Boiler intermittent fault

[fixitflav]

I have an old Ideal SE50 which has an intermittent fault.

The burner sometimes fails to light, though the fan is running. I turn the control-stat down to minimum then back up, and it then fires, each time it's happened so far. It seems to be more likely to happen when calling for HW (it's a W-plan) though I can't see why that would make a difference.

I'm inclined to suspect dirty contacts in the control-stat. Can anybody please comment or think of any other explanation?

 

[CountryFan]

Sounds like a control fault

 

[fixitflav]

Sounds like a control fault

Within the PCB?
As a stopgap, and to see if it happens on CH, I've turned the cylinder-stat down to zero and switched the immersion on.