Oil-fired boiler fires, runs for 75 seconds, cuts out....

[simonlord]

Worcester Danesmoor from 1996, serviced earlier this year. Fires, but the lock-out light comes on after about 75 seconds. Slight change in the firing noise about 15 seconds before the light comes on. Plenty of oil in the tank. Lock-out can be re-set after a min or so, and then it goes through the cycle as above all over again.

Ideas? Many thanks in advance.

 

[dontknowitall]

Possibly the solenoid valve not opening. If there's a good roar (flame established) then the photo resistor.

 

[stevetheplumber]

Possibly the solenoid valve not opening. If there's a good roar (flame established) then the photo resistor.

have you checked the pump is working if its fully pumped heating and hot water

 

[simonlord]

Pump is running fine - but the solenoid coil went before, I remember, and seems to be a weak point on these.

Flame establishes as I'd expect about 6-7 seconds after the fan starts up, and then cuts - last attempt was after 2.25 mins, so I'm suspicious of the flame photocell. I took it out and cleaned it, but I guess there's a window into the burn chamber that could be sooted up?

 

[Puddle]

You say a slight change in burner sound just before cut off, ,simple checks first,have you replaced inline filter recently ,possible blockage in filter ?

 

[dontknowitall]

Still sounds like the solenoid to me. There's no window, just a hole for the photocell to see the flame. You could possibly test the photocell by taking it out (which will produce a lockout). Time the boiler from activation to lockout a couple of times. Then when you replace the photocell, time it again. If timing to lockout is still the same, probably the solenoid. If different (longer) then probably the photocell.

Sequence is (Flame not established on start up):

Thermostats call
Motor and ignition on
Solenoid valve opens
No flame
Photocell sees no light
Motor/ignition/solenoid off
Lockout

Sequence for flame failure when running:

Run position
Flame failure
Photocell reacts
Motor remains on - solenoid off
Ignition restarts
Flame established?

No - Lockout
Yes - Photocell reacts
Ignition off
Burner into run position

Worcester's number is 01905 750624 or 08705 266241. Very helpful and friendly.

 

[simonlord]

I removed the photocell from the chamber and blocked the aperture, and it wouldn't fire/run at all, so it seems the photocell is working, which tends to point to the solenoid, I guess?

 

[dontknowitall]

I think so, especially if it's failed before.

But removing the photocell would stop it from running anyway as it can't see a flame. This is why I suggested timing it until lockout without the photocell. Then trying it with the photocell to see if timing to lockout is different.

Just in case you're not aware ... The photocell is a safety device. It looks for a flame and if it can't see one it triggers the boiler to stop - and as a result to stop pumping oil to the nozzle. So long as it can see a flame as far as it's concerned the boiler's okay to run.

Hmmm - just had a thought!!

And hopefully I've got this bit correct ...

The solenoid asks for oil. If the pump is giving the solenoid oil then the solenoid opens it's valve and lets oil through to burn. If the pump has failed the solenoid won't be receiving oil so won't let the burner turn on and a lockout will occur.

Maybe the pump? Try Worcester?