How much does a gas combi boiler cost to run?
About 1.3p an hour in the UK and 0.94¢ an hour in the US. A gas combi boiler draws about 85 W for roughly 60% of the time it is switched on, so it averages 51 W. The gas makes the heat, so a battery only has to run the fan, pump and controls. Most boilers are wired into a fused spur rather than a plug, and some will not light on a station’s ungrounded output — read the boiler guide before relying on it.
What it costs, by how long it runs
| Running for | kWh | UK | US |
|---|---|---|---|
| 10 minutes | 0.008 | 0.22p | 0.16¢ |
| An hour | 0.051 | 1.3p | 0.94¢ |
| An 8-hour night | 0.41 | 11p | 7.5¢ |
| A full day (24 hours) | 1.22 | 32p | 22¢ |
| A month at 8 hours a day | 12.24 | £3.22 | $2.24 |
UK prices use the Ofgem price cap for 1 October to 31 December 2026 (direct debit, average across England, Scotland and Wales, with no VAT on electricity this winter): 26.32p per kWh (Ofgem). The standing charge of 54.83p a day is paid whatever you run, so it is left out. US prices use the US average residential price for June 2026 from the Energy Information Administration: 18.34¢ per kWh (EIA). Your own tariff is on your bill; scale the figures by it.
Measure your own
These are typical figures for a typical unit. A plug-in energy monitor between the socket and the appliance shows the real watts and adds up the kWh, so after a day or a week you know exactly what it costs on your tariff.
Compared with similar appliances
| Appliance | Average W | UK per hour | US per hour |
|---|---|---|---|
| Electric blanket | 21 | 0.55p | 0.39¢ |
| Heated throw | 40 | 1.1p | 0.73¢ |
| Gas combi boiler (its electrics) | 51 | 1.3p | 0.94¢ |
| Gas furnace (blower and controls) | 300 | 7.9p | 5.5¢ |
| Space heater, 750 W | 750 | 20p | 14¢ |
| Oil-filled radiator | 900 | 24p | 17¢ |
| Space heater, 1,500 W | 1,500 | 39p | 28¢ |
| Space heater, 2,000 W | 2,000 | 53p | 37¢ |
| Fan heater | 2,000 | 53p | 28¢ |
Running it in a power cut
See which power station will run a gas combi boiler, and for how long.
Appliance draw modelled on professional.vaillant.co.uk. Vaillant’s ecoTEC plus installation manual lists the 825, 832 and 835 combis at 35 W minimum, 80–90 W maximum and under 2 W on standby; the 838 peaks at 120 W. Worcester Bosch’s Greenstar 4000 ErP data gives 39 W at full load and 13 W at part load. The gas does the heating; this is only the fan, pump and controls.
Did this match what you measured?
Nothing is sent anywhere unless analytics is switched on, and no text is collected.