Webasto C causes problems

Hello people, have problems with my Webasto, during the last test run at the beginning of December she ran still normal. Yesterday morning she jumped on but ran only about 5 -6 minutes.After run out of the water pump, restart and again the same. Three – four times tried again, same result. Today again tried twice from the exhaust, gas tank for petrol and ran again like gwestern. Again try, she jumped on ran about 8 minutes and end. BUT at the last attempt I sat in the car and put The blower went on and put out twice very briefly and ran on and put out after about 10 minutes, further par minutes the heater still ran and then switched off. My suspicion is the cause of the problem is that the blower shuts down,but why? Does anyone know advice ? Greetings Caravan-22