Webasto FBH - Help me diagnose failure?

Hooked up the laptop for the commute home this evening - cleared the faults, but then got a new one "low supply voltage" the WTT software screen was indicating 6 or 7 volts. I guess this needs to be fixed before I do any PCB swapping. Luckily the PCB and gaskets on my spare FBH all look very reasonable. The combustion fan was cycling too, making the voltage change a bit.

OK so the PCB had died, new PCB installed by removing the wheel arch liner. While I was there I installed the Blue and Yellow wires which are needed for the remot control option.
Top tip - you have to remove the pink clip in the connector body before you insert the new contact. Thread the two wires into the engine bay, and secure to battery for now. The FBH starts by applying 12v to the Blue wire.

On the first drive with replacemnt PCB, The FBH kicked in, I set of driving, and the temperature gauge moved up to 12 o'clock position in around 5 minutes ! Amazing. 2 Hours later I started her up again for the return journey, and I started a stop watch at the same time . The temp gauge went from nothing to 12 o'clok in 4mins 47 seconds , much faster than I had seen before. I wonder how long it will continue to work for...