Riello burner won't fire up

[DAVID FINLAY]

Our Riello rdb2,2 26-33 burner won't fire up, there is no wall mounted thermostats, it is about 7 years old and our house is very thermally efficient, so there is 600 litres of oil used over a year. Two weeks ago the burner was running to heat some water without any problems. The other day when I switched it on the fan was running but it didn't fire, the red button doesn't light up and I have tried the small overheating reset button to no avail. I have pressed and held in the big red button several times, checked connections and cleaned the flame detector and shone a torch on it, I have even borrowed a black control box, but no joy.
Does anyone have any ideas that I could try?

 

[Exedon]

If motor is constantly running and not going to lock out photocell normal candidate but really you shouldn't be trying to change random parts. Decent oil service engineer required!

 

[DAVID FINLAY]

Thanks for your advice, I am a mechanical engineer and I only changed a ''random'' part because a working control box was available, which ruled it out as being faulty.....

 

[oilhead]

Unplug the photocell from the control box. Start the burner, if it fires then goes to lockout, replace the photocell.

 

[DAVID FINLAY]

Oilhead, your advice worked a treat, thank you. Now I know what part I need.