heater works on full but when turned down to three quarter position it blows cold air not warm air.just had engine rebuilt and the heater worked great before.could it be blocked and need flushing through, or how do you get rid of air locks.
if you look under the bonnet up towards where the wiper motor is you will see the heater valve, this is electic and is notorious for going duff the only way to fix it is to replace it @around £25
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