Understanding room thermostats, saving on heating

[Millstone]

I'm quite new to gas heating (grew up off grid) and trying to understand a combi-boiler gas central heating system, just installed to replace a simpler, gravity-fed system. It's been a shock to the system (old stone house and mine) with two radiators already burst due to higher pressure.

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. My own system had a "clock" dial type system linked to the boiler with times on it - and I could turn the boiler itself off/on at ignition.

My main aim has been to minimise spending on heating. I switch it on in winter as late as possible - usually mid-November - and off as soon as I can. Some winters I've more or less got by without. So I'm not looking for a house which is "heated to 18 degrees" etc. - didn't grow up with that and would actually find it uncomfortable! I'm used to indoor temperatures around 12-15.

In addition to that, my house has a back extension that I use very little and therefore only heat a tiny amount - basically to prevent pipes freezing/mould. I live in 2-3 rooms at the front.

Now I have this new boiler with TRVs on radiators. They've left the hallway radiator without a TRV and that's where they suggested I put the room thermostat. The hallway is central in the house but it's in a cold area that I never bothered to heat much in winter - I don't spend time there, and it's leaky due to windows - so I keep doors to it shut and heat other rooms.

My understanding of the logic behind the location that the hallway is a kind of central, average place in people's houses and so once the house "as a whole reaches" the temperature on the room thermostat, the boiler will cut out.

At any rate, I don't want the house "as a whole" heating that much. With no TRV on the hall radiator, it now has to keep on full blast until it reaches the temperature on the room thermostat. But if I set that really low - because I don't need to heat that area - it will then cut off heat to radiators I do want on in the rooms I'm using, surely?

Alternatively, if I set that hall room thermostat higher, to avoid it cutting off heat to rooms I do use, I'm having to heat the hall radiator due to lack of TRV on it.

Would it not be better to have a room thermostat in a room I want to heat?

Again, I understand that if you have a TRV in a room with a room thermostat, the two systems would compete. But if they are set to the same, desired, temperature for that room, I can't see that it matters.

Can anyone explain this clearly for a newcomer to gas?

 

[denso13]

Would it not be better to have a room thermostat in a room I want to heat?

You can have it in any room you like, just remove the TRV head in that room.

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.

Because the TRV's don't control the boiler and won't switch it off. The room stat will, when the set temperature is reached.

 

[Millstone]

Thanks! So in a room with a TRV, does it make any difference to how much gas I'm using if I turn the TRV down?
My instinct is to turn down radiators in rooms I'm not using, to save gas. But perhaps with this new system I will spend the same on gas whether I heat all these rooms or not? It seems a bit odd.

 

[denso13]

So in a room with a TRV, does it make any difference to how much gas I'm using if I turn the TRV down?

You'll use less if they are cooler. In reality, it might not make a huge difference.

 

[Millstone]

So have I made a mistake installing this new system? It feels like I now have to heat my entire house - extension included... I'm used to having heating "off" most of the time.

 

[denso13]

Turn down the TRVs in the rooms you want to be cooler and save gas? How was it controlled before, the combi and older "non combi" systems are essentially the same on the heating side.

 

[CountryFan]

A trv and room stat in the same room can give poor results, so place the thermostat in the cooler part of the house, eg where it's been mentioned about the hallway and set to the desired temperature, so maybe 15 degrees. Then set the trvs to the temperature you want to feel comfortable at and then just trial and error with it.

The reason for fitting a thermostat is to provide boiler interlock to prevent wasted energy.

 

[Millstone]

So if I place the room stat in the hallway, for example, and set it to about 12 degrees - I wouldn't want it more than that. The radiator there will come on and stay on until it reaches 12 degrees and then turn the boiler off - is that right?

Suppose I have another room that I'm actually in and want to heat it significantly warmer. Presumably it would stop heating when the hallway reaches its 12 degrees because the boiler has cut out?

And if I had the hall-room thermostat set higher, to avoid this, I have heat blazing out of it that I don't need?

 

[denso13]

And if I had the hall-room thermostat set higher, to avoid this, I have heat blazing out of it that I don't need?

Yes, that's how it works. Did the installer ask or did you say at all, that you always want the hall cool? It could have been sorted at the time by putting the room stat elsewhere, and still can be.

 

[CountryFan]

So if I place the room stat in the hallway, for example, and set it to about 12 degrees - I wouldn't want it more than that. The radiator there will come on and stay on until it reaches 12 degrees and then turn the boiler off - is that right?

No it's the temperature of the room that reaches 12 degrees, the radiator temperature is different so it can reach that target.

Suppose I have another room that I'm actually in and want to heat it significantly warmer. Presumably it would stop heating when the hallway reaches its 12 degrees because the boiler has cut out?

Yes, but you could then set the trv to maximum or one below this. Once the trv temperature has been reached then it will stop producing heat output to that radiator

And if I had the hall-room thermostat set higher, to avoid this, I have heat blazing out of it that I don't need?

Yes, sort of. Let's say you did set it at 12, the room might not take that long to achieve this temperature, but the trv would, but once the room temperature of the thermostat is reached, then this will stop the boiler firing and would only kick back in when the temperature drops until the demand is cancelled

 

[Harry Bloomfield]

Thanks! So in a room with a TRV, does it make any difference to how much gas I'm using if I turn the TRV down?

It certainly will.

My instinct is to turn down radiators in rooms I'm not using, to save gas. But perhaps with this new system I will spend the same on gas whether I heat all these rooms or not? It seems a bit odd.

Don't turn the radiators down, turn the TRV down - that is its purpose.

TRV's are designed to limit the temperature in a room/set the maximum temperature. The time controller sets when CH is available. The wall thermostat decides whether any heating is needed, so is essential to save you money on gas. The stat cannot do that, unless it is located in an heated area, where a radiator is located, not fitted with a TRV - otherwise, the two would be fighting. Depending on how you want the system to work, the stat should also not be fitted in a space, with an alternative source of heat, like a gas fire, because use of the fire, would cause the entire CH system to shut down.

A further point is, you do not have to set the stat, to a typical temperature you would want for an occupied room. My (wireless) stat, generally resides in the hall, and the hall radiator has no TRV fitted. It is programmed to a during the day temperature of 18C, 14C during the night. Close the living room door, and the room temperature will be higher, limited by the TRV, rather than the stat - but we often light the living room fire, which causes the TRV to close. The heating, when set back to 14C during the night, might come on just once per year, if we happen to have a really cold night.

It all works well, and is fairly economical on gas usage.

 

[fixitflav]

Suppose I have another room that I'm actually in and want to heat it significantly warmer. Presumably it would stop heating when the hallway reaches its 12 degrees because the boiler has cut out?

That's right, the solution is to throttle the hall rad more, so the roomstat there is less likely to be satisfied. The problem I see is when the outdoor weather is about 12° the roomstat will always be satisfied, so unless you turn it up you can't heat other rooms. Putting the roomstat somewhere else would be better.

 

[fixitflav]

So have I made a mistake installing this new system?

What made you change to a combi? There are pros and cons with a combi (mainly cons IMO), one problem being changing a gravity system to pressurised, as you've found. The installer should have pointed that out.

 

[Millstone]

I switched because I had very poor hot water flow upstairs. Before taking the plunge I had consulted many, many heating/plumbing engineers and basically this was the recommended fix - there was no room to raise my tank higher in the loft.
The only alternative would have been to have some sort of pump fitted to the cylinder but when I looked into that it was as expensive if not more.
So I went with this new system thinking it would be more efficient (because more modern) and solve the hot water flow. And to be fair, the hot water flow is a bit better.
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.

 

[denso13]

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

Although I'm not a fan you can fit smart TRVs in all rooms and have no room stat. You can then do whatever you want by controlling each room individually. Not how I'd go about it though.

How did you control your old system? I've already said the combi is no different, heating wise.