Knocking Radiator

7 Dec 2006
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United Kingdom

The radiator in my son's bedroom starts making loud knocking noises approx. 1 hour after the central heating has been turned on. We have to turn the upstairs thermostat down to cut off the supply for it to stop.

The radiator sounds as though it is only partially full of water as you get a kettling effect when the heating is turned on like a kettle boiling. I have tried to air the radiator but even when all of the air is released, no water comes out. We also have a radiator in the back bedroom which does not make knocking noises but is not as warm as the rest of the radiators in the house. Again, I have aired the radiator but no water comes out when all of the air is released.

Can you let me your thoughts.
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if no water coming out it may want the system topping up if a sealed system or may be the header tank is dry or blocked cold feed. take your pick
Hi, my system is a Santon Unvented Premier Hot Water System. Not sure how you top the system up.
So what boiler is feeding your heating? That is if it is seperate?
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Hi, the boiler is a Ferroli Sigma Boiler. A couple of people have mentioned it could be a blocked cold feed, is this easy to fix?

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