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In a normal house maybe. But not so sure in this particular one, especially during the warm up phase. The 2ft thick walls downstairs will still be emitting coolth, long after the modern upstairs bedroom has warmed up.

@Nickfromwales's suggestion of just wiring in an external wireless one is the easy solution to that. TBH I think that's likely the better option in anycase. But doesn't seem like something that will be ready for Monday.

The important thing is the thermostat is moved into the cold, old, part of the building, not close a raditor or other heat source. It doesn't strictly have to be the coldest room as long as its generally cold in the area. Putting it in the hallway or the bottom of the stairs is common. If you moved it into your warm bedroom/warm workshop that would be bad and might make things worse.

@zoothorn I think I was the one who saw you saying you were still cold and suggested you try again at making changes to things so you could get warm. I know you didn't come back here asking for that, but since you have a new system it does seem worth trying. I agree with @Nickfromwales that this thread could do with a timeout until after the engineer visit. We are all trying to help. I know some of the suggestions seem wrong to you. The go against your experience. All I can say is that people aren't making these things up, they are the result of real-life experience in their own and friends homes. We are passing on what has worked for us and many others. Once the engineer has visited then you have a choice, you can come back here and work with us to try new things (even things that seem wrong to you) to see if it works, or you can not. As a group I think we all think its possible for you to be much more comfortable than you are now (not perfect, but better). To be clear though, it will cost you more in bills. If you can't stand any higher bills (at least double what you pay now) then that puts a blocker on things.

Setback is the minimum temp you want the house to be kept at, ie, overnight if you are running a timer schedule. Rad temperature. 46C is lower than I was guessing based on your description of the rads being hot. Your system should be relatively efficient with rad temp of 46C. So a COP of >4 rather than the 2.5-3 I'd previously guessed. This is good. Though rad temperature and setback temperature are two different things so maybe he was talking about multiple things and the two got jumbled? Different to HW temp. Ideally HW temp should be a bit hotter. 55C maybe 46C is a fine temperature for your situation, I wouldn't worry about changing it but if you want to then ask the engineer on Monday.

The £700 is an approximate maximum amount of energy your heatpump could use in 1 month if running flat out 24x7. It is not what you need to spend to warm your house. That your bills are so low is a sign that your heatpump has been working much below it's maximum capacity and with some changes could provide much more heat. @Big Jimbo's question is a good one. Would appreciate your thoughts on that.

Couple of things to add: 1. The only time a 9kw heatpump would need to work flat out continuously in zoots property is during the few super cold days of the year, if that. The rest of the time it would work a lot less. 2. The electricity bill is averaged over the year, so even if you spend £600 in the worst month, the amount you pay monthly will be a lot less than that. 3. @S2D2's calcs assume a COP of 3. That's the measure of efficiency of the install. A COP of 3 is a good guess for zoot's current setup (maybe less) but with some changes the COP of 4.5 or even higher is possible. If that was done the amount of electricity used to produce the heat goes down a lot. Instead of needing 3kw of electricity it needs 2kw. So £446 running flat out vs £669.

As you said yourself the rads were coming on and off. They weren't on continuously. We have talked about how the thermostat is in the wrong place. The system may have been set to run, but the thermostat was stopping it running most of the time. Your bill would have been very much higher had it been actually producing heat constantly. Both @Dillsue and I have done some rough calcs for your place. The results are that your heatpump is likely not able to maintain 20C internally during the coldest days of the year. No company would want to install something that can't maintain 20C during the coldest days. In fact I suspect that most companies would want to make sure the heatpump could maintain 23C. That doesn't mean that the heatpump flat out wont work. Just that for 2-3weeks a year it will be colder than 20C inside. Given right now you are much colder than that I'm suggesting changes that could allow you to be warmer than you are now. @Big Jimbo is right though, if you want to be warm in your house you will have to be able to afford bigger bills. How much bigger is unclear, but his estimate of £250 is a good starting point. Some things are not as obvious as they seem. Because the old rooms have very thick walls, once they are cold they are difficult to warm up. So if you really want to prove your theory you need to run the house for at least a week, probably more with the heating on and rads warm continuously. If after 2 weeks of doing that, it's still cold then you will have proved your point (at as the house is now). If it's warmer but not toasty then we can have a conversation about making it better. Edit to add: if after two weeks of constant heating it's still deathly cold then its still not game over, just that improvements need to be made to the place and I'm not talking insulation. It's more likely plasterboard tent type issues or drafts (despite your best efforts).

The physics is the same, to get a comfortable house you will undoubtably have to spend more on bills than I do but the same principles apply. My mums house does not and she is able to heat that perfectly fine. Yes it costs her approx £2000 a year but its not cold (so long as the heating is on) Medium warm rads on 24x7 will output much more heat than hot rads on for short periods of time. 12 rads designed for heatpump temps should be able to output the full capacity of your heatpump without issue. The fact your energy bill is only £70 shows that this hasn't been tried yet. For you to get a warm house it will cost substantially more than £70 per month. If my mums leaky, mostly uninsulated house can be kept warm then so can yours. Take @Nickfromwales up on his offer. TRY to run your house in a different way. Physics and experience from people on this forum says it's possible. Unfortunately you've had a bad experience with previous installers putting a system in that wasn't set up right and gave the impression that your house is unfixable. Try to set that experience aside and start with a blank sheet of paper.

I'm saying the rads should be hot whenever the room is colder than your set temperature, including overnight. This is how I run my system, how @Nickfromwales runs his, ditto @JohnMo@marshian and many many more. With a TRV you can set the temperature in your bedroom lower, but the heat is required in the rest of the house to prevent the stone walls getting cold. Once they are cold then warming them up again is super difficult. Once your house is warm, the radiators will only be on as needed to maintain the warmth, but to get the house warm they need to be on continously, likely for many many days because your house is so cold right now. As I said many posts ago, I've found running my system 24x7 seems to be using less energy than running my system on a timer. The reason is that it takes a lot more energy to heat a cold space up than it does to maintain a constant temperature.

Maybe this helps: The Thermostat/controller is there to put heat into the system whenever the coldest room needs heat (to do this it needs to be located in the coldest room) The TRVs are there to set the hottest temperature you want the individual rooms to reach. There are ways to make systems work without TRVs but your house is a long way away from that. So you need TRVs in rooms that would otherwise get too hot as the system is heating up the cold rooms. You don't really need TRVs in the cold rooms. In my flat I have removed the TRVs from everywhere but the bedrooms and it works fine, but if I remove the TRVs from the bedrooms then the bedrooms overheat as the system is trying to warm up the cold other rooms. (My bedrooms have much better thermal properties - like your new bedroom in the old house)

Yes always on, the radiators should be hot/warm until the house is warm. Once the house is warm then you would expect the system to automatically turn on and off to maintain that temperature. You need to keep the system on to maintain a relatively steady temperature in your house. With thick walls like you have, once the heat is lost it takes an enormous amount of time and energy to heat up again so the key is to stop them getting cold in the first place. I've suggested you get a TRV fitted to your bedroom radiator. This way you can set your bedroom temperature independently from the rest of the house and set it a couple of degrees lower. But the system will still be on, pushing heat into the rest of the property.

I can't explain past decisions. What's important is to solve the problems now. Not at all. Traditional Gas systems usually have a controller (that might be near the cylinder) but a seperate thermostat somewhere central in the house. Heat pumps often by default have the thermostat inside the control screen. This should be installed in a place that is exposed to the coldest indoor temperatures (so it doesn't switch the heating off until the coldest place is warm). From what you've said your thermostat is near your cylinder, which explains your problem. The cylinder is mostly likely the hottest part of the house, so the thermostat is sitting there thinking it's 18C when you are sitting in the sitting room freezing. So either you need an engineer to attach a remote thermostat to your existing system or to move the existing thermostat.

That's pretty much what I came to as well. Glad to see it verified.