The most likely cause seems to be a failing heater control valve which sits on the passenger inner wing , there are some very cheap ones on ebay Circ £25 new which I will be avoiding after buying a dud throttle valve last time which didn't work for my dpf issue. Going of genuine ones on ebay it seems the dealer would need 400 quid ! for a plastic valve but Autodoc has a Bosch one for a more palatable 100 delivered.
In other news after getting our ds3 mot yesterday I took a late cancellation and get the x5 mot'ed last night ..Result as otherwise the next date was mid September (waiting times are going back to months here in Northern Ireland again for the umpteenth time )
That's 3 of the fleet through mot in 7 days 