Boiler lock out after firing

[Incrisis]

Hi all

For background info, I have a Worcester Bosch Heatslave 20/25, it is at least 21 years old and over the years has had several parts replaced, also over the years it has gone through phases of constant lock outs, not firing etc, and I have used this forum a few times to point me in the right direction.

The boiler has ran fine for around the last 2 months, when I first started using it for heating this year, but today it locked out and when resetting it fires, runs for around 10 seconds and locks out again.
I opened the nut on the oil feed to the burner nozzle and it seems to have plenty of oil feed/pressure.
Water pressure is fine.
I have tested the flame sensor photocell by removing it and using a multimeter on the OHM setting, mine is at 200k setting, and it shows a reading when the sensor isn't covered and no reading when the sensor is covered.
I am not sure if the pump is running, I have used YouTube university to find out how to check it so may give that a go tomorrow.

Just wondering what else it might be before I call a professional to take a look, if I wasn't working 12 hour day shifts for the rest of the week I would have given them a call already but really want to see if I can sort it and not have to rely on portable electric heaters for the next week.

I have also started to request quotes for a new boiler, I know it will be expensive but I think it is about time I bit the bullet.

 

[Burnerman]

The photocell should have a very low resistance in full light and a very high one in total darkness.....maybe your meter doesn't read high enough?
Anyway, this is a typical photocell fault and is worth replacing - cheap enough to rule it out of the equation anyway.
John

 

[Incrisis]

The photocell should have a very low resistance in full light and a very high one in total darkness.....maybe your meter doesn't read high enough?
Anyway, this is a typical photocell fault and is worth replacing - cheap enough to rule it out of the equation anyway.
John

Thanks for the reply.
When I switched the multimeter to 2000k it did show a high reading in darkness and low when in light, I didn't think that was correct, especially as it was the opposite to what I seeing at 200k, but I did only go off someone on YouTube showing the same photocell and testing it.
I have ordered a new one, should be here in 2 or 3 days.

 

[Stuart981]

Could be air entering the oil feed.

 

[oilhead]

Have you tried firing the burner wit the photocell out, but covered and releasing to light when fired? If the burner continues normally, then further inspection of the flame pattern etc is required.
Have you tried the start up with a pressure gauge on the pump? It could be that the initial pressure dies off for lack of fuel. Have you checked all the filters in supply? Do you have a steady flow from the supply pipe?

 

[Incrisis]

Have you tried firing the burner wit the photocell out, but covered and releasing to light when fired? If the burner continues normally, then further inspection of the flame pattern etc is required.

I have just tried it using a torch to make sure there was plenty of light getting to the photocell as where the boiler sits is a bit dark, and it done the same, ran for 10 seconds and locked out. When the burner fired you can see the orange glow of the flame through the hole

 

[oilhead]

I would try a new photocell for what it costs before a control box.At that age, a boxand cell would only be about £50-£60. (i'm assuming a B11 burner.)

 

[Incrisis]

I would try a new photocell for what it costs before a control box.At that age, a boxand cell would only be about £50-£60. (i'm assuming a B11 burner.)

The photocell in it is a Satronic MZ770S, I ordered one from a plumbing and heating supplier, £15.39 including postage, hopefully will be here tomorrow or Thursday.
It is a B11 burner.

 

[Incrisis]

Update: I am still waiting for the photocell to show up, but today the control box was delivered,
Put the new box in place and the boiler is working fine.
I will probably keep the photocell when it gets here, no harm in having a spare.