Shower waste pump

[mikegas]

Hi i had a fault on a shower waste pump today, customer said it wasn't pumping the water away, i realised that the pump worked fine if the stat on the shower was below 3 only when i set it above 3 did the pump start to fail. I thought it was the flow switch failing but after reading another thread im now thinking its just the feed temp to the shower is too low can anybody confirm either way? its mains fed mira flex