Car's back to it's normal self now(95WRX), aside from one thing.
The heater comes on when the engine has a bit of temperature, and blows hot air when the temp is set 1/2 way (25?).
After 45 mins of driving, the blowers blow cold unless you turn the heater to max. You might think "well that's because the cabin is up to temperature", but that's not the case. You can open al the windows and get the cabin cold, and the heater will still blow cold.
I've checked the obvious stuff (no water leaks or air in the cooling system), it just doesn't seem to be able to maintain a moderate temperature once the engine has run for 1/2 hour or so...
The only thing I can think that would affect it is the fact that the AC needs vacuuming and refilling. Is that what's causing the problem?

 

Has it had the coolant drained? New rad? New hose(s)?

Sounds like an airlock to me.

 

Yup, coolent drained, but refilled as per the service manual. It uses no water, and engine temperature is consistent.

 

For what it costs ide drain and change the thermostat- could be sticking? For the sake of 20-25 quid it eliminates that

 

Drain it and refill it yourself after doing a search on here for how to, without airlocking.

 

Thanks for the advice guys, I'll drain the coolant check the thermostat and refill and see if that makes a difference....

 

DO do a search for how to...it almost impossible to "bleed" air out of the system once it's in.