How to reset a boiler, and when you should not
To reset a boiler, first check the simple things that cause a lockout: the power, the gas supply, the pressure gauge and, in cold weather, a frozen condensate pipe. Then use the reset control, which is usually a button marked reset or a dial turned to the reset position, and hold it for the few seconds your boiler manual gives. Try once or twice at most. If the boiler locks out again, stop resetting it, write down the fault code and book a Gas Safe registered engineer. If you can smell gas, do not reset anything: leave the controls alone and call the National Gas Emergency Service on 0800 111 999.
Loyal Plumbers · Updated
Discuss your plumbing workWhat a reset actually does
A modern boiler watches its own flame, temperatures, pressure and fan. When something falls outside safe limits, it shuts down and locks out, usually showing a fault code or a flashing light. The reset control tells the boiler to try again from the beginning.
That is useful when the cause was brief: a dip in the gas supply, a power interruption, air in the system or a condensate pipe that has since thawed. It is not a repair. If the underlying fault is still there, the boiler will simply lock out again, and repeated resets can make some faults worse or hide the pattern an engineer needs to see.
Check these before you press reset
A few quick checks often explain the lockout and mean the reset will actually hold. None of them involves opening the boiler casing, which should only ever be done by a Gas Safe registered engineer.
- Power: is the display lit, and is the fused switch next to the boiler on? A tripped circuit or a power cut can leave controls and timers out of step.
- Gas: do the gas hob or other gas appliances work? On a prepayment meter, check there is credit and the supply has not been cut off.
- Pressure: on a combi or system boiler, look at the gauge. If it is below the minimum in your manual, top it up through the filling loop before resetting.
- Controls: make sure the thermostat is set above room temperature and the timer or programmer is calling for heat.
- Weather: in freezing conditions, check the white or grey plastic condensate pipe running outside. Ice inside it is a very common cause of winter lockouts.
Where to find the reset control
Reset controls vary between makes and models, and even between boilers from the same manufacturer. The table covers the usual arrangements. The user manual, or the manufacturer's website, shows the exact method for your model; the model name is normally printed on the front panel or on a label underneath.
| What the boiler has | How the reset usually works |
|---|---|
| A button marked reset, or with a flame and cross symbol | Press and hold for the time given in the manual, often a few seconds |
| A mode dial with an R or reset position | Turn the dial to reset, hold briefly, then return it to its normal setting |
| A digital display with buttons | Follow the on-screen prompt or the manual's button sequence |
| A separate wireless or smart control | Some allow a reset from the control, but many still need the boiler itself |
Do not switch the boiler off and on at the mains as a substitute for the reset. Many lockouts are designed to survive a power cycle, and cutting the power mid-cycle can stop the pump from cooling the boiler down.
How many times should you try?
Once is reasonable, and a second attempt after checking the list above is fine. If the boiler locks out again soon afterwards, or shows the same code every day, the reset is only postponing the problem. Stop there.
Before you call, note the fault code or light pattern, when it happens (first thing in the morning, when hot water is drawn, in cold weather), what the pressure gauge reads and whether anything has changed recently, such as work on the pipes or a power cut. That record shortens the diagnosis and makes it more likely the engineer brings the right part.
Frozen condensate pipe: the winter lockout
Condensing boilers produce slightly acidic water, which drains away through a plastic condensate pipe. Where that pipe runs outside, it can freeze in a cold snap. The water backs up, the boiler detects it and locks out, often with a gurgling noise from the boiler before it stops.
If the frozen section is at ground level and safe to reach, pouring warm water from a kettle that has been left to cool slightly, or holding a hot water bottle against the pipe, will usually thaw it. Never use boiling water on the plastic, and never climb a ladder in icy weather to reach a high pipe. Once the pipe is clear, reset the boiler as normal.
A condensate pipe that freezes every winter is a design problem rather than bad luck. It may be too long outside, too narrow or not insulated. An engineer can reroute or upgrade it so the same lockout does not return with each frost.
When you should not reset the boiler
Some warning signs mean the boiler should be left off and not restarted. In these cases a reset is not a sensible first step, and in some it is dangerous.
- You can smell gas: do not touch switches or controls, open windows, turn off the gas at the meter if you can do so safely, leave the property and call 0800 111 999.
- A carbon monoxide alarm is sounding, or people in the home have headaches, dizziness or nausea that ease when they go outside.
- Water is leaking from inside the boiler casing, or there is scorching, sooting or a burning smell.
- The boiler makes loud bangs when it tries to light.
- The same lockout keeps returning after each reset.
Book a boiler engineer
Loyal Plumbers repairs boilers across London and everywhere inside the M25. Gas work is carried out by Gas Safe registered engineers, and with 10 vans working 24 hours a day we can often get to a boiler that will not stay on quickly, which matters in the first cold weeks of the heating season.
Call us or send an enquiry with the boiler make and model, the fault code, what the pressure gauge shows and what happened when you tried the reset. Our call-out charge is £60, and the engineer explains the fault and what the repair involves before any work goes ahead.
Common questions
- Is it safe to reset my boiler?
- Using the reset control as the manual describes is safe in normal circumstances. Do not reset it if you smell gas, a carbon monoxide alarm has sounded, or water is leaking from inside the casing.
- Why does my boiler keep needing to be reset?
- A lockout that returns has a cause the reset does not remove, such as low pressure, an ignition or flame fault, a blocked condensate pipe or a failing part. Record the code and book a diagnosis.
- My boiler has no reset button. What do I do?
- Many boilers use a dial position or a button combination instead. Check the user manual or the manufacturer's website for your model before trying anything else.
- How do I know if my condensate pipe is frozen?
- It usually happens in sub-zero weather. The boiler may gurgle, then lock out with a fault code. The outside section of the plastic pipe often feels solid or has ice at the end.
- Should I reset the boiler after a power cut?
- Often it restarts on its own. If it shows a fault, check the clock and timer settings first, then use the reset control once. Persistent faults after a power cut need an engineer.
Sources and further reading
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