Fan comes on and burner pilot lights but boiler does not fire up. Checked Solenoid at 2.7k. Any Ideas ?

Daz, March 2010

Found the fault. It is the Mercury vapour valve which is at fault. In my days from working on gas ovens we knew them as FSD's . Thanks for the help guys. Got one off ebay for £30 Bargain !

Daz, March 2010

If you have a fan that starts up before the boiler ignites , then there is also an AIR PRESSURE switch.

The problem may be due to a partially blocked plastic pipe between the switch & fan.

It goes via an inline metal restrictor ( inside the plastic tube) that can block up.

Remove the tube and suck/blow so that you can hear the Air Pressure Switch clicking...then replace the tube.

A very common Netaheat fault....on these boilers with the fan + pressure switch !

Beware scrapping the boiler as most parts are still available (Ebay etc) so don`t jump to any expensive conclusions.
(and don`t believe what the CH engineers or Gas Board tell you. These old boilers are built to last....more than 28 years if necessary!)

chas, March 2010

I am an unqualified muppet with respect to boilers...

If the pilot light lights you can be sure that the fan and the pressure switch are working well.

If the main gas valve does not open - and you appear to have checked the continuity of its coil then what remains as probable causes are:

Pilot injector partially blocked failing to generate enough heat to activate the sensor.

Pilot flame sensor defective - not sending to correct signal to control board

Pilot flame sensor OK but control board failing to act on signal from sensor.

Good luck...

Peccavi, March 2010

sounds like pcb if the solenoid is opening, dont think you can get gas valves for these anymore, but they still make most other spares. could be a slow fan, see if it fires with the case cracked open also check the air pressure switch is making contact and releasing, ive given you the check order arse about face but, go through all of these and you will find the fault

john, March 2010