Worcester Bosch 240 RSF not firing - again!

[DonDiy]

Worcester Bosch 240RSF combi boiler.
Soft water, high mains pressure.

I'll start by thanking everyone who has helped in the past to save me expensive call-outs.

Now here's the latest problem!
I replaced the pump head as suggested by KevPlumb in my last post.

(//www.diynot.com/forums/viewtopic.php?t=195322&start=0&postdays=0&postorder=asc&highlight=)

Easy job and I was quite proud of myself. Everything went OK, bled radiators, vented pump. Heating & hot water from the kitchen taps operating nicely. The cold pressure was about 1 bar and when operating was around 2 bar with no fluctuations.
All OK for a couple of days.
Then when running a bath, the water was initially hot and then cut out. Tried with all the rads off, but no change. Now the heating doesn't operate either.
So, although pilot light is on, it doesn't fire up when demand is created.
I've even removed the pump again to test it electrically but it's fine.


Once again I'm on the scrounge for expert knowledge!

 

[kevplumb]

did you check the auto air vent top left of boiler was open

 

[DonDiy]

Thanks for the quick reply.

I think I know the vent you mean, I haven't touched that at all. Could trapped air be the problem?

 

[BingoBongo]

manual overheat stat

take cover off red button left hand side

 

[DonDiy]

Not sure what red button you mean - if it's the honeywell reset than that's OK, it hasn't tripped.

 

[DonDiy]

I've also noticed that the green 'demand' light on the front panel does not light up regardless of rad positions or hot water demand
Could the diverter diaphragm or microswitch be the problem?
Thanks