Vaillant VCW GB240H not working

[emin-j]

Hi, I have a Vaillant VCW GB 240 H it's about 20 years old and is not firing up, the heating was on and we were drawing off hot water at the time the boiler stopped working and it has not worked since.
Four years ago I fitted a new diverter valve ( complete with switches),HX,and DHW microwswitch to cure previous problems.
The pressure in the system is fine,the pilot light is fine,the pump runs when you put the heating on,the diverter plunger and contacts are working,the servo microswitch is working ( the arm with the spring attached moves and closes the microswitch when the DHW is turned on)but the boiler will not ignite.
Although the pilot light remains on could it be a thermocouple problem ? I haven't turn the pilot off and tried to re light it.

thank you.

Just as an update - I turned off the pilot light and it re - lit ok , what I have noticed is the lack of a ' click ' when manually turning the heating on.

 

[Agile]

Is there a black plastic disk like part at the front in the middle which rotates and operates a microswitch where there is circulation round the boiler. Its called something Germanic in the book.

If so is this moving on CH but not on DHW? If so does the boiler work if its rotated by hand until the switch operates?

Tony

 

[DP]

VCW 240 is open flued version of 242. There is no circular disc, it has a cam that operates to HW demand. This cam does not move for CH.

 

[emin-j]

OK i'll try that then.