New Central Heating System - Knocking sounds in the wall

chris1012

We had brand new cebtral heating in the house 3 months back and we didn't really use the central heating until the last few days.

Since using the Central heating we can hear are a very frequent knocking sound in the wall.

There is no way to access these pipes to check unless we break tiles in the bathroom or make a whole in the newly painted living room.

What do we do to identify/resolve the fault?

Myser

Do those pipes lead to a radiator?

It could be a stuck TRV (Thermostatic Radiator Valve). Try turning the TRV head in one direction and then the other to see if the knocking sound goes away.

chris1012

They do lead to a radiator with a TRV.

The knocking went away again but tends to come on during the first bhr of the heating being on.

How is this related to the TRV?

Myser

If the knocking disappears when you adjust the TRV, either it is not fitted to the correct side of the radiator or it could be a cheap TRV.

Many modern TRVs are reversible and can be fitted on either radiator pipe. The older ones and some modern ones can't.

You can also get knocking from cheap TRVs hence, why I asked if it disappears when you rotate it?

Is the sound definitely knocking and not a whooshing sound like trapped air?

Have you vented the radiators recently?

southcoastrgi

are the pipes in a plastered (solid) wall or a stud wall ?

daveyjp

Start with bleeding the radiators every week or so. If its anything like our system it took about 4 weeks for me to get to a point where there was no air in the system

keystone

Gremlins - clearly.

Cheers

Avoriaz

chris1012 wrote: »

They do lead to a radiator with a TRV.

The knocking went away again but tends to come on during the first bhr of the heating being on.

How is this related to the TRV?

Is the pipework copper or plastic? If copper, that suggests badly installed pipework as a possible cause.

Copper pipes expand and contract as they heat up and cool down and should be sleeved or protected with a cloth rag or in some other way when run through wooden joists etc so that the pipe can move smoothly. If it is wedged in a notch in a wooden joist for example without some sleeving, it can't move smoothly so it will move in tiny little jerks, making a knocking noise as it does.

That explains why the noise stops after an hour or so as the pipework has heated up and more or less stabilised. The noise may disappear or not be so pronounced on cooling down as it cools down far slower than it heats up.

I probably haven't described that very well but that is the general idea. It is a not uncommon problem that I have experienced myself.

Have you asked the plumber or installer to investigate?

It could be trapped air or some other cause.

Ectophile

My central heating has always made knocking noises when the pipes are heating up or cooling down. I've never worried about it.