E70 n52 4 zone ac coolant pump and fan cycling.
 

My cooling fan and electric pump cycles on and off when engine lightly loaded and heater on. E70 n52 4zone ac. Note I have just replaced the water pump and thermostat. As the previous unit appeared to have failed (amber overheat warning and code) The ycling behavior (cycling pump and fan) is highly repeatable. If Iat idle i set the heater to 20 degrees everything behaves normally, turn it up to 21.5 degrees and suddenly the pump and fan start to cycle on and off. Any suggestions?

The replacement parts are they aftermarket?

Yes. Aftermarket parts. Thermostat is waller borg Warner. Pump is unbranded.