No hot water after a power cut
Power cuts are an unfortunate fact of life in the UK, and they can leave your boiler in a bit of a state. When the electricity goes out and then returns, modern boilers — particularly condensing models — automatically enter lockout mode as a safety measure. This is actually sensible design, but it does mean you'll need to get your boiler firing again manually. The good news is that in most cases, this is a straightforward job that doesn't require a Gas Safe engineer's visit. This guide walks you through the reset process, pressure checks, and programmer settings so you can restore your heating and hot water without fuss. If you've followed these steps and your boiler still won't cooperate, or if you suspect electrical damage, that's when a qualified Gas Safe engineer should take a look.
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Most likely cause & what to check
After a power cut, most modern boilers go into lockout and need manually resetting.
Locate the reset button on your boiler and press and hold for 3–5 seconds.
Check your programmer — these often reset to factory defaults after a power cut.
Check boiler pressure — repressurise to 1–1.5 bar if below 1 bar.
If the boiler still won't fire, a power surge may have damaged the PCB — a Gas Safe engineer should inspect it.
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Frequently asked questions
Why does my boiler stop working after a power cut?
Modern boilers have safety lockouts that activate when power is lost and restored — it's a built-in protection to prevent dangerous operation. Your boiler essentially goes into standby mode and waits for you to manually reset it before it will fire up again.
How long does it usually take to reset a boiler?
The reset itself takes only seconds — usually a 3–5 second hold on the reset button. However, you should allow a few minutes for the boiler to cycle through its checks before it fires up properly.
What should I do if the reset button doesn't work?
Check that your boiler is receiving power — look for indicator lights or a display panel. If it has power but won't reset, the pressure may be too low, or the programmer may need attention; work through the pressure and programmer checks in the guide before calling an engineer.
Can a power surge damage my boiler permanently?
Yes, a significant power surge can damage the printed circuit board (PCB), which is the boiler's brain. If your boiler won't reset and shows no signs of life, or if it resets but won't fire after a few attempts, a Gas Safe engineer should diagnose whether the PCB has been affected.
Do I need to bleed air from my heating system after a power cut?
Not always — a power cut alone won't introduce air into your system. However, if your boiler pressure has dropped significantly, you may have a slow leak, which could allow air in over time; check the pressure gauge and repressurise if needed.
Why has my heating timer reset to the wrong time?
Most programmers use battery backup, but if yours has completely reset to factory defaults, the battery may have failed or discharged during the outage. Simply reprogram it with your preferred heating schedule — it's a quick job and separate from the boiler reset itself.