Noisy radiators

[julieee]

I have a problem with my pipes!
After the radiators have been on for about an hour or so a knocking starts which works its way from the boiler through the kitchen and finally ends up at the radiator in the lounge. On my dads advice I have bled the radiators (twice now) but it hasnt stopped the racket. I think that my neighbours must wonder what all the noise is. Help, can anyone solve the problem Please?
I have had a new combi boiler fitted but the radiators are old could this be why?

 

[gas4you]

Have you got thermostatic valves on the radiators?

If so do they have 2 arrows on the valve body meaning they are bi-directional flow?

If they only have one arrow or are old trv's it could be the flow is in the wrong direction since your new combi has been fitted and the banging you hear is the trv/'s closing down as the rooms reach temperature.

When you hear this banging go to the rad you think is causing it and open the trv fully and see if it stops.

 

[julieee]

Bit of a novice with radiator etc knowledge and talk , but by the thermostatic valves do you mean the part to alter the temperature to each radiator? if so there is an 1 arrow pointing down, these are on the right side of each radiator, you said about turning the valve, do you mean those ones?

 

[gas4you]

Yes. With only one arrow these valves will be directional, ie water must flow through them, in the direction of the arrow.

When the banging starts turn the numbered head to the highest number and see if it stops.

If so your installer has swapped the flow and returns from the original installation

 

[Agile]

More likely to be he does not have an auto bypass valve.

Even thats not the end on the story as I fitted a cheaper one recently and its quite noisy on pump over run.

Tony

 

[julieee]

Update
Put the rads on last night, once again after about an hour the knocking started, so i did as you suggested and turn thermostat on that particular rad and...Hey presto it stopped and didnt occur again fingers crossed it has stopped for good, or do you think that was just a short term solution

 

[gas4you]

It will occur everytime that you set the trv head to anything other than full.

You need to get the installer back to correct his mistake of connecting the flow and return off the boiler the wrong way round