Been chasing some heating issues on my 4.4 tdv8 for a few weeks now.
FBH has never done anything. Even after running several times back to back.

Changeover valve was fixed as after summer had no heating at all.

More recently the passenger side got warm but drivers side cold.
The rear zone climate was also often blowing cold only.

I changed the dual solenoid this weekend and it made a little difference. The rubber was starting to break down inside.
I flushed the front matrix today, again a slight improvement but still not great.

I did a scan with IID and got B12A6-15 Auxiliary heater water pump - general electrical failure - circuit short to battery or open.
I haven't looked at it properly but I have felt it *operating* in the past.
How reliable are the pumps?

Would explain many of my issues.

To follow on from this turns out despite ruling out the crossover valve as I had only a few months ago repaired it, it was still faulty.

I repaired again and everything seems to be back to normal.