Bang when turning on central heating

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When starting from cold, the heating is OK. After being on for about 30mins or so, I start to hear vibration sounds in the pipes around the boiler. If I stop the pump, and re-start a few minutes later, I get a bang in the system. My boiler is a Potterton.

Anyone know what's happening? I'm thinking that it could be the pump - am I on the right track?

Thanks!

Andy

PS. The bang doesn't come from the boiler as this is wall mounted away from the cylinder & pump. Instead is seems to eminate from the pipes around the pump.
 
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Turn down your boiler stat & see what happen and also how old is your pump?
 
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I tried turning down the boiler stat & it did not seem to make any difference. Not sure how old the pump is. Over 4 years though.

One thing I forgot to mention. The first hint I got that something was wrong, was that I got home from work the other day & the boiler had turned itself off via some kind of safety switch on the underside of it. I clicked it back in and the boiler started again OK. Is this to prevent the boiler from overheating?

I have the individual thermometes on each radiator & had turned 2 off with the weather being warm lately. Could this have cuased it?

Thanks for your help as I'm hoping to be able to sort this without a big bill from the local plumbers!!
 
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One of your radiator must not have a thermostat valve unless it is by-pass somewhere else and must be left open,if so this can cause kick back to the pump.Did this only happen when you turned 2 radiator off?

There can be many reason,pump on it way out, motorized valve sticking/jammed or sludge build-up which restrict the water flow or incorrect gas flow pressure or thermo coupling so boiler could need a service etc.

Does it still do it when it on hot water only ?

As a guess I think when your radiators reach the temperature setting on each radiator and your room stat is keeping the pump running therefore vibrate as it got nowhere to go which causing kickback pressure then your boiler start to overheat.
 
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I had the same problem: The pipes from the boiler were laid on top of oneanother and so the pressure when hot water started to pump would vibrate the pipes, banging them together. Mine was really violent and would wake me up at night. It was partly due to sludge in the system too. It was also partly due to air in the system.
A quick solution ,but only short term, would be getting your floorboards up and securing your pipes properly. Longer term replace the rads.
Temp was also a point. There was no thermostat on my hot water tank so my system would only boil the water, even with the stat on the boiler set to the lowest setting.
 
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uskys said:
I had the same problem: The pipes from the boiler were laid on top of oneanother and so the pressure when hot water started to pump would vibrate the pipes, banging them together. Mine was really violent and would wake me up at night. It was partly due to sludge in the system too. It was also partly due to air in the system.
A quick solution ,but only short term, would be getting your floorboards up and securing your pipes properly. Temp was also a point. There was no thermostat on my hot water tank so my system would only boil the water, even with the stat on the boiler set to the lowest setting.
 
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