My pump is making a humming or buzzing noise. What could be the problem?

The most likely cause for a humming or buzzing noise is that the pump has seized.  This will probably be because of one of two things:

Hot water – The installation guidelines recommend that the temperature of the water going through the pump shouldn’t be any higher than 60°C.  This is because some of the components within the pump can be damaged by hot water.

Air – Excessively hot water bubbles, and generates air.  Air can damage some of the components within the pump, particularly the impellers that drive the movement of the water.  If they aren’t moving then the pump may seize and a humming noise will be heard.