Energy bills are set to rise again this October, with the price cap climbing by £63 to £1,717 for a typical household. That is the third increase in 2024 alone. Against this backdrop, any credible method to cut costs without freezing is worth a hard look.
A viral household hack, as reported by HuffPost UK, claims you can save £250 a year by simply tweaking your boiler’s flow temperature. The premise is straightforward: condensing boilers operate most efficiently when the return water is cool enough to condense vapour in the flue gases. Set the flow temperature too high, say 70°C, and the boiler cycles on and off, wasting gas. Lower it to around 55°C, and the boiler runs longer but at lower intensity, burning less fuel overall.
Who qualifies, and who doesn’t
This hack only works for homes with a condensing combi or system boiler, which covers roughly 80% of UK households. If you have an older non-condensing boiler, the efficiency gain is negligible. The same applies if you have radiators undersized for your home’s heat loss: lowering the flow temperature may leave rooms too cold. Energy Saving Trust advises checking your boiler’s manual first. Most modern boilers have a dial or digital setting for flow temperature, often labelled ‘CH’ or ‘central heating’. Turning it down to 55°C is safe and reversible.
But the catch is timing. In winter, when outside temperatures drop below 5°C, a flow temperature of 55°C may not heat your home adequately if radiators are poorly sized or your insulation is thin. The hack works best in spring and autumn, or as part of a broader retrofit. Ofgem’s data shows the average gas bill for a 3-bed semi is £1,100 a year; saving £250 is a 23% cut, significant, but conditional on the home’s fabric.
What it costs a typical 3-bed semi
The hack costs nothing to implement. You simply turn a dial or press a button. No installer call-out, no parts. The saving of £250 is based on a household using 12,000 kWh of gas per year, which is typical for a 3-bed semi with average insulation. If your home is draughty or has single glazing, the saving will be lower because you’ll need to run the boiler longer to compensate. The Energy Saving Trust estimates that draught-proofing alone can save £125 a year, so combining the two steps could push savings closer to £375.
On the EPC front, reducing gas consumption directly improves your carbon score. A 23% cut in gas use equates to roughly 0.6 tonnes of CO2 saved per year, enough to lift your EPC from a D to a C if combined with other measures like loft insulation. The government’s Boiler Upgrade Scheme offers £5,000 grants for heat pumps, but this hack is a cheaper interim step while you plan a full retrofit.
Real-world action: what to do this week
First, locate your boiler’s flow temperature setting. For most Worcester Bosch, Vaillant, or Ideal models, it’s a dial or digital menu option. Set it to 55°C for central heating. Leave the hot water temperature at 60°C to prevent legionella. Monitor room temperatures for a week: if they stay above 18°C, you’re fine. If not, nudge the flow up to 60°C and test again.
Second, pair this with a free energy audit from your supplier. Ofgem’s rules require all major suppliers to offer advice and support. You can also check your EPC at gov.uk, it costs nothing and reveals where your home loses heat. Third, consider a smart thermostat: installing one can save an additional £75 a year by optimising heating schedules. The catch is the upfront cost, typically £150–£200, but payback comes within three years.
Households on standard variable tariffs can start today. No application forms, no grants needed. But act before October’s price rise: every day of lower gas use compounds the saving. If you have a condensing boiler, this is the cheapest energy upgrade you can make. If you don’t, start with draught-proofing and a boiler service, and bookmark this hack for when you replace your boiler.
Frequently Asked Questions
No. Condensing boilers are built to operate at lower flow temperatures. Most manufacturers recommend a range between 50°C and 70°C. Setting it to 55°C is within safe limits and can actually reduce wear by preventing short cycling.
If your home stays warm (above 18°C) after lowering the flow, your radiators are adequately sized. If rooms feel cold, you may need larger radiators or improved insulation. A heating engineer can calculate heat loss using standard MCS methodology.
