Heater blowing cold

[titaniumash]

Hi,
My heater has an intermittent problem where the heater only blows cold. It is a 2009 titanium with climate control.
When I first start the car it will blow cold with the temperature set to high then after a while it will start blowing hot. I have entered the hidden menu to display the coolant temperature and it gets up to temperature ok. There is no pattern at all eg I can be driving for an hour and it won't blow hot at all and on another journey it may blow hot after 20 mins.
I know the older models had issues with heater control valves but cannot find anything for my model.
Also my friend has plugged it into his snap on computer and it displays an error code B10B8 but I cannot find any helpful info for this code.
Also both pipes to the heater matrix are hot so assuming a dodgy flap motor?

Any help would be gratefully received.

Thanks