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Make sure the vent damper is fully open. Next take a clear, well lit and well focused close up photo of the wiring diagram glued to the inside of the boiler service cover and post it here using the paper clip icon at the right end of the tool bar above your dialog box.
Tell me a lot about your technical skills background and if you have a multi meter or not, we can go from there.
tell me what you can discover, we can go from there.
If the vent damper is closed the boiler will not fire, check for voltage to the vent damper motor, it you have voltage and the damper does not open, then the damper motor is bad.
If you have no voltage to the damper motor then the we need to follow the wires back from the damper motor to see what switch is open as shown on the diagram I marked up.
If the damper motor is indeed open, you will have to check that physically, then there are two additional wires running to an end switch in the damper motor that close when the damper is open... the boiler will not fire until that switch closes.
I see you have requested a phone call, I will send you an additional service offer, if you accept I will send you my email address and you can use that to send me your private phone number, do not post it to this dialog box, anything posted is not private and is accessible world wide.
I will be up for another hour tonight, if I miss you I will be back in the morning and we can go from there. You do not have to accept the phone call offer, you can also just do the tests prescribed and we can continue in this dialog box at your original offer amount.