Heater problem

[Mik]

Does anyone know how the heaters in R33s work?

Specifically, does coolant flow through the heater core whether the heater is on or not (and a flap in the heater box diverts the air around the core), or is there a valve in the engine bay which controls the coolant flow to the heater core?

My problem is that I recently removed my heater matrix because I thought it may have been leaking. It turns out that it wasn't leaking, so I refitted it, but my heater no longer blows hot air. Maybe I have an air pocket in the system?

I did a diagnostic and it only came up with a sun load sensor fault...this probably happened because the car was in the garage.

Anyone have any ideas?

Cheers