Hi, the contacts for the control at the rear of the dash wants cleaning, the air / heat mayby the heater control valve under the bonnet , Has the car run out of water at any tiime? thus causing an air lock? check your heater hoses under the bonnet to see if they are hot, check you have water in the system ( CHECK THIS WITH THE ENGINE COLD ) The thermostat may need replacing as it is not opening if you are handy at repairs this is not a big job but again, ( DO THIS WITH THE ENGINE COLD)