My Vaillant VCW GB 242 E Combi Compact Wall Mounted Boiler is failing to ignite when the central heating is switched on. I can hear the fan starting up but when i look in the combustion chamber there is no fire .
The hot water on demand is working fine.
Boiler Water Pressure around 1.5bar.
Can anyone provide any ideas as to the cause of this issue?

Khaled, November 2011

Generally speaking, the servo valve will be sticking (not returning) to allow the diverter valve to shut making both m2 & m3 microswitches. There are various possible causes:

Water section leaking through the stuffing box, causing the pin above to stick up in the sleeve.

Servo valve itself faulty (spring not allowing return).

Blockages in the small tubes to the servo valve (caused by dirt in the system).

Carefree, November 2011