Hi need a little advice got a 2009 R-class now the weather’s taken a turn for the worst. Set the heater control to max and blower on medium. Clears the windows when frozen brilliantly. But some 20 minutes later the heater is not as hot as I would expect it to be. I’ve checked to make sure there is plenty of water in the header tank, which there is. Only had the car since April. So heater controls have been set to cool looked in the manual and setting seem to correct. I’m I missing something here, or is there another underlying problem that I need to be checking many thanks in advance after reading a few more post it appears my car could have a heater control valve connected to the heater matrix at the bulkhead. Is there a way to test this..?