Radiators "knocking"

[Arese]

Hi all

since we had a new boiler installed (condensing combi, Worcester), on the odd occasion we get a horrible "knocking" noise coming from one of two radiators. One of them is on the ground floor, the other is on the first floor. It's hard to describe, but it's similar to someone tapping a pipe with a spanner!

The noise seems to be coming from the temperature control valve, and if I adjust it every so slightly, the noise stops!

Also, the boiler tends to lose pressure over the period of several months, and I have to top it up manually. I assume the two issues are related.

Any ideas what the problem is? Air trapped? I've tried bleeding the radiators a few times, but it doesn't seem to help. Admittedly, I've not bled them all as one in particular is hard to get to.

Thanks for any advice.

[mycroft]

Some thermostatic valves are directional , the knocking is due to the flow going through the valve the wrong way . If you bleed the rads you are releasing the pressure in the system and will need to top it up . You shouldn't need to bleed the system on a combi .

[Arese]

mycroft said:

Some thermostatic valves are directional , the knocking is due to the flow going through the valve the wrong way . If you bleed the rads you are releasing the pressure in the system and will need to top it up . You shouldn't need to bleed the system on a combi .

Cheers mycroft. Ok, so if the flow is going the wrong way how do I resolve that?!

[homeimprovements]

Hi

If I were you i would call back the installing engineer and get them to put the TRV on the flow pipe or install some bi directional ones.
You could try to remove the head of the vavle as some have a plastic collar that you just rotate round to change the flow direction. As for the topping up of the radiaters do you know if any inhibitor was added to the system when it was installed