OK so I received and fitted the CAN wires that Martin sent and connected it back up to the FBH. Start diagnostics and connects OK with FBH and get live reading of supply voltage, temperature and flame detector. Click Park Heating....and nothing...no fans, no firing, nothing.... .
Ironically the FBH is behaving better than ever and no faults for some time, so the pressing need to use diagnostics has gone, but I would like to get this sorted as ultimately I suspect it has not permanently cured the problem.
I did notice that the temperature was high, about 45 degrees, since the FBH had fired on timer that morning. Did anyone confirm whether the CAN disables FBH burn once over a certain temperature? I'll try it at the weekend from cold to eliminate that as a source. I'll also double check the wiring.
OK so a bit of an update on this topic. The FBH in my MY12 has been misbehaving for nearly 2 1/2 years of the 3 years I owned the car. The symptoms were that the FBH would run, but continually restart, and then eventually would lock out with an over-temperature fault. I purchased the shop loom to attempt to diagnose it and couldn't get the FBH to run from that loom (the CAN wire update described in this thread seems to have fixed that problem for some but I haven't been able to verify that on my own setup yet).
Anyway, in the process of checking the CAN wire update I cleared the existing heater lock-out and then noticed over subsequent days that the FBH faults had magically disappeared. It's now been a few weeks and the FBH fires faultlessly on both timer and when the ambient temperature is low.
So knowing that most faults don't magically correct themselves, I joined some dots and realised that the introduction of the original problem 2 1/2 years ago and the subsequent magical repair BOTH coincided with replacement of the coolant expansion bottle
Let me explain more: 2 1/2 years ago I got a low coolant warning which turned out to be a saturated float in the bottle and I therefore replaced the bottle with the associated level sensor. I never realised at the time but this almost certainly coincided with the introduction of the FBH fault. The low coolant level returned a few weeks ago (again a float problem) so I replaced the bottle for a second time. Cue magically fixed FBH.
I don't know enough about the wiring in that area but I can only guess that the coolant sensor and the FBH communicate over the same piece of car loom and a suspect sensor in the coolant bottle was confusing the car over the FBH status.
Either way I'm totally happy that its all working again and just posting this in case anyone else ever comes across the same symptoms.
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