Energy bills climb when the cold arrives, and the usual advice is to “put on a jumper” or nudge the thermostat down. I didn’t do either. I kept my home at the same cosy 20°C and still cut £150 from my winter gas spend, simply by stopping heat from leaking and making my boiler work smarter, not harder.
The radiators were doing their best, but the house felt like a train station — warm patches, gusty draughts, and that nagging sense of money drifting out through invisible cracks. I made tea, watched the smart meter blink, and thought: enough. That weekend I decided to treat heat like a guest I actually wanted to stay. I would keep the thermostat exactly where it was — and change everything around it.
I didn’t touch the thermostat once.
The bill that blinked first
My goal wasn’t heroic. Trim a chunk off the winter bill without sacrificing comfort. The win came from small, almost boring tweaks: draught-proofing doors and windows, lowering the boiler flow temperature, balancing radiators, and zoning our routine. The room temperature never changed. The behaviour of the house did. By late January, my gas use chart looked different — not dramatic spikes, just steady, smaller humps. That’s where the £150 went: into the gaps I sealed and the inefficiencies I calmed.
Here’s a concrete number. Last winter’s gas usage over 12 chilly weeks was 3,950 kWh. This winter, with the thermostat pinned to 20°C and the same family habits, it was 2,690 kWh — adjusted with local degree days so I wasn’t cheating by picking a milder season. At roughly 7.5p per kWh under the price cap, that’s close to £95 saved from consumption right there. Add fewer hot water cycles, a better boiler setting, and the letterbox brush I should’ve fitted years ago, and the running tally ticked past £150. Not a miracle. Just less waste.
The logic is simple. Heat leaves faster through gaps than most of us imagine, and modern condensing boilers only hit their stride when the water returning to them is cool enough to condense. Lowering the boiler’s flow temperature to 55°C let the system run longer, gentler cycles in its efficient zone. Radiators felt warm rather than scorching, the rooms held temperature without yo-yoing, and the boiler stopped short-cycling like a caffeine addict. The thermostat stayed at 20°C. The house learned a better rhythm.
What I actually changed, step by step
I started with the leak points. Foam strips on sash-windows, a brush and flap on the letterbox, keyhole covers, and a simple door brush on the draughty back door. A chimney balloon in the unused fireplace was the surprise star — the living room stopped gulping air like a lung. I slid radiator reflector foil behind two rads on external walls. Then I lowered the boiler flow temperature from 70°C to 55°C and bled the radiators. Finally, I set our thermostatic radiator valves so bedrooms ran cooler by default and doors stayed closed. No drama. Just routine, layered in.
Common pitfalls? Dropping the flow temperature too far, too fast. Try 60°C, live with it for two days, then nudge down if rooms still hit target. Forgetting to balance radiators is another trap: the first rad near the boiler hogs the heat while the last limps. Open lockshield valves a quarter-turn at a time, and give each room 30 minutes to show you what changed. Don’t cover radiators with laundry or sofa backs. And don’t block trickle vents you actually need for ventilation. Let’s be honest: nobody really does that every day.
Here’s what made it click for me: change the system, not the setting. Small physical fixes stack up fast.
“If your boiler returns cooler water, it can condense more and recover more heat. That’s free efficiency. You’re not making the house colder; you’re making the boiler happier,” said a local heating engineer who checked my settings.
- Draught-proofing kit: £25–£40, one afternoon
- Letterbox brush + keyhole covers: under £20
- Chimney balloon: ~£20, quick fit, big impact
- Boiler flow temp: 55–60°C for many systems
- Radiator bleed + balance: free, just time and a key
- Thermal curtain or door curtain: modest cost, instant comfort
The quieter kind of warmth
By February, the house felt calmer. Radiators whispered instead of clanging. The hallway no longer draft-dodged our ankles. We cooked, read, slept — same thermostat, smaller bill. We’ve all had that moment where a room feels warmer than the number suggests; this was that, on repeat. The living areas held heat between cycles, so the boiler worked less for the same comfort. Friends noticed the front room didn’t have that “Victorian breeze” anymore. *Heat rose, stayed, and suddenly the place felt like it was on our side.* I kept checking the smart meter out of habit — and smiling at its boredom.
| Point clé | Détail | Intérêt pour le lecteur |
|---|---|---|
| Lower the boiler flow temperature | Set to 55–60°C so a condensing boiler runs efficiently | Same thermostat setting, less gas used |
| Stop the leaks | Draught strips, letterbox brush, door sweeps, chimney balloon | Cheapest warmth is the heat you keep |
| Balance and zone | Bleed radiators, tweak lockshields, close doors, use TRVs | Even rooms, fewer boiler cycles, more comfort |
FAQ :
- Is lowering boiler flow temperature the same as turning the thermostat down?No. The thermostat controls room temperature. Flow temperature controls how hot the water in your radiators gets. You can keep 20°C on the wall and still run cooler water for better boiler efficiency.
- How much did all this cost?About £80–£120 for sealing kits, a chimney balloon, and a couple of thermal touches. The rest was time: bleeding, balancing, and adjusting boiler settings.
- Will rooms take longer to heat with a lower flow temperature?Often yes, a little. Then they hold heat more evenly. The result is steady comfort rather than sharp peaks and dips, which saves energy.
- What if I have a heat pump?Great news — heat pumps love low flow temperatures. Focus on insulation, draught-proofing, and gentle, continuous heat. TRVs still help to zone spaces.
- Is it safe to block an unused chimney?Use a purpose-made chimney balloon or cap and keep slight ventilation to avoid moisture build-up. If the fireplace is active or could be, don’t block it.
