I've replaced the mono valve and the CCU, still no heat.
It blows correctly and switches direction fine.
I'm out of ideas.
The only thing I can think of is when I replaced the monovalve, I undid something on the fire wall. I didn't reconnect it as it didn't look connected before and I couldn't see where to plug it in (see pics) the only other thing I can thing is that the mono valve may have been put back 90 degrees out, I don't know if that would do it.