Well at long last I found the cause of the heater only blowing on 3 and 4, it was the heater fan control switch. However it has literally melted together with the connector and the switch had to be broken off (took ages!).



Well I'm a bit stumped now. I've got a new control switch but as you can see the connector has had it. Has anyone had this problem before?

It would be nice to have a heater which worked on all 4 settings!