Backup power for a gas boiler
To run a boiler and its pump for 8 hours without power you need about 1,1 kWh of battery and a unit that survives a 730 W start. Answer a few questions and we will find you a specific model with its price.
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The location determines what kind of equipment can go there.
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Back to the questionsHow much battery a boiler needs
Battery capacity for each set of appliances and each outage length. On the right, the start the station or inverter has to survive.
| What keeps running | 4 h | 8 h | 12 h | 24 h | Start |
|---|---|---|---|---|---|
| Boiler with its circulation pump | 530 Wh | 1,1 kWh | 1,6 kWh | 3,2 kWh | 730 W |
| Boiler, router and lights | 650 Wh | 1,3 kWh | 1,9 kWh | 3,6 kWh | 750 W |
| Boiler, router, lights and fridge | 940 Wh | 1,8 kWh | 2,7 kWh | 5,4 kWh | 1,3 kW |
With its pump the boiler draws up to 180 W, but the burner and the pump do not run all the time, so the average comes to 96 W. The figures already include about 37% of headroom for inverter losses, partial discharge and battery ageing.
What to know about powering a boiler
Why a boiler stops when the power goes
A modern gas boiler is run by electronics: they light the gas, watch the flame and drive the fan and the pump. Without electricity the boiler stops even though the gas is still there. Boilers that need no power do exist, but if the heating has a pump, it still needs power.
How much it really uses
Add up the rating plates of the boiler and the pump and you get about 180 W. But the burner and the pump do not run all the time, so on average the boiler draws about 96 W. That is how we size it: 8 hours comes to 1,1 kWh, not twice that, which is what the rating plate would give you.
A pure sine wave is a must
Boiler electronics are sensitive to the shape of the voltage. On an inverter with a modified sine wave the boiler may throw errors and the pump may hum and run hot. Get a station or inverter with a pure sine wave, and check the specification before you buy.
The boiler may not see its flame
Many boilers detect the flame by ionisation, and for that they need live, neutral and earth connected properly. On a station or inverter without an earth such a boiler sometimes reports an ignition fault even though everything is plugged in correctly.
Earthing, or a bond between neutral and earth on the inverter's output, usually fixes it. That is a job for an electrician, not one to do yourself.
A station or an inverter with batteries
If the boiler has a plug, a power station can run it: move the plug and it works. For outages of 4 to 12 hours that is the simplest answer.
If the boiler is wired into the consumer unit with no plug, or outages last a day or more, an inverter with batteries is more practical. It switches over by itself when the power goes, so the boiler keeps running even at night. Some stations have a UPS mode too, but their switchover times differ, so check the specification.
What else to bear in mind
- Winter outages often come one after another. The station has to recharge in between, so look at charging speed as well as capacity.
- Keep the station somewhere warm. In the cold a battery gives less, and most stations will not charge below freezing.
- A domestic gas boiler is single-phase, so three phases in the house change nothing: an ordinary single-phase station or inverter will run it.
If the boiler is in a flat, see also which station to choose for a flat: the fridge, the kettle and recharging between outages.
Common questions about boilers
How long will a 1 kWh station run a boiler?
A boiler with its pump draws about 96 W on average, so a 1 kWh station keeps it going for roughly 7,5 h. That allows for inverter losses and for not running the battery down to zero. Put the router, lights and fridge on the same station and the time falls by almost half.
Can I connect the boiler to a station myself?
If the boiler has a plug, yes: you move the plug into the station's socket. If it is wired into the consumer unit with no plug, you first need an electrician to give it a socket of its own or to connect an inverter to the consumer unit.
Why does the boiler show an error when it runs on a station?
Most often because of earthing: the boiler cannot see its flame when there is no link between neutral and earth on the station's output. Less often it is a modified sine wave. An electrician fixes the first; only a different source with a pure sine wave fixes the second.
I have three phases. Will the boiler work?
Yes. A domestic gas boiler is single-phase, so an ordinary single-phase station or inverter runs it. Three phases only matter if you want to back up the whole consumer unit.
How much does backup power for a boiler cost?
It depends on how many hours you need and what else has to run. For the boiler to run for 8 hours you need a station of about 1,1 kWh. The quiz above shows specific models with current prices, and it already knows you have a gas boiler.