Instead of hijacking multiple threads I thought I'd start one to capture it all

So I have a UK 2014 V8 diesel bought 3 years ago. The climate control in the cabin has always been a bit cold, but lately I've had enough! The rear passenger foot well has always been cold - JLS here suggested a possible flap issue? The rest was warm (I'm sure of it) but isn't now. I wondered if maybe the FFBH valve needed replacing, maybe recently failed, or the system needs bleeding.

I'll describe the situation and hopefully some guidance is forthcoming. It's 4 degrees outside.

I've had the car running on the FFBH for 30mins then I started the car and left it ticking over for 30mins (not ideal but I have no journeys to make!).

After this period if I set all dials in the car to 28 and "auto" the situation is as follows. My coolant light has came on and I topped it up prior. I do have a small coolant leak, and the rear coolant system has been looked at whilst resolving the leak but in the end it was a pipe in the engine bay.

Basically the only warm air (not 28 degrees but is warmer than any other) is the rear O/S floor vent. Almost everything else is cold or ambient (still cold due to outside temp).

Despite thinking it wouldn't fix it, I bought a cheap changeover valve, spent the day stripping, swapping and rebuilding. Followed by fixing the brittle plastics I broke in the top hose assembly (FFS!). Once all back together (bleeding was very easy) I am happy to report I have heat.

Needs more testing but was warm Vs nothing previously.

Now though my webasto FBBH didn't work from the fob, but timed does.

Maybe low battery in the car, so will test once being used again.