Heater issues !!!!!!!

[Deano2711]

I have recently bought a 1.8 20v Non Turbo. Drove approx 50 miles to fetch it. Driving back I went about 10 miles with no problems, the temp guage was stuck at half way as it should. Pulled into services to get some fuel and as I came round the slip road towards the garage noticed steam coming from the header tank area. Temp guage was still stuck at halfway. Spent about an hour on the services letting the air out of the header tank pipe, topping up with water and massaging the pipes. Carried on driving back about 25 motorway miles and 12 miles of town driving with no issues whatsoever. About 3 miles from home the low coolant warning buzzer went off so I stopped straight away and refilled. Drove home and when I stopped the steam was back from the header tank overflow pipe. Forgot to say all this journey I had the heaters burning my face off !!!
Next day I disconnected the top hose from the rad and ran the hosepipe through for a good ten minutes then popped the hose back on and started the engine. No heaters but also no overheating and no steam. Ran the engine for a good 40 minutes and another couple of 30 minute sessions but no heating. Took it to work Friday afternoon about 4 miles each way with no problems whatsoever but still no heating.
So today I disconnected the bottom hose by the alt. Ran the hose through for a good ten minutes with the engine running and the heaters on full. Reconnected the hose and left it running. Now I have no movement above half way from the temp guage still and my heaters are now blowing hot through the outer two vents on the dash but the two middle ones are blowing cold (not stone cold but nowhere near where they should be). When the car is idling there is steam coming from the overflow pipe. The top and bottom hoses are a bit stiff still. When I stop the car you can hear some air in the system still but if I remove the header tank cap after the air has stopped coming out then the pipes will become squeezable again.
I originally thought of the thermostat but if the water is getting to the heaters then that cannot be it. Same with the water pump. I just think I have an air lock somewhere but has anyone got anything else they can add or tell me the best way to sort this.  Any help greatly appreciated as I feel like taking a big hammer to the bloody thing !!!!  lol   

[Wazzzer]

is there water coming back into the header tank from the small top pipe?

[Deano2711]

Yes Mate water is coming back ok. All seems to be as normal except for the pressure causing the steam. I have flushed the system twice now. Just been to fetch another header tank cap from the local scrappie and that's made no difference. Really annoying me now !!!!!!!

[Deano2711]

Come on Guys really need some help with this one. I have now changed the thermostat and followed the how to guide on here. All went well until holding the revs at 2000rpm and waiting for the heater to start warming up. My expansion tank was getting lots of air coming back and was bubbling like a kettle. Eventually this died down and the cap went on. Heaters are working on the two sides but not the middle still. Within 2 minutes of the cap going on the top and bottom hose were solid.....is this normal as I have never checked to be honest ??   Will be taking it out for a little test drive very soon to see what happens but I am very close to smashing the bloody thing to pieces 

[Deano2711]

Forgot to mention that while I had the top and bottom hoses disconnected I have checked that the rad is not blocked with a hosepipe and checked that the water will pass from the one ond of the engine to the other easily. Will also get from the expansion tank to the engine block easily. The return pipe is clear and the water returns to the expansion tank as it should.   Really at a loss now and pulling my hair out.

[Wazzzer]

thermostat? Water pump sounds good as you have water returning to the header tank

[Deano2711]

thermostat? Water pump sounds good as you have water returning to the header tank

Water pump and head gasket seem fine, changed the expansion tank cap and thermostat, flushed the system three times now and contacted the twit who sold it me as a perfect runner !!!!!!!

[Wayne]

Not good then deano 

I guess it could be airlocked but it should have cleared by now.

[Deano2711]

Not good then deano 

I guess it could be airlocked but it should have cleared by now.

Tell me about it Mate.....I have never encountered anything like this before !!!!!  Got to be something really stupid somewhere....but where ??

[AudiA8Quattro]

If the system is pressurising all the time and you're sure the system is bled, then its either a faulty cap or headgasket problem.
What you need is a pressure tester like i've got, not cheap though, about 90 quid, but it will bleed the system in seconds.
I assume the top point of the system on the mk4 is the header tank, so i assume you have run the car fast idle with the cap off for a good 5 minutes.
How are you sure the headgasket is ok?