Is a power cut going to affect my boiler?

This is a collaborative post

Boiler malfunctions never come at the right time. It’s always going to be during the coldest January chill, or when you have elderly guests coming to stay. Knowing what can affect your boiler and heating system can make these issues slightly less daunting, and also help you figure out how to fix them. With that in mind, let’s take a look at how power cuts can affect your boiler. 

A quick answer

In short, yes. Even gas boilers rely on electricity for their control board, ignition, circulation pump and (on room-sealed models) the flue fan. When the electricity stops, the boiler won’t be able to function, so central heating pauses and, on a combi, so does instant hot water. The gas may still be perfectly able to flow; the appliance just has no electricity to allow all of its other functions to operate.

Combi versus system boilers

A combi only makes hot water when a flow sensor sees a tap open and the electricity lights the burner. No power means no sensor, no pump, no ignition - so you won’t have any hot water from your taps, and no heating from your radiators either. 

With a system or regular boiler feeding a hot-water storage container, the story is a little different. The tank may already hold a bath or two of hot water, so you may be able to use what’s stored, but you won’t be able to reheat it until the power returns. It’s also possible that the water won’t flow well, if it depends on an electric pump for heat.

What might still work during the power cut

Taps on a mains system should still be able to run cold water (unless your water is solely pressurised by a water pump), and a cylinder and radiators will hold heat for a while if it’s well insulated. 

Old gravity-circulation setups that run without a pump are rare now; unless an engineer from somewhere like Able Plumbing has told you otherwise, it’s best to assume your system needs power.

What happens when the power returns

Most modern boilers recover by themselves. Give it a minute, then check the fuses are still all flipped the right way, and look at the display. If you see a fault code, check the manual (and YouTube videos if necessary) to see what they mean. 

Next, have a look at the clock and any timers you’ve set. Even brief cuts can mean that it doesn’t know what time it is any more, so schedules may be an hour out and make the heating “mysteriously” late. 

Finally, check the pressure gauge on sealed systems; cold pressure should be around 1.0-1.5 bar typically. A power cut shouldn’t result in a drop in pressure, but if you bled radiators earlier, the boiler may refuse to fire until you top up via the filling loop, and it’s a good time to check it anyway.

Power cuts are annoying, and they can result in a break in your hot water supply. Unfortunately, there’s not much you can do about it, other than wait for the electricity to come back online.