Understanding room thermostats, saving on heating

[Harry Bloomfield]

I just find it hard to get round the idea of controlling the temperature of all rooms based on one room, in a house where I want the rooms at very different temperatures (not even throughout). I only want to heat the rooms I'm in/using.

You cannot turn the room off, where the thermostat is located, but you can turn the TRV's down in the unused rooms. Alternatively, if it's a wireless stat, you could carry it to which ever room you are in, and set the TRV in that room to maximum.

You should never turn TRV's completely off, otherwise in freezing conditions, there is the risk of pipework and radiators freezing.

I switched because I had very poor hot water flow upstairs.

I'm surprised you have more flow from a combi, than you had with stored HW - it suggests it was wrong plumbed, or you had a restriction somewhere.

 

[fixitflav]

I'm surprised you have more flow from a combi, than you had with stored HW - it suggests it was wrong plumbed, or you had a restriction somewhere.

Why a surprise? The flow depends on the mains pressure and the height of the CWST. Sounds like the CWST is on the low side and can't be raised, so more often than not mains would be better. But it should have checked to make sure the change is worthwhile.

 

[Millstone]

The old system had a clock that meant I could set the boiler to come off/on at certain times of day. It was only 24hr -not 7 day - that was a defect. But other than that I could simply switch the heating off. As well as controlling all rooms via valves on the radiators when it was on. So I either had the heating off completely, or heating on with all valves turned down except in rooms I was using.

 

[Harry Bloomfield]

Why a surprise? The flow depends on the mains pressure and the height of the CWST.

Because the flow from the combi, is limited by its ability to heat the water fast enough. My CWST, is mounted directly above the bath, floor mounted in the loft, fed with 22mm. I have an extremely good flow at the hot tap.

 

[fixitflav]

Because the flow from the combi, is limited by its ability to heat the water fast enough.

He didn't give the combi output, but they're usually around 30kW, enough to give reasonable HW flow, or what's the point? Unlikely that's the reason for the low flow.

My CWST, is mounted directly above the bath, floor mounted in the loft, fed with 22mm. I have an extremely good flow at the hot tap.

Same here!

 

[endecotp]

The old system had a clock that meant I could set the boiler to come off/on at certain times of day.

So do you now not have any way to have the heating automatically on/off at different times of day?

If so, that seems like a defect. It is common practice, on a modern system of this type, to have a time-clock (“programmer”), a room thermostat, and TRVs. Often the first two combined into a single box.

 

[ericmark]

I'm particularly struggling to understand the point of the room thermostat and why I can't just control heating/limit costs at the radiator in each room.

You can, Drayton Wiser has that option.

However, there are so many systems and options, there is no one correct answer, so the major change was the condensing boiler, these boilers unlike the previous types, needed the return water to be cool enough to extract the latent heat from the flue gases, so the whole system needed to change to suit the new boiler.

There was early on the Honeywell EvoHome

which allowed one to control the home room by room, but in the main, we did not have programmable TRV heads, so neither could we really have a programmable wall thermostat, they will simply not work together.

So there have been attempts to use non-programmable TRV heads, with a programmable wall thermostat, by not having a TRV in the same room as the wall thermostat. And there has been a lot of talk about when using TRV to do all the control, as to how the boiler works when only one is asking for heat.

Basic idea is, as the TRVs close the by-pass valve opens, sending hotter water back to the boiler which in turn causes the boiler to modulate (turn down) until it has modulated to its minium output at which point it uses a mark/space ratio turning the boiler off and on to further reduce output.

So with say this house with 14 radiators, as the first 7 slowly close great, but if the boiler can only modulate to 6 kW, and each radiator is 2 kW, then by time we reach the last area to reach the threshold, the boiler will be turning on/off all the time, so it seems to make sense to link some radiators or use some method so the boiler cycles less.

So it seems prudent not to have all linked TRV heads, but which are linked, and which are not, is not so easy to work out. I have my wife's bedroom linked, and no other bedrooms, they all have programmable TRV heads, but only hers is linked, so once her room is warm, the heating will turn off even if other rooms are cold. And the other bedrooms have the TRV heads set a little higher so to ensure we don't have only one room needing heat.

So heating systems are designed by heating and ventilation engineers who work out what is required, engineer means over level 3 trained, i.e. they went to University not just a tech collage. To have an engineer design the system cost money, I am only an electrical engineer, but I did expect to be paid more than someone with just a level 3, so often heating systems are not designed, they are just put in the same way as they have done for the last 50 years, and often not to the best design, this has resulted in many heat pump installs being very expensive to run, as the design has been simply this is how I have always done it, not working out what is needed for the home.

I live in a house designed with 5 bedrooms, but only 2 are used as bedrooms, and this is common, so the heating system needs to be flexable and able to use rooms as an office etc, which may not be on the ground floor, so two zones don't work, each room is its own zone.

 

[Millstone]

Thanks everyone for comments - I'm beginning to get my head round this.
For now my room thermostat is on a stand so I can put it in any room. My understanding is that if the room has a TRV and I turn the TRV up to the max/fully on, it won't "block" the room thermostat. If that's correct, could I have TRVs on all radiators and then choose in which room to put the room thermostat - always as long as I turn the radiator TRV in that room up to max?

 

[denso13]

For now my room thermostat is on a stand so I can put it in any room. My understanding is that if the room has a TRV and I turn the TRV up to the max/fully on, it won't "block" the room thermostat. If that's correct, could I have TRVs on all radiators and then choose in which room to put the room thermostat - always as long as I turn the radiator TRV in that room up to max?

Turning it up to max is a temporary solution really. They'll still interfere with one another if the max on the TRV is similar to the setting on the room stat.

Better to keep the room stat in what is normally the hottest room and remove the TRV in there.

Sounds like your sytem wasn't designed with the user in mind at all.

 

[Harry Bloomfield]

My understanding is that if the room has a TRV and I turn the TRV up to the max/fully on, it won't "block" the room thermostat.

Correct!

If that's correct, could I have TRVs on all radiators and then choose in which room to put the room thermostat - always as long as I turn the radiator TRV in that room up to max?

Also correct!

But, if all radiators are fitted with a TRV - always ensure one radiator, is set to maximum, unless your system has a bypass. This is to ensure that, should all the TRV's be closed at the same time, your boiler always has a means of pumping its heat somewhere, to get rid of it.

 

[Millstone]

ok. The boiler is a Worcester Bosch - Greenstar CDi Compact. I've just done a search of the online manual and there was no "find" for the word bypass. So maybe it doesn't have one of these?
So the issue then is that if I somehow forgot to put a TRV to max when I had the thermostat in the same room, it wouldn't just be a potential waste of gas, but actually dangerous or damaging to the boiler (boiler overheating)?

 

[denso13]

You have a brand new system, get the installer back and explain what you need. Workarounds will end up costing you money.

It isn't difficult.

 

[Harry Bloomfield]

So the issue then is that if I somehow forgot to put a TRV to max when I had the thermostat in the same room, it wouldn't just be a potential waste of gas, but actually dangerous or damaging to the boiler (boiler overheating)?

It shouldn't be dangerous, it simply wouldn't be good for the boiler. You might get a situation where the room stat is demanding heat, all the TRV's have been satisfied, and have closed, and so your boiler is heating water, with no where for it to go - it would be operating on it's overheat stat, and wasting gas, until a TRV opened, or the room stat switched off.

Modern boilers, directly control the pump, so they can run the pump for a while after the boiler stops burning, to draw the last of the heat from the boiler, for extra economy too.

A bypass, opens at a pre-set pressure, to allow some flow, to remove heat from the boiler.

 

[Millstone]

ok. I found this, about the boiler - presume this means there is no bypass included

 

[Harry Bloomfield]

ok. I found this, about the boiler - presume this means there is no bypass included View attachment 412026

Yes! Your best solution, might be to remove the TRV head in the bathroom, so it isn't accidentally closed.