One radiator in CH system does not work

[dchopp]

Please can anybody help me with this problem. The problem is that the radiator in the downstairs cloakroom will not work. I have taken the radiator off the wall and checked the valves etc.

The pipework to the radiator comes down from the upstairs bedroom. The pipes tee off close to the bedroom radiator which works normally but the pipes never get warm

I have carried out a few tests to no avail. With the CH warmed up I have opened the drain cock and bleed valve with either valve closed and hot water comes down the pipes to the radiator.

I have run the pump and with all other radiators closed hot water does not enter the pipework

If anybody has suggestions to resolve this they would be greatly appreciated. Thank you.

 

[seco services]

has it ever worked ?

 

[doitall]

Have you teed off both pipes or just one.

 

[dchopp]

Thank you Karl and doitall.

The radiator is teed off two separate pipe runs below the bedroom radiator but I don't know whether it has ever worked as we only purchased the house 2 years ago and it has not worked in that time.

 

[seco services]

you say you can get hot water down both pipes.
did you flush the rad out when off ?
and the bedroom rad gets hot ?

 

[Nige F]

what size are the pipes

 

[dchopp]

Thank you Nige. The pipes are all 1/2 inch.

Karl. Thanks for your further interest. I confirm the bedroom radiator gets hot and I can get hot water down both pipes by undoing the valve nuts, drain cock and bleed valve. I have taken the radiator off a number of times and there is nothing to prevent water flowing through. I have examined the valves and they open and close when screwed. This is why I am completely mystified.

David

 

[MANDATE]

sounds to me that the route of the water going down to a radiator and up again is offering more resistance, compared to continuing along the flow.
Water will avoid the hardest route if it can.
Two things come to mind. Does the system need balancing to ensure the problem radiator gets its share of the available water.
Also is there a by-pass valve (open too much) allowing a easier route for water to return to boiler as against being forced around the CH circuit.

 

[dchopp]

Mandate- your reply prompted me to look at the equipment. There is no by-pass valve as I have a 3 port diverter valve. I checked out the pump and changed a head setting and subsequently found the radiator had warmed up. Wonderful.

Thanks for your advice

 

[vinnychase]

Has it got a Thermostatic Radiator Valave??

 

[seco services]

Has it got a Thermostatic Radiator Valave??

I have taken the radiator off the wall and checked the valves etc.

 

[rebelbuttmunch]

Mandate- your reply prompted me to look at the equipment. There is no by-pass valve as I have a 3 port diverter valve. I checked out the pump and changed a head setting and subsequently found the radiator had warmed up. Wonderful.

Thanks for your advice

Whats a head setting ? Is it pump speed?

 

[MANDATE]

Glad to hear you've had some success. But to me it indicates the system is was not balanced after the radiator was fitted.

 

[dchopp]

Thank you again for your responses.

The radiator does not have a thermostatic valve and alhough I have had some success the radiator took some time to warm up this morning. I appreciate the system requires balancing and there is flow resistance as during the whole saga I have shut down all the other radiators to try and get this one to work.

I feel that there may have been a build up of sediment in this radiator which was cleared by the emptying of the system as I changed the pump as it rattled and had checked the setting of the pump last winter and had turned the selector switch to various settings. With regard to the "head setting" I have taken this wording from the Grundfos Alpha+ pump instructions. There are six settings on the selector switch, three are for constant-load and three for variable-load both for high to low resistance. I presume this is to do with the speed of the pump. As stated earlier I am a novice on this.

My recent success was obtained when I turned the selector switch from large constant-load setting to variable-load setting. This cleared any thoughts about sediment or air causing the radiator not to work. Out of interest I did turn back the selector switch to variable-load but the hot water stopped coming to the radiator.

I have yet to discover what happens when I open up further radiators on the CH system.

Thank you once again for your interest and assistance

David

 

[MANDATE]

I reckon when you open up other radaitors, your problem will return.
The water will take the path of least resistance.
Each radiator has two valves, one being to turn the radiator on or off (unless it's a thermostatic one) and the second valve called a 'lockshield valve'. The lockshield is set somewhere say between 1/2 open and 1/4 open for example. This partial opening restricts the flow of water into the radiator. If you closed all the lockshields by 1/4 turn, ( with the problem rad lockshield fully open) this would create more resistance and you could expect this to have some effect on your problem radiator. This may not fully cure your problem straight away, so you may have to make further adjustments of the valves, until there is no path of least resistance.
The by-pass valve likewise is adjustable to control the flow to the whole system. If its open too much the water may prefer to go back to boiler rather than go round the CH circuit.