Banging hot water pipes

[finman]

I have a baxi bermuda fire with a baxi bermuda 552 back boiler.When I have just the water on everytime the burner switches off I get really loud banging noises from my pipes.When water and heating is on it is all quiet.There is an elsan indirect hot water tank in loft and when pipes are banging water is spitting out of a u shaped pipe.(sorry I dont know correct name) Have I got air in system or could it be a faulty boiler thermostat.Thermostat doesnt switch off when water and heating is on.

 

[LUNAT]

HI


there could be several faults with your boiler.
1.radiators might need bleeding
2.boiler stat could be faulty causing the water to overheat
3.try setting the pump to number 2 (if pump fitted )

 

[bon98uk]

LUNAT's right there are several possible reasons for 'pump over'.

You don't say if it's gravity fed or fully pumped. Nor if there is a Motorised Valve on the hot water return.

I have had a very similar problem to this and I have traced it to faulty wiring. (Basically the boiler should not have a live electrical feed *unless* the heating or Hot water or both are calling for it. If this happens the boiler short cycles and the water overheats in the vent pipe causing cavitation and 'bubbling' over into the expansion tank.)

I stress this is not the only possibility and LUNAT's suggestion should all be considered and checked out.