Water hammer with Thermostat rad valves Potterton Profile60

[cortinaestate]

My house has 12 radiators, and I recently had thermostatic valves fitted to 10, and new valves throughout.
Since then, when the system gets up to temperature, I get an effect like water hammer from 2 bedroom rads. When you investigate, the vibration is in the thermostatic valves. Frequency is about 5 beats per second, so not as violent as water hammer.
The thermostatic valves are set to 4 (scale of 1-5). If I make a slight adjustment either side of the the currnet rad setting, that seems to close or open the valve sufficient to stop the noise. But it sometimes comes back later.
I have spent a lot of time bleeding air from the system, and don't think there is any significant amount of air left.
Does anyone know why this happens and how I can overcome it please?
(I have a conventional boiler & pump system for heating & hot water. System is over 30 years old; Boiler replaced about 8 years ago; Potterton Profile 60 boiler. System has been flushed by plumber.)

 

[HERTS P&D]

Are the TRV's bi-directional?

If not then they are fitted on the wrong end.

Andy

 

[doitall]

As above but most likely the differential pressure is too high.

If you have a by-pass valve open it a tad

 

[spraggo]

Turn the pump speed control down to 2 if still chattering turn down to 1.

 

[D_Hailsham]

Balance the system.

See How to balance a CH system

 

[Garygas69]

They are fitted the wrong way round

 

[doitall]

They are fitted the wrong way round

Or the pressure differential is to high.

If the valve was fitting the wrong end the knocking wouldn't stop when you adjust the valve

 

[gas112]

Bi directional valves can still be noisy especially cheap one . They should always be fitted on the flow.

 

[Garygas69]

They are fitted the wrong way round

Or the pressure differential is to high.

If the valve was fitting the wrong end the knocking wouldn't stop when you adjust the valve

how do you adjust the diff press with an automatic by-pass valve? Trust me they are the wrong way round.

 

[doitall]

They are fitted the wrong way round

Or the pressure differential is to high.

If the valve was fitting the wrong end the knocking wouldn't stop when you adjust the valve

how do you adjust the diff press with an automatic by-pass valve? Trust me they are the wrong way round.

Maybe, maybe not, it could be either.

 

[D_Hailsham]

how do you adjust the diff press with an automatic by-pass valve?

It's easy - think about it!

Trust me they are the wrong way round.

After only eight posts???

 

[doitall]

I think the OP's done a runner.

Need info if he's still looking.

 

[bell824]

I think the OP's done a runner.

Need info if he's still looking.

dia we both know we don't need info the installer has obviously not fitted the valves the correct way round onthe correct side of the radiator!!!!

 

[doitall]

I think the OP's done a runner.

Need info if he's still looking.

dia we both know we don't need info the installer has obviously not fitted the valves the correct way round onthe correct side of the radiator!!!!

We don't know nothing of the sort.

Most TRV's are bi-directional now, and in any case if they knock because they are on the return, they don't usually stop when you adjust the temperature setting.

Could still be either.

 

[Garygas69]

how do you adjust the diff press with an automatic by-pass valve?

It's easy - think about it!

Trust me they are the wrong way round.

After only eight posts???

After only eight posts ??????????????