Heater Not Working After Head Replacement

[Prado_90 Lurker Find all posts View Profile Close Prado_90]

I have recently had the head, CAM belt, water pump and radiator replaced on my 1999 1KZ Prado. The heater worked before now it doesn't.
The hot water valve on the firewall in the engine bay is not opening. If I gently force the valve open the heater works.
If I put climate control in auto and then turn the temperature control valve to cold, the hot water valve on the firewall drives itself closed as I would think it should.

Is there a sensor on the engine they have missed when putting the engine back together?

Thanks