My Vauxhall Corsa 1.2 heating works intermitenly. I can work very well for about a week and stops working for another. I also have the same issue with aircondition. the problem has been going on for about 6 months now.
Intermitante faults in the heater are normally caused by an Air-Lock (If you're not refering to the blower)
The cure is to bleed the system, this can be done either by taking the Return hose (Not the flow) off and running for a few minutes steming the flow with your finger, or some models have a bleed screw in the engine compatment.
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