Weargas, it does not have to be the actuator or the PCB. Boiler has preheat facility- that should be a clue.
There is NO thermocouple.
Can I suggest you call in someone who can fix your boiler. If you do this, you will not be changing parts needlessly. Ensure person who does call to fix your boiler ALSO does not rely on changing parts to effect a repair.
Initially I would steer clear of urge to replace the PCB.
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