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Hot Air Problem After T/stat Housing Replacement


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Hi all,

couple of weeks ago I noticed that the heater in my T reg 1.25 ZETEC was blowing cold with hot selected, this returned to normal after a few miles & I thought no more of it. 24 hours later the temp gauge hit the red as the car had developed a coolant leak. Eventually traced the leak down to the thermostat housing ( part of the o ring seal locating flange had disintergrated, un seating the seal ). I changed the housing for new but when starting the engine & up to normal running temp there was no hot air at all. Bled the water system to no avail. After about an hour took it for a spin, gave it a good booting tbh & hey presto heat came through, then faded back to cold. This was yesterday, went for a run today and heat came on as normal & got nice & warm but after about 5 mins went back to cold but sporadically warmish/ hotish air kept fading in & out. Coolant level is normal, temp gauge sitting halfway as it always has done. I had a look at the heater control valve & after just touching one of the hose connections the plastic neck the pipe connects to just "broke off". Im going to change the valve but not sure if this is the cause of my in & out hot/cold air problem. Someone has suggested head gasket failure but there are no other signs of this ( over temp, mayo etc ). Anyone got any ideas? Can find plenty of threads with either constant hot or cold air but nothing like this. Thanks for reading.

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I think your HCV is the best bet. It is such a common problem. This may have caused an air lock initially after you had replaced the stat as it would have needed to be open to bleed the system properly.

The only other thing I have experienced is the heater control panel behind the heater control knob packing in. But first I would change the HCV and maybe also the expansion tank cap to ensure the system pressurises correctly.

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