softus , tell em to test by substitution thats what ideal do throw a few parts at it one of them is bound to be right. and they make good money from the spares.
Pump over run stats have two positions , in it`s rest postion when power is supplied to the boiler the pump will get power through it straight away and start up then as the boiler heats up the stat then moves contacts to supply power to pump as long as heat is in boiler.
What happens is it sometimes does not fall back completely to rest position and isn`t making any contact so when boiler fires the pump is not getting any power so the water starts to boil and bang then as the boiler heats up the stat registers heat in the boiler moving contacts and supplying power to the pump.
Checked for voltage and yes there is 240V when it is ment to be running. The pump has a switch to select a speed. These are numbered 1 -3 and it is set on 2. When I switch this to other settings and back to 2 the pump seems to start. What are the settings for?
also What is the screw looking part in the centre of the pump for?
As a general rule pumps on system boilers and combis should be set to 3. This is the fastest speed setting.
It sounds as if the switch in the pump has broken, in which case replace the pump, as a complete unit. Make sure you give the boiler serial number to the parts supplier to get the correct pump. Ideal have a nasty habit of changing bits as the production line ensues.
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