'Only heating one room' - logistics

[RenegadeKeeblerElf]

I'm trying to get my head around the best way to be efficient with our gas use, and I want to make sure I am clear on the underlying mechanics of how it works.

I have a thermostat in the hallway that we can use to set a maximum and minimum temperature, and a programmable unit in the airing cupboard upstairs where I can set the times I want the hot water and heating to be on. During the times that the heating is 'on' it will actually only switch on if we are below the minimum temp as per the thermostat, and switch off when the max is reached. We have radiators in each room which also have dials to turn them up or down. So far, so simple, right?

However, what I am not clear on is how to make sure that I am getting the rooms we are using to a decent temperature without using more gas than we need to. If the boiler is either on or off, does it matter what temperature each individual radiator is set to? Will having some off/low really make any difference if the boiler is still going on to heat the rooms where the radiators are turned to the max? And if heating all the radiators uses the same amount of gas, wouldn't it be better to keep the whole house warm so we don't leak warm air into the cold rooms? Or does the boiler have to work harder to heat more radiators and therefore it is actually better to switch off the ones we don't use?

Secondly, since the thermostat is in the hallway, I presume that is the room/space whose temperature triggers the overall on or off of the system, so if we turn off the radiators in the hallway then the heating will be on more than we need it (as the hallway will be colder than rooms which are being heated) but if we have that radiator on then we are heating a space which doesn't really need to be warm, so which is best?

Sorry if this sounds stupid, I promise I am an intelligent adult, I just have a tenancy to overthink things and want to be sure I am getting this right!

does it matter what temperature each individual radiator is set to?

I saw a TikTok video on this last night. The heating engineer said if you use thermostatic valves on radiators correctly you will save the most money. I can’t find the video again now but he was saying if you turn them down on the rooms you aren’t using in the day, even turn the bedroom ones down whilst sitting downstairs and just pop up and turn them up an hour before you are going to bed, then you will save the most money. He actually said if you are heating half of your radiators you will halve your heating bill which makes sense I suppose. In reality it means you have to remember to turn your radiator and bathroom valves down when you get up and go downstairs, dash up and turn the bathroom one on before you have a shower at night, remember to turn the bedroom one on whilst watching the 10 o’clock news etc

Re the thermostat the advice is to turn it down, even 1 degree lower can result in £££ saved but I do see what you are saying about the hall radiator, it will definitely trigger the heating more if it’s colder there so better to leave the hall one on. Also, if your tap water is very hot, turn the water temp down on the boiler. If you are having to add cold to wash your hands then it’s too hot.

Fab thanks. All theoretical at the moment as obviously the heating is off but just want to make sure we are as efficient as possible in winter.

If your hall is a lot cooler than your living room then presumably your living room gets too warm as the boiler is constantly firing up to try and get to the temperature that is set in your hall. If I moved my thermostat to the hall or kitchen, I would have to set it to about 14 degrees otherwise the rest of the house would be like an oven unless I turned the radiators down.

I have the bedroom trvs set to 3 unless it’s below freezing for days.
My boiler flow temp is set to 62 degrees, my hot water to 55.