Central heating radiators

  JYPX 19:51 29 Nov 2010

It is sheer coincidence that I am asking this today...ha ha. All my radiators have an individual thermostatic valve - except one. This radiator, in a bedroom, is allways too hot and so is constantly being turned on and off with the control valve. The heating engineer told me that TRV's can be fitted to all except one radiator but I can't recall what the reason was. Does anyone know why this is? I think my current set-up is wasting money.

  NORFOLK SPARKY 19:58 29 Nov 2010

The reason is that one radiator should be controlled by a room stat so when that is satisfied the boiler shuts down completely. on the systems I have been invlved in this has usually been in the hall. if you have trv's on all the radiators and no room stat the boiler keeps on working when it gets cold on it's stat it fires the boiler even if no room needs heat. this is considered by the powers that be to be ineficiant.

One radiator is left unregulated to dissipate any extra heat as a control measure.

  JYPX 20:31 29 Nov 2010

Thank you. The room stat is in the hall so I guess I need to nominate the hall radiator to be the one without the TRV. I am still struggling to see how this will work - the hall will get "too hot" and the wall stat will then shut down all the heating regardless of the individual TRV's! (I think)
If I make this change would it then be unsafe to turn off the hall radiator at some times (leave the wall stat on a fairly high setting and let the TRV's do the job) or just not the normal practice?

  alB 21:41 29 Nov 2010

On our system I set the hall stat to 20 degrees and then adjust each room on the individual radstat to a comfortable temperature, in the larger rooms/bedroom usually near maximum but in the smaller bedroom and kitchen etc only just over half, with a bit of tweaking the whole house is more or less the same temperature all over, and once set it doesn't need adjusting much except to turn the wall stat up a couple of degrees when the weather gets really cold...like now !! ...alB

  carver 21:43 29 Nov 2010

I was told the reason you have one rad uncontrolled (straight through) is in the event that all the thermostatic controlled rads should shut off and the boiler continues to work you have in effect a safety valve in that rad, it should be the one nearest boiler or hallway.

Otherwise you have very hot water in the heat exchanger with no were for it to go which could result in damage to the boiler.

  hssutton 22:05 29 Nov 2010

A boiler has it's own thermostat, so a room stat although desirable it's not essential.

On combi boilers a specified minimum amount of water must pass through the heat exchanger. even when all rads close down (this amount could vary depending on boiler make/size used). This is usually achieved by the fitting of a by-pass. It's normal for a 15mm pipe with control valve to be fitted between the flow and return. In this situation all rads could have TRVs.

  Forum Editor 23:30 29 Nov 2010

have an automatic bypass built in and in that situation it's not necessary to leave a radiator without a TRV.

  onionskin 23:59 29 Nov 2010

I leave the bathroom radiator fully open, just in case. No harm in having a nice warm bathroom.

  PalaeoBill 01:08 30 Nov 2010

On my system, when the room stat clicks off, a motorized valve closes cutting all but one of the radiators off from the boiler.
The boiler has an automatic bypass, but it is only a short length of pipe, too short to dissipate the heat from the heat exchanger. For this reason the plumber left one radiator (the bathroom one) permanently connected to the boiler. This doesn't have a TVR. All of the other radiators do.
To my cost I discovered what happens if you close down the control valve on that bathroom radiator to try and make it less hot. Hot water just cycles around the bypass, it has nowhere to go and doesn't cool down for ages. The boiler has a pump overrun facility so it runs the pump continuously to try and remove heat. The pump starts to make a racket and eventually burns out. Then the heat exchanger warps.

  PalaeoBill 01:09 30 Nov 2010

or even TRV

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