TRV's Knocking

[fordinio]

I have just had a new condensing combi boiler fitted, retaining the existing radiators and most of the pipework. When the TRV's are in the approx mid point setting the upstairs ones just randomly start knocking, presumably as they are about to shut off. The knocking is easily stopped by just turning the valve slightly one way or the other. There was never any problem with my previous 20+ year old boiler. Can anybody help please. It's driving me mad.

 

[stevetheplumber]

at a guess you have old trvs that only work with flow one way and the circulation in your system has been reversed

 

[Billy Bob Bob]

at a guess you have old trvs that only work with flow one way and the circulation in your system has been reversed

yep or they are faulty due to age better to replace anyway old trvs can stick get new reversable flow type