Heater not working, vx

[orthas]

Hey all
The heater in my vx is blowing cold air on the hot setting, I have been reading the forums here and tried a few things that other posts have suggested. So far I have replaced the radiator cap, heater tap and thermostat, bled the system a few times.
But now it seems to be running a bit rough, the temperature is going just over half every now and then (not over heating) and it will blow warm air when I accelerate for a bit but then go back to cold once running normally.
Any suggestions as to what it could be?
Thanks

 

[BOR15]

i would try flushing the heater core. it could be blocked. start with low pressure and watch what comes out the other side. flush also in the opposite direction.

 

[rambunctious]

The heater taps work on vacuum so check you have fitted the tap correctly, also check you are getting vacuum at the tap when the dash control is activated.

 

[BOR15]

i believe that with no vacuum the tap defaults to a flow state that directs water to the core.