TRV's help but the main part is having thermostat in a habitable room. Hallways are naturally colder than bedrooms and lounges. Ideally you want it in the living room, a trv or a remote thermometer eve in there if you wanted to monitor the temp in her room
A trv is just a radiator valve with controls on them. Lots of different looks to them but basically like this:
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You don't need them but they're useful for reducing the demand on your boiler. Eg my office is warm because of computer and me being in it all day so doesn't need heat so that can easily go on frost or 1, so when heating comes on it's got less radiators to fill or keep as hot so less gas burned to do it
Most rooms fine at 2 (15c) or 3 (20c) - it stops rooms getting too hot when the main room is still being heated eg a small bedroom at a 3 and a lounge at a 3 - the bedroom hits 3 quickly so you don't want it to keep going to 24c because the lounge is still at 19c. Hallways etc you tend to leave on 5 as they're usually opened to the elements and have stairway etc so harder to heat
Have you checked the pre heating setting? Like I said £10-£15 a day is a lot on gas, we would have to have our boiler on most of the day AND firing constantly to hit those levels.
Speaking to similar houses is interesting but majority of people aren't really up to speed on efficiently heating a house as most people just do what they've always done or tweak it without learning how their system works most efficiently
Our £5 a day on electricity is 2 of us in a 4 bed detached however we have every device going - 1000w subwoofer, 200w stereo power amp, 200w surround sound amp, smart lighting all round the house and garden, 9 Alexa devices, work laptop, desktop computer, ps5 console, NAS/Media server, dehumidifier, dishwasher etc I think our elec use is definitely above average although have scheduled run times for some things to bring them down when not in use.
Bespoke instructions for turning off the pre-heat on any Vaillant combi boiler to save 5-10% on your gas bill.
www.theheatinghub.co.uk