The circulating pump is central to the system. The pump on a combination boiler circulates primary water around the heating system and also through the secondary heat exchanger to transfer heat to the domestic water depending on which position the diverter valve is in.
The pump consists of a motor housing which drives an impeller connected to a drive shaft. The biggest problem with motors is that they are put under undue strain and burn out, If the circulation of primary water from the boiler out to the system is restricted then the motor on the pump will start to become strained and could possibly lead to failure.
The reasons that a pump will fail could therefore be one or more of the following –
1- There is not 240V supplying wither the live or Neutral terminals
2- A faulty capacitor
3- The rotor shaft has seized or debris is preventing the impeller rotating freely
4- Burnt out motor windings
5- Worn out bearings
All of the above can be remedied if required. The key is to diagnose the exact problem in order to find a solution.