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Our central heating system is just over 1 year old.
When the heating has been on for some time the radiator valves make a hissing noise (like water coming to the boil in a kettle.) If I turn down the TRV the noise stops but appears again if I turn them back up.

How can I fix this? It happens on several TRV's but not all.
Thanks in advance
Kevin :? :?

Is the boiler stat turned up too high? Is the boiler itself kettling or just the TRVs making funny noises?

Turning the TRV down just closes the valve. Each TRV should have an arrow on the body indicating the recommended direction of flow. Are they fitted the wrong way round? Modern good quality TRVs such as Danfoss, Pegler, Honeywell etc are bi-directional and quiet. If yours are a cheap and cheerful make then they may not be bi-directional or quiet.

Is it a combi boiler? If so what is the pressure reading on the gauge? If its more than iro 1.5 bar when the system is hot then you need to let some water out to reduce the pressure.

Did your installer fit an autobypass valve?

Cheers

Thanks for the reply.
The radiator dial on boiler is set to max. It's just the trv's hissing prior to them shutting off when the required room temp is reached, the boiler itself is very quiet.
My trv's are Pegler bulldog and are bi-directional I think (two arrows on the stem?) The Boiler is a Worcester Bosch 30cdi. The pressure gauge reads 1 bar when not operating and aroung 1.5 bar when the system is running.
I have replaced the head on the noisiest one with a Drayton trv, seems much quieter.

Any further ideas?
Thanks
Kevin

Thanks for the reply.
The radiator dial on boiler is set to max. It's just the trv's hissing prior to them shutting off when the required room temp is reached, the boiler itself is very quiet.
My trv's are Pegler bulldog and are bi-directional I think (two arrows on the stem?) The Boiler is a Worcester Bosch 30cdi. The pressure gauge reads 1 bar when not operating and aroung 1.5 bar when the system is running.
I have replaced the head on the noisiest one with a Drayton trv, seems much quieter. I have no idea if the installer fitted an auto bypass valve (where would it be?)

Any further ideas?
Thanks
Kevin

OK thanks for reply which helps.

Where is the roomstat fitted? I'm guess in the hall - thats normal. In that case the rad in the hall will (or should) NOT be fitted with a TRV. There are two reasons for this:

1. The rad acts as a crude bypass.

2. The TRV would close when the room reaches the required temp by the TRV. But if the roomstat is set to a higher temp then it will continue to call for heat but it will never get hotter because the TRV is keeping the temp down. So all you do is burn gas for no effect.

When he did the install he should have balanced the system. Take note of the exact number of turns (to the nearest 1/4 turn) that the lock shield valve is set tp from its current position to fully open. With both valves fully open does the noise stop?

An autobypass valve looks like this:

http://www.awin1.com/awclick.php?mid=12 ... l&ts=93012

BUT your boiler may have got an inbuilt bypass. Data should be in the Manufacturers Instructions and the installer should have adjusted it for the best setup.

Just noticed that you said the installation is only a year old - sorry should have spotted that. In that case I think you should give your installer a call as its likely that the remedy lies in his hands.

Cheers