Alpha Ocean not firing.

[xanthophile]

Hi, Alpha Ocean 240E won't fire on DHW or CH.
I have amber warning light for 'Blocked flue or fan fault' coming ON whenever I demand DHW or CH.
I'm working my way through fault finding flowchart:

Turn selector to DHW. Power light comes on? YES
Turn DHW stat to max and open DHW tap. DHW switch operates? YES
Primary water diverted from CH to DHW heat exch? (DHW lamp on?) YES
Pump runs? (Judging by system pressure guage increase by 0.25 Bar) YES
Primary flow switch operated? APPARENTLY NOT. Disconnected wires and switch gives 13.5 kOhms whether DHW demand or not. When I short out towards PCB, nothing happens, however, I get what sounds like pump run-on for a few mins when I REMOVE the short.
Also, even though the fan is chucking air hard out of the flue, I get no 240V coming back from the air pressure switch.

I decided to stop there and seek your advice as these fails could be interdependent.

 

[xanthophile]

Tried a mains-off-and-on and IT'S FIXED IT!

Pity I'm too late to buy a lottery ticket - I feel very lucky tonight.
Perhaps I should go on the pull...