heater!

[Tom mk2]

Hi all. just bought a G.reg mk2 gti and the heater doesn't seem to work. the thermostat was replaced a couple of weeks ago so can't be that not working. what else could it be?
Thanks

[Ben Lessani]

Air lock
Broken diverter valves
Dead heater matrix
Dead fan
Dead fan switch
Faulty water pump
Mouse stuck in matrix housing blocking air flow

Could be many, many different things. Get the car up to temp. feel the bottom rad hose to make sure its warm and the water is circulating. Then feel the inlet and outlet for the heater matix (the two hoses that go into the bulkhead), see if they are cold/hot.

If you still have the recall valves fitted that's probably why, whip them out, put in some copper pipe and fit a MK3 heater matrix whilst your at it and you'll be as good as new.

This has been posted 1,000,000,000,000,000,000,001 times - do a quick search and you'll be knee deep in answers

[Tom mk2]

fan seems to work because it will blow cold air out. car temperature is spot on so doubt air lock which leaves the heater matrix (common problem?) or the water pump!
cheers 

[Ben Lessani]

If your water pump isn't working, then it would be pretty bad. Start the engine, open the expansion tank cap and see if the rad return flow is constant and strong.

[Diamond Hell]

£10 says it's the stupid check valves that were fitted inline to the cabin matrix.

If you're happy the matrix is sound remove them. Heat will be restored.

[Tom mk2]

If your water pump isn't working, then it would be pretty bad. Start the engine, open the expansion tank cap and see if the rad return flow is constant and strong.

if it was the water pump would the car not be over heating? temperature seems to be spot on - square in the middle of the dial

[Ben Lessani]

If the water pump had failed - the temp gauge becomes worthless, the hotter water wouldn't be flowing by the sensor.

By the time the water has heated enough to transfer to the stationary water at the sensor, its probably too late

That's by the by though, I was just posting all the things that could cause no warm air inside the car

[Tom mk2]

ok, so if I open the expansion tank i should be able to see water flowing into it steadily?

[Ben Lessani]

Yup.

[Tom mk2]

yep thats all working just fine  cheers.