitches to fire up the boiler.

Thanks Guys,

Yes it is the water section underneath the servo valve, I fit a new diaphragm to the underneath, when I first started it up the boiler lit straight away without any taps on, so I removed the spindle that is pushed up against the cam and adjusted it, it now puts on the hot water, but with regards to retracting it does not seem to go very far back down, is the way to test the CH to remove pin and see if CH comes on without it installed? In the manual it says make sure servo valve is in CH position, trouble is I'm not sure what the CH position of this valve is, is it the complete opposite way from the micro switch, does it mean the pin needs to be at its lowest? I have also checked the water section with diaphragm fit and it appears ok.

Any help will be much appreciated.


Cheers

Pete

Is there a spring connecting the cam to the mounting plate?

Is the adjustment pin free to move in the sleeve in the mounting plate then runs front to back?

The cam should retract under the force of the spring and from memory with the correct adjustment there should be a gap between the lower edge of the cam and the adjustment pin.

There is also adjustment on the microswitch - it can be swung left/right to give the correct clearance between the metal operating lever and the cam.