Heater blows hot when moving and cold when still.

I've got a VW Transporter T5 1.9tdi and it's just started blowing cold air when it's sitting idling, but when I bring the revs up or drive it blows hot. When I slow down or stop at the traffic lights it goes back to blowing cold air.

The temp gauge sits half way like it always has done and its not the heater matrix because I flushed it out and it was fine. I am thinking water pump but I'm not 100% sure.

Asked on 21 November 2011 by jonnyboy16v

Answered by Alan Ross
Not sure why you think water pump. Would suggest that you re check your coolant level to make sure it is correct. Also what temp is the engine running at?

Also check the connections leading to the heater matrix, if there is a tap/switch (connection from the engine block) is that fully operational.

You may also need to check that the flaps behind the matrix are diverting correctly.
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