How to reduce heating bills without replacing your boiler or heating system.

Turn your heating flow temperature down — to the point the house is still warm

This is the biggest free saving on most homes, and almost nobody knows about it. A modern condensing boiler squeezes out extra heat by condensing the water vapour in its own flue gases — but that only happens when the water coming back from the radiators is cooler than about 55°C. Most combis leave the factory pushing out 70–80°C water, so the return never gets cool enough and that bonus is thrown away.

So on the boiler, find the central heating setting (separate from the hot water one) and turn it down. But here’s the part the simple advice skips: don’t aim for a fixed number — aim for the lowest setting at which your house still stays warm. Radiators give out heat in proportion to how much hotter they are than the room, so drop the flow temperature too far and they can’t shed heat fast enough to replace what the house is losing through its walls, windows and gaps. The pump can still move the water; the radiators just can’t get the heat into the rooms quickly enough — and the house cools down faster than the boiler warms it. It never quite gets there.

That tipping point depends on your home’s heat loss and how big your radiators are — undersized radiators need hotter water, which is also why a heat pump (running cool) usually needs bigger radiators or underfloor. The method is simple: turn the heating flow temperature down in steps over a few cold days. If the rooms still reach temperature, leave it; if they start falling short, you’ve gone a touch too low, so nudge it back up. The lowest setting your home is still comfortable at is the most efficient it can run.

(Weather compensation is meant to do exactly this for you automatically, by reading the outside temperature — but in most homes it turns out to be more trap than fix; more on why below.)

Set the hot water to the temperature you actually use

If you have a combi (no hot water cylinder), set the hot-water temperature to roughly what you use it at — around 39–42°C for showers, 50–55°C for baths. There’s no point burning extra gas to heat water hotter than that only to blend it back down with cold at the tap. A combi heats water on demand and stores none, so the legionella concern that applies to stored water doesn’t arise here. (If a bath takes an age to fill, that’s a flow problem rather than a temperature one — see water pressure boosting.)

If you have a hot water cylinder (a regular or system boiler), it’s different, because the water is stored. For legionella safety and the regulations the cylinder should sit at 60°C, and the boiler flow needs to be about 10°C above the cylinder setting — so around 70°C. That isn’t efficient (at 70°C the boiler barely condenses), but with stored water it’s the safe setting. It’s exactly why the heat-pump world does it differently: cylinders kept at 45–50°C day to day, with a periodic — usually weekly — pasteurisation cycle to deal with legionella, rather than holding 60°C around the clock.

The low-cost wins, roughly in order

• Set the room thermostat to comfortable, not maximum. Every degree lower is a real saving, and a jumper is cheaper than gas.
• Set your TRVs per room. The numbers on a radiator valve are rough target temperatures, not power levels — on most valves 1 is about 14°C, 2 about 18°C, 3 about 21°C, 4 about 24°C and 5 about 28°C (it varies by make, so follow the maker’s guide). Bedrooms can sit lower than the living room, and rooms you don’t use lower still.
• Heat the rooms you use to comfort, the rest to a low background level. Set unused rooms to about a 2 on the TRV on the same programmer times — warm enough to keep damp and frozen pipes away without paying to heat empty space. Keep doors to the cooler rooms shut.
• Bleed radiators that are cold at the top. Trapped air stops them filling, so the boiler works while half the radiator does nothing.
• Match the programmer to your actual day rather than running the heating round the clock.
• Draught-proof doors, windows and the letterbox — cheap, quick, and you feel it immediately.
• Insulate the easy things: loft insulation, a jacket on the hot water cylinder (it pays for itself in months), and lagging on exposed pipes.
• Reflective panels behind radiators on external walls, and keep furniture from blocking radiators.
• Close the curtains at dusk. They trap a surprising amount of heat against cold glass — just don’t let them hang over the radiators.

Heat the body, not the house

This is what I’ve told clients who were genuinely struggling, once I’d done everything I could to the system. If a house is leaking heat faster than you can afford to replace it, the cheapest thing of all is to stop trying to heat the whole house and warm only what actually needs to be warm — you. Keep the house at 14–16°C, or as low as you can comfortably tolerate, and warm yourself directly: an electric blanket or heated mattress topper, a heated throw on the sofa, plus jumpers, thick socks and warm trousers.

The numbers are firmly in your favour. An electric blanket draws a tiny fraction of what a boiler does, and every watt of it goes straight into keeping you warm rather than into a house that leaks it away. The heat stays where it’s needed and the bills drop as far as they can. There are obvious trade-offs — an unheated bathroom will feel cold — but warm drinks, a little localised heating where you actually sit and sleep, and decent layers all cost little and save a lot.

One sensible caveat: this approach suits able, healthy adults best. If anyone in the home is elderly, very young or unwell, keep at least the main living room a little warmer — the cold is harder on them.

A serviced boiler is an efficient boiler

A boiler with its combustion set correctly, the right gas pressure and no nagging faults runs at the efficiency it was designed for. One that’s never serviced quietly drifts — burning richer than it should, short-cycling, or fighting a tired pump or flat expansion vessel. A service costs a fraction of a replacement and is the cheapest way to keep an older boiler running at its best. More on what a proper service covers on my boiler repair and servicing page.

Controls that pay for themselves

Good controls do automatically what the flow-temperature trick does manually — keep the boiler running as cool and as little as it can while keeping you comfortable:

• Weather compensation — reads an outside sensor and aims to hold the flow temperature at the lowest that meets demand. On paper it’s the right idea, but in most homes it’s a trap: the radiators run cool, the house is slow to respond, and people feel cold and ask for the heating curve to be turned up, which throws the saving away. Real homes rarely help — few are designed perfectly, room use changes, and people feel the cold differently, one wanting it warmer while another opens a window.
• Load compensation — the system uses the residual heat already in the radiators, modulating the flow temperature to hold a steady comfort level on minimal gas.
• Smart and geolocation controls — the heating drops back when everyone’s out and is up to temperature by the time you’re home, using your phone’s location.
• Smart TRVs and multi-zone control — so you’re only heating the right rooms at the right times.

The brand I stand by is Heatmiser — it keeps working whether or not your internet does, which a cloud-only control doesn’t. I’ll also work with controls you already have. More on the integration side on my Electrical page.

Radiators cold at the bottom? That’s sludge

Radiators cold along the bottom, a system slow to warm up, or banging noises usually mean sludge — iron oxide from radiators that corroded internally because the water was never treated and no magnetic filter was fitted. The pump then circulates that grit around, blocking pipework and components and dragging efficiency down. The fix is a proper powerflush, a magnetic filter fitted, and the water dosed with inhibitor — done thoroughly, with the system water ending up as clean as the tap water, it shouldn’t ever need doing again.

One straight warning: on a heavily corroded system, cleaning the sludge out can occasionally expose pinholes it was plugging, which then leak and need repair. It’s uncommon, but I’ll always flag the risk before starting rather than after. And because Luton’s water is very hard, a scale reducer on the hot water side is worth fitting to keep limescale off the heat exchanger — part of the plumbing side.

If you can spend, cut the heat loss itself

Everything above gets the most out of the heat you’re already paying for. The bigger lever — if the budget stretches to it — is to stop the heat escaping in the first place. Double glazing and external (or internal) wall insulation cut a house’s heat loss at source: smaller bills, and just as usefully a house that stays warm at a lower flow temperature — so the boiler runs more efficiently and a heat pump becomes a far better fit. It’s the difference between heating a colander and heating a flask.

Get the numbers before you upgrade anything

If you’re thinking about bigger radiators, a different boiler or a heat pump, the money only works if it’s aimed properly. A room-by-room heat-loss calculation shows where the heat actually escapes and what each room really needs — so you’re not over-sizing kit, under-sizing it, or paying to heat air that’s leaking through gaps. It’s the difference between an upgrade that pays back and one that disappoints.

When replacing genuinely makes sense

None of the above turns a worn-out boiler into a new one. If yours is genuinely old, unreliable, and the repair bills are mounting, a modern boiler — or a heat pump if the property suits one — will use less and cost less to run, and it pays back over time. But that’s a decision for when you’re ready, not a default I’ll push you toward. Sort the free and cheap things first; they often buy you the time to plan the bigger move properly. When that day comes, see my boiler and heat pump pages.