Danfoss thermostatic radiator valve. Clunking/Knocking Noise

sicnarf · 13 Apr 2007

Hi,
I have a Vokera Combi Boiler and five radiators fitted with Danfoss thermostatic valves.

The thermostatic valves start making a repetitive knocking sound, I think this happens when they reach their set temperature and they're trying to shut down the flow to the radiator

The only way I've found to stop it is to put them on full so only the boiler controls the temperature, or to remove the thermostat from the valve.

I was told that the valves may have been fitted in the wrong direction against the flow of the water, but according to the one-way arrow on the valve and based on which side of the valve gets hot first, I believe they're fitted correctly.

Any suggestions what might be the problem, should I get a different kind of valve or thermostat ?

gas4you · 13 Apr 2007

Usually this is a sign that the water flow is the wrong way. At worst can sound like a pneumatic drill going

You could change them for the new cheap Danfoss RAS c trv which is adjustable for flow direction by you by twisting the internal adjuster.

sicnarf · 16 Apr 2007

gas4you,
Thanks for your reply. So I guess this means replacing the brass part of the valve, and having to shut off the radiators, and drain them etc?

I haven't disconnected a radiator before, so I'll have a look through this forum first to see if someone's posted a "how-to" for this.

Cheers.

pannierstan · 16 Apr 2007

You dont HAVE to buy new if you dont want to. Just make a note of which pipe gets hot first on each rad then remove the valve and fit it with the direction arrow going the right way.
It just means that the orientation of the valve might be vertical as opposed to horizontal.

Stan

doitall · 16 Apr 2007

Nothing to do with the radiator valve as such

The problem is pump head, turn the speed down and it may go away.

Failing that you will have to install an Auto by-pass valve in the system pipework.

pannierstan · 16 Apr 2007

doitall said:
Nothing to do with the radiator valve as such

The problem is pump head, turn the speed down and it may go away.

Failing that you will have to install an Auto by-pass valve in the system pipework.

Gasguru · 16 Apr 2007

Don't turn down the pump speed since most combi's require the pump to be on maximum setting either for hot water or pump overrun (dependent on design).

Make sure you havn't got TRV's on all the rads - at least one of your radiators should be fixed open without a TRV and that room controlled by a room thermostat .

Consider fitting an automatic bypass valve (this is often in addition to the boilers own bypass if it has one).

doitall · 17 Apr 2007

pannierstan said:
doitall said:

Nothing to do with the radiator valve as such

The problem is pump head, turn the speed down and it may go away.

Failing that you will have to install an Auto by-pass valve in the system pipework.

Click to expand...

Its the valve thats making the noise pannierstan, Its is the pressure differential which should not exceed 0.45bar (45kPa) which is causing the problem

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Danfoss thermostatic radiator valve. Clunking/Knocking Noise

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