A longer test today. Heat cycle works fine and first few vent cycles were ok but during venting, sensor data was corrupt. After approx 5 vent cycles, servo stalled. Quickly reset arduino and then servo performed well straight away.
I was reading up on the motor control shield for another project and it detailed the need for three suppressor capacitors on cheap dc motors. The servo I’m using is the Tower Pro SG90 – I think that’s cheap.
I’m now thinking of removing the vent flaps and replacing them with some forward facing ducts. This would do away with the need for the servo. I’ll think some more