The cheapest kilowatt-hours of all
Before insulation, before heat pumps, before anything with a price tag: most UK homes run their heating on settings nobody has touched since the system was installed. The boiler is set hotter than it should be, the thermostat higher than anyone needs, the radiators full-blast in rooms nobody uses. Fixing this costs an afternoon and routinely trims 10–20% off the heating bill — a better return than any hardware purchase on this site, because the outlay is zero.
The control trio
A properly controlled system has three parts, and the EPC model awards points for each:
- A room thermostat sets the target temperature for the house. Every 1°C lower saves roughly 10% of the heating bill — so find the lowest setting the household is genuinely comfortable at (typically 18–20°C) rather than defaulting to 21–22°C. Keep it clear of radiators, sunlight and draughts, all of which fool it.
- A programmer or timer matches heating to occupancy. Heat the house when people are in it and awake; let it coast when they’re not. Half an hour before waking and off half an hour before leaving/bed is the classic pattern.
- Thermostatic radiator valves (TRVs) set each room’s level individually. Spare rooms and hallways don’t need living-room temperatures: setting little-used rooms to 2-ish (roughly 15°C) and keeping their doors closed saves real money without letting the fabric get damp-cold. One exception: the room holding the main thermostat should have its radiator fully open (or no TRV), otherwise the two fight and the boiler short-cycles.
The flow-temperature trick
Modern condensing boilers only achieve their advertised ~90% efficiency when the water returning to them is cool enough to condense the flue gases — below about 55°C. Most are installed with flow temperatures of 70–80°C, which never lets that happen. On a combi boiler, turning the heating flow temperature down to 60°C or below (the radiator-symbol dial or menu setting) typically saves 6–8% of gas for nothing: rooms reach exactly the same temperature, just slightly more slowly. It’s free, reversible, and if the house struggles on the coldest week of the year, turn it up for that week.
Two related settings: on a combi, the hot water temperature is a separate dial — around 50°C is plenty for taps and avoids scald-mixing with cold. On a system with a hot water cylinder, store at 60°C (legionella safety — don’t go lower), put the cylinder on a timer rather than 24/7, and give it a £20 insulation jacket if it’s warm to the touch.
Two persistent myths
- “Leaving the heating on low all day is cheaper than timed bursts.” For nearly every home, no — a house loses heat in proportion to how warm it is, so every hour spent hot-while-empty is pure loss. Timed heating wins; the all-day approach only approaches parity in the most heavily insulated homes.
- “Cranking the thermostat heats the room faster.” A thermostat is a target, not a throttle — the boiler works at the same rate either way. Cranking it just overshoots (and wastes) later.
Smart thermostats, honestly
A smart thermostat (£150–£250 plus install) saves money only by changing behaviour — automatic setback when the house is empty, easier scheduling, per-room control on the fancier systems. If the household already runs a sensible schedule, the gain is small; if the current “schedule” is a manual on/off switch and guesswork, the gain is real. A £25 programmable thermostat captures most of the benefit; the smart version adds convenience. Either way it’s a nice-to-have — the free settings above come first.
Heat pumps play by different rules
Everything above assumes a boiler. A heat pump runs “low and slow” — steady output at low water temperatures, often near-continuously in cold weather — and is most efficient run that way. Big timed setbacks, aggressively zoned TRVs and boiler-style habits all hurt its efficiency; a well-set-up system uses weather compensation (water temperature follows outdoor temperature) and mostly wants leaving alone. If you have a heat pump and boiler habits, ask the installer to walk you through the controller — it’s the cheapest efficiency upgrade available.
The one-line summary
Lowest comfortable thermostat setting, heating timed to occupancy, TRVs turned down in unused rooms, and the boiler flow temperature down to ~60°C — an afternoon of free adjustments worth 10–20% of the heating bill, before spending a pound on hardware.
Related guides & tools
- Insulation and draught-proofing — the other cheap wins, and the step that comes next
- Heat pumps vs gas boilers — where the control logic changes completely
- EPC ratings — the control trio scores easy points on the certificate
- Smart tariffs and EV charging — after when you heat, when you buy electricity
Last reviewed: July 2026.