TRV and wall thermostat in the same room, how can it work any other way?

[ericmark]

This is from Hive instructions for the SLT3 system. But it does not seem to make sense! If you don't have a TRV in a room, how do you stop the room overheating? Clearly, the TRV schedule needs to be the same as the wall thermostat, or slightly higher, but if my living room did not have TRVs then when my wife's bedroom TRV called for heat, or the hall wall thermostat called for heat, then the living room would overheat.

It just seems a daft statement to make, I can see how one would want to link thermostats in the same room, I know my cheap eQ-3 thermostats (TRV heads) can be linked when there are two radiators in the same room, and Energenie TRV heads were claimed to link to Nest wall thermostats, it did not work when tried, my Wiser TRV does not show ability to link, but would think it would need to be set to same room for that option to be shown?

I have three thermostats (two wall and one TRV head) all linked to the same motorised valve, which when opened will run the boiler, I can't see how one could remove the TRVs in any room with wall thermostats without that room overheating when other thermostat called for heat, am I going daft?

 

[Mister Banks]

The room thermostat controls the heat in the room and stops it overheating. If a manual TRV, or any TRV not controlled by the room thermostat, is also in the room then it may turn off the radiator before the thermostat gets to temperature, in which case the thermostat never switches the boiler off because it never reaches the set temperature.

 

[oilhead]

It all depends on the relative settings of the thermostats. Presumably the wall stat is a full system thermostat and controls the whole system whereas the TRV are specific to one room. Surely the normal set up would have a full system control in a relatively open area, with localised control for individual areas. If all of your three thermostats control the same motorised valve, then no wonder you spend hours bemoaning the shortcomings of your heating.
this must be the most discussed system on this forum and illustrates a situation of nothing to do and all oay to do it, which ihave encountered in a lot of my heating work experience.

 

[Harry Bloomfield]

This is from Hive instructions for the SLT3 system. But it does not seem to make sense! If you don't have a TRV in a room, how do you stop the room overheating? Clearly, the TRV schedule needs to be the same as the wall thermostat, or slightly higher, but if my living room did not have TRVs then when my wife's bedroom TRV called for heat, or the hall wall thermostat called for heat, then the living room would overheat.

It makes perfect sense to me Eric! The thermostat, is to turn the boiler on and off, at set temperatures. The TRV, is designed to limit the room temperature, they close at the temperature you set for the room.

If the thermostat is set to a higher value than the TRV, the boiler will never switch off. If the thermostat is set to a lower value than the TRV in the room, the room can never achieve it's set temperature. Therefore, you put the thermostat in a heated space, where the radiator has no TRV fitted, or set it to MAX, or remove the TRV head.

 

[fixitflav]

If you don't have a TRV in a room, how do you stop the room overheating?

The roomstat does it

 

[ericmark]

With a manual head on the TRV the difference between fully open and fully closes is massive, around 2ºC at least, it is also lower down to the wall thermostat, and further away from the source of heat.

the TRV at bottom and to one side of the radiator is in about the best location, monitoring the return air, where the wall thermostat is 50% closer to the air heated by the radiator due to thermals. Since I can monitor my TRV heads and wall thermostats from the PC I know when heating is running, the wall thermostat shows 0.5 to 2ºC higher than the TRV head. Hall now TRV 17ºC Nest on wall 21ºC, living room TRV 1 22ºC, TRV 2 20.5ºC Wiser on wall 24ºC. So if all set to same temperature, the Wall thermostat will always turn off before the TRVs.

What the TRV does is stop room overheating should another rooms' thermostat be calling for heat from the boiler.
Today there is a small not so much a problem, but a niggle, my wife's bedroom causes a 20 kW boiler to run, to heat a 3 kW radiator, I have considered an electric heater, which would use excess solar, however her room not tidy enough for it to be safe with an electric heater, so shelved that idea.

Yes, in a perfect world, every radiator has a linked TRV head, so its own thermostat able to turn on the boiler. The TRV is a thermostat, and they all will turn the boiler on and off, and if lucky enough to have a gas boiler, up and down, there are wall thermostats which can turn the boiler up/down, both mine could if I had a boiler OpenTherm enabled. But my oil boiler is simple on/off. But the comment

The TRV, is designed to limit the room temperature, they close at the temperature you set for the room.

is fundamentally wrong, the TRV is designed to control in an analogue way, but unless using a linked TRV head, it can't turn off the boiler fully, be it an on/off boiler or a modulating boiler, unless linked, the boiler would keep cycling on/off even on a warm day, as it would have no way to know the TRVs are all closed, until it tries pumping water around the system and the by-pass valve lifts sending hot water direct back to the boiler.

In my case, since C plan, it has to heat all the pipework from cylinder to boiler as well. So I would say the wall mounted room thermostat is designed to turn off the boiler on a hot day. On a cold day no need for a wall mounted room thermostat, I am careful to say wall mounted, as clearly the TRV is also a room thermostat. Clue is the T in TRV.

There is a balance, we could fit Wiser TRV heads in every room, and there would be no need for any wall thermostat. The reverse is not true, fitting wall thermostats in every room would not do away with the need for TRVs.

Both my pervious houses as built had no TRVs. The first one, however much we tried closing the bedroom hot air vents, bedrooms always too hot, next house used water rather than hot air, and the big problem was a bedroom door left open, if kept closed you could just about with lock shield valves throttle back bedrooms, but forget and leave a door open, and bedroom like a sauna, TRV heads upstairs cured this, downstairs was open plan, so one wall thermostat controlled all, and it was not until I returned to parents house, I even thought about central heating, mine worked, and if it works, why fix it.

Parent's house was first with a modulating boiler, new central heating fitted, by cowboys it seemed, the power shower was left running even though illegal with the combi boiler fitted, and I saw first hand how TRVs should work, but what transformed that house, was adding a TRV to hall radiator. I was told not to, and every book said don't have a TRV and wall thermostat in the same room, but doing so cured all the problems.

In a hall, believe it or not, one end we have a door to the outside. Open that door and take mother in or out in her wheelchair, and the hall is cold, set the lock shield high enough to reheat the hall in a reasonable time, and the wall thermostat turns off the heating to the rest of the house. Set the lock shield for when outside door not opened, rest of house gets warm, but as soon as front door opened, hall cools and stays cool for ages, and the boiler is cycling on/off as using less than minium output.

Add a TRV to the hall radiator, set to start to close at 17ºC and set the wall thermostat to 19ºC and the hall heats up fast 15ºC to 17ºC at which point the TRV starts to close, so it takes quite a long time to get from 17ºC to 19ºC allowing rest of house time to also heat up. It transformed the house heating.

OK, will admit there is a problem with some TRV heads, being marked *123456 is not helpful, I can see why, set to around 2.5 it will start closing at around 17ºC and not be fully closed until 21ºC, so only way was fit an electronic head, once the lock shield set, it could have the mechanical one refitted, and it adjusted so room correct temperature, but until lock shield set, no idea which to adjust.

However, the quote was from Hive, where the TRV head is linked to the boiler running, not sure if same as Wiser and a wall thermostat can be done away with, but they are linked, so the statement makes no sense.

 

[Harry Bloomfield]

With a manual head on the TRV the difference between fully open and fully closes is massive, around 2ºC at least,

I think you are over thinking it. It doesn't matter, they gradually close, at a predictable temperature, which means they do precisely control the room temperature. Basically, they will ramp up and down the flow through the radiator, to match the setting - what more do you want? The only thing a TRV cannot do, it demand heat from the boiler.

 

[Mister Banks]

With a manual head on the TRV the difference between fully open and fully closes is massive, around 2ºC at least, it is also lower down to the wall thermostat, and further away from the source of heat. View attachment 378251 the TRV at bottom and to one side of the radiator is in about the best location, monitoring the return air, where the wall thermostat is 50% closer to the air heated by the radiator due to thermals. Since I can monitor my TRV heads and wall thermostats from the PC I know when heating is running, the wall thermostat shows 0.5 to 2ºC higher than the TRV head. Hall now TRV 17ºC Nest on wall 21ºC, living room TRV 1 22ºC, TRV 2 20.5ºC Wiser on wall 24ºC. So if all set to same temperature, the Wall thermostat will always turn off before the TRVs.

What the TRV does is stop room overheating should another rooms' thermostat be calling for heat from the boiler.
Today there is a small not so much a problem, but a niggle, my wife's bedroom causes a 20 kW boiler to run, to heat a 3 kW radiator, I have considered an electric heater, which would use excess solar, however her room not tidy enough for it to be safe with an electric heater, so shelved that idea.

Yes, in a perfect world, every radiator has a linked TRV head, so its own thermostat able to turn on the boiler. The TRV is a thermostat, and they all will turn the boiler on and off, and if lucky enough to have a gas boiler, up and down, there are wall thermostats which can turn the boiler up/down, both mine could if I had a boiler OpenTherm enabled. But my oil boiler is simple on/off. But the comment

is fundamentally wrong, the TRV is designed to control in an analogue way, but unless using a linked TRV head, it can't turn off the boiler fully, be it an on/off boiler or a modulating boiler, unless linked, the boiler would keep cycling on/off even on a warm day, as it would have no way to know the TRVs are all closed, until it tries pumping water around the system and the by-pass valve lifts sending hot water direct back to the boiler.

In my case, since C plan, it has to heat all the pipework from cylinder to boiler as well. So I would say the wall mounted room thermostat is designed to turn off the boiler on a hot day. On a cold day no need for a wall mounted room thermostat, I am careful to say wall mounted, as clearly the TRV is also a room thermostat. Clue is the T in TRV.

There is a balance, we could fit Wiser TRV heads in every room, and there would be no need for any wall thermostat. The reverse is not true, fitting wall thermostats in every room would not do away with the need for TRVs.

Both my pervious houses as built had no TRVs. The first one, however much we tried closing the bedroom hot air vents, bedrooms always too hot, next house used water rather than hot air, and the big problem was a bedroom door left open, if kept closed you could just about with lock shield valves throttle back bedrooms, but forget and leave a door open, and bedroom like a sauna, TRV heads upstairs cured this, downstairs was open plan, so one wall thermostat controlled all, and it was not until I returned to parents house, I even thought about central heating, mine worked, and if it works, why fix it.

Parent's house was first with a modulating boiler, new central heating fitted, by cowboys it seemed, the power shower was left running even though illegal with the combi boiler fitted, and I saw first hand how TRVs should work, but what transformed that house, was adding a TRV to hall radiator. I was told not to, and every book said don't have a TRV and wall thermostat in the same room, but doing so cured all the problems.

In a hall, believe it or not, one end we have a door to the outside. Open that door and take mother in or out in her wheelchair, and the hall is cold, set the lock shield high enough to reheat the hall in a reasonable time, and the wall thermostat turns off the heating to the rest of the house. Set the lock shield for when outside door not opened, rest of house gets warm, but as soon as front door opened, hall cools and stays cool for ages, and the boiler is cycling on/off as using less than minium output.

Add a TRV to the hall radiator, set to start to close at 17ºC and set the wall thermostat to 19ºC and the hall heats up fast 15ºC to 17ºC at which point the TRV starts to close, so it takes quite a long time to get from 17ºC to 19ºC allowing rest of house time to also heat up. It transformed the house heating.

OK, will admit there is a problem with some TRV heads, being marked *123456 is not helpful, I can see why, set to around 2.5 it will start closing at around 17ºC and not be fully closed until 21ºC, so only way was fit an electronic head, once the lock shield set, it could have the mechanical one refitted, and it adjusted so room correct temperature, but until lock shield set, no idea which to adjust.

However, the quote was from Hive, where the TRV head is linked to the boiler running, not sure if same as Wiser and a wall thermostat can be done away with, but they are linked, so the statement makes no sense.

You are getting manual TRV’s and so called “smart” TRV’s mixed up. A manual TRV will not shutdown the boiler and is a temperature limiter, a so called smart TRV if connected to a device that connects to a boiler does have the capability to shutdown the boiler. This is why you never have a manual TRV and a room thermostat in the same location. The Hive statement must be referring to manual TRV’s.

 

[ericmark]

The Hive statement must be referring to manual TRV’s.

You are seeing my point, I have in this house a number of types of TRV heads, the flat under main house only 4 rooms, mechanical TRV heads, as hardly used, the main house 3 x Energenie electronic internet connected, 5 x eQ-3 electronic bluetooth only, 1 x Kasa electronic internet connected, and 1 x Wiser electronic internet connected and connects to the boiler hub.

The electronic have a droop of around 1ºC +/- 0.5ºC, where the manual have around a 4ºC droop. But the main thing is the electronic are set in ºC where the mechanical it is guess work, and the electronic are programmable, and the mechanical is not. So with electronic bedrooms are not heated in the day, and living rooms not heated when we are in bed.