gillbrook11

Thanks, Gareth. Unfortunately tried that too, on both thermostats we replaced and both worked fine in boiling water. Not sure about a pressure build up but how would I test/find that?

Yes, have had it checked since and the car is running cold as indicated. They didn't know why and no faults were showing up. Very confusing.

I finally got round to changing the thermostat to a genuine one but unfortunately made no difference. Temperature stays just under 50 degrees. 

The replacement was a Serck thermostat

Hi

I have an A4 B8 2009. I have changed thermostat and sensor and still, my thermostat does not rise. On long runs, it might rise to 60/65 but very rarely. It takes an age for warm air to come in the heater (maybe 15-20 miles) and when it finally does come, it's nowhere near as hot as it should be even when set to HI. What am I missing?