If I put TRV valves on all the radiators will this cause problems? The problem I foresee is if all the radiator valves close, but the main thermostat doesn't turn off, in which case the pump will be working against closed valves and there will be no circulation through the boiler. Am I worrying about nothing or is this an issue? Thanks Simon
you do right to worry, the system should have a by pass, even when the boiler stat shuts off ,the pump will carry on for a few minutes to disapate the heat, and like you say if the rads are all shut, the pump will hydrolock,
Thermostatic valves do not close completely, they just close down enough to reduce the flow through the rad. They are more like a car accelerator than a switch. Yes. you will get an increase in the system pressure as the TRVs close down, but this is normally taken care of by having an Automatic Bypass Valve (ABV). The main problem of just relying on the boiler thermostat to turn the boiler on/off is that the boiler will continue to run long after the rooms have reached temperature. This wastes gas and costs you money. The correct way to do it is to have a room thermostat on the wall (living room or hall) and no TRV on the rad in that area. Provided the system is properly balanced the room stat will keep the boiler running until all the other rooms are up to temperature, it will then turn the boiler off. It's not a good idea to have the room stat in a warm room (e.g south facing) as that room will get up to temperature before the other rooms, so they will never get up to temperature.
Thanks for your answers. As we are in the process of gutting the house at the moment, some tinkering with the CH is 'quite easy'. So in an ideal world I guess I would ditch the TRV's and split the system into zones, as long as each zone has at least one open raditator then everythings OK? I guess with zone valves, the pump and boiler would shut off as soon as the last valve starts closing? And as a belt and braces measure, if I fitted a ABV then this would prevent damage if anyone closed off all the radaiators within a zone?
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