Heating Dead After a Power Cut or Storm? Getting It Back On

If your boiler is not working after a power cut, the most common causes are a tripped switch at the consumer unit or fused spur, a timer or thermostat that has lost its settings, or a boiler that went into lockout when the power dropped. Work through those three in order and most heating systems come back on within a few minutes. If the power is on, the controls are calling for heat and the boiler still shows a fault after one reset, it needs a Gas Safe registered engineer.

A gas boiler cannot run without electricity. The fan, pump, ignition and control board all need power, so even a short outage stops the heating completely. Here is what to check, in order, once the lights come back.

Why boilers misbehave after a power cut

When the power fails, the boiler’s gas valve closes and everything stops. When power returns, most boilers simply restart and pick up where they left off. Some do not, for a few reasons:

• The supply never reached the boiler. A surge as the power returns can trip the RCD or a breaker in your consumer unit, or blow the fuse in the boiler’s fused spur.
• The controls are not calling for heat. Timers and programmers may have lost their clock or schedule, and wireless room thermostats may have lost contact with their receiver.
• The boiler is in lockout. If power dropped mid-ignition, or flickered on and off during a storm, the boiler may have registered a failed start and locked out as a safety measure.
• Something outside has changed. Storms often bring freezing temperatures, high winds and debris, which can freeze the condensate pipe or block the flue terminal.

As the OVO guide to boiler resets puts it, lockout means the boiler has shut itself down after detecting a problem, and resetting it without dealing with the cause will not help. That is why the order of checks matters.

Step-by-step: getting the heating back on after a power outage

1. Confirm the power is back for the whole house. Check lights and sockets in several rooms, especially the kitchen or wherever the boiler is.
2. Check the consumer unit. Look for any RCD or circuit breaker in the down or off position. Reset it once. If it trips again straight away, leave it off and call an electrician.
3. Check the fused spur. This is the switched socket-style plate near the boiler, often with a small red light. Make sure it is on. If the light is off and the rest of the circuit is live, the fuse may have blown. Our guide to a boiler with no power or a blank display covers this in more detail.
4. Look at the boiler display. Is it showing normal standby, a pressure reading, or a fault or lockout code? Write down any code before you do anything.
5. Check the pressure gauge. Most sealed systems sit around 1 to 1.5 bar when cold. Low pressure is not caused by a power cut but often gets noticed afterwards.
6. Check the timer and thermostat. Set the correct time, check the heating is on in the programme, and turn the room thermostat up a few degrees to make sure it calls for heat.
7. Reset the boiler once if it shows a lockout. Use the reset button or method in your user manual. See our guide to resetting a boiler safely.
8. Give it a few minutes. Some boilers run a self-check or anti-cycling delay before firing, so do not keep pressing buttons.

If the boiler fires and the radiators start warming, you are done. Reset the timer properly and check it again the next morning.

Reset timer after a power cut: mechanical, digital and smart controls

Controls are the most common reason for heating not working after a power outage, because the boiler itself is fine but nothing is asking it to run.

Many smart thermostats fall back to a basic schedule or frost protection if they lose internet, so the heating may run at odd times until they reconnect. If yours stays offline, our article on smart thermostats and boiler compatibility explains how they link to the boiler.

Boiler lockout after a power cut: when a reset is enough

A single lockout after a power cut or a flickering supply is not unusual and is often cleared by one reset. Vaillant’s guidance on resetting a boiler notes that some boilers take several minutes to reset or may need a second attempt, but if it still will not start or the error code stays, you should contact a Gas Safe registered engineer. Needing to reset regularly is not normal.

Reset codes and buttons vary by manufacturer. Look for a button marked with a flame and cross, a reset symbol, or a combined mode and reset button, and check your manual for whether it needs a short press or a longer hold.

Signs it is more than a power cut

• The boiler locks out again every time you reset it.
• You hear the fan run and clicking from the ignition, but no flame lights.
• The RCD or fused spur trips again when the boiler starts, which can point to a fault in the boiler’s electrics, pump or fan. See our guide to a boiler tripping the electrics.
• There is a burning or electrical smell, or water leaking from the boiler.

Any of these need an engineer. A power surge can occasionally damage a boiler’s printed circuit board (PCB), and diagnosing that safely requires removing the case, which is engineer-only work.

After a storm: outside checks that cause the same symptoms

Storm outages often come with freezing temperatures and strong winds, which can stop a boiler for reasons unrelated to the electricity.

• Frozen condensate pipe. If your boiler gurgles and locks out in sub-zero weather, the plastic pipe running outside to the drain may be frozen. Thaw it with warm (not boiling) water. Our guide to a frozen condensate pipe walks through it.
• Flue damage or debris. High winds can dislodge or crack a flue terminal or pile leaves and debris around it. Look from the ground only. Do not climb a ladder in bad weather, and do not use the boiler if the flue looks damaged.
• Water ingress. Driving rain can sometimes get into a poorly sealed flue. Water dripping from the boiler casing needs an engineer.

Keeping safe during a winter power cut

Losing heating in January is uncomfortable, and for older people, babies and anyone unwell it can be a real risk. While you wait for power or a repair:

• Never use a gas cooker or oven to heat a room, and never bring a barbecue, camping stove or outdoor heater indoors. They can produce carbon monoxide.
• Keep doors closed and gather everyone in one room.
• Make sure your carbon monoxide alarm has working batteries, since mains-powered alarms may not work in a power cut.
• Report the power cut to your local electricity network operator. GOV.UK lists 105 as the free number to call for a power cut or electrical hazard.
• If you smell gas, do not touch electrical switches, open doors and windows, leave the property and call the National Gas Emergency Service on 0800 111 999.

Still no heating? Book an engineer

If you have checked the power, the controls and the outside pipes and your boiler still will not run, our Gas Safe registered engineers can help. We offer a same-day emergency call-out across Stoke-on-Trent, Newcastle-under-Lyme, Kidsgrove, Stone and the surrounding area, subject to availability. Have the fault code and boiler model ready and contact Gasmaster to arrange a visit.

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