Eberspracher temp control

Hi All. Hope you don't mind me coming on here as have a sprinter based Westfalia James Cook - used to have Westfalia Florida. I had trouble with the eberspracher on the Florida and am now having different trouble with the one on the JC. Think it is the same model D3l in both. Problem is that the heater doesn't respond to the temp control being changed at the Westfalia central electrics panel. Heater just blows at full heat all time. Eberspracher dealer had charged me a fortune to service it and swears it works as it should on the bench. Have changed the temp sensor inside the van. Can't believe it is the Westfalia central electrics panel ( a PCB) as all buttons work as they should. Don't know where to turn next so anyone out there with any ideas given that the Florida had a v similar set up as I recall it. Apart from the German JC forum not sure where else I should be posting either