To learn how to reset a boiler safely, start with one rule: fix or check the cause first, then press reset once. A reset clears a safety lockout so the boiler can try again, but it does not repair anything, and if the boiler locks out again the fault needs a Gas Safe registered engineer.
Quick answer: Make sure you cannot smell gas, note the fault code, then check the likely cause: top the pressure up to 1 to 1.5 bar or thaw a frozen condensate pipe with warm water. Press the reset button or use the reset menu as your manual describes. If it locks out again, call a Gas Safe engineer.
What Does Resetting a Boiler Actually Do?
A reset clears the lockout, not the fault. Modern gas boilers shut themselves down when they detect a problem such as low water pressure, no flame or overheating. This is called a lockout, and the boiler usually shows a fault code, a red light or a flashing symbol. Pressing reset tells the control board to try starting again.
If the cause has gone, for example because you have topped up the pressure or the gas supply has been restored, the boiler will start normally. If the cause is still there, it will lock out again, often within a few minutes. That second lockout is useful information: it tells you the problem needs an engineer, not another reset.
When Is It Not Safe to Reset a Boiler?
Never reset a boiler if you can smell gas or see any sign of carbon monoxide; call the National Gas Emergency number on 0800 111 999 instead. The Health and Safety Executive says it is illegal to use a gas appliance you suspect is unsafe, and that you should turn it off and leave it until a Gas Safe registered engineer has checked it. Do not reset if you notice:
- a smell of gas anywhere in the home;
- soot, scorch marks or black staining on or around the boiler;
- a lazy yellow or orange flame instead of a crisp blue one, on boilers where you can see the flame;
- headaches, dizziness, nausea or breathlessness in the household that ease when you go outside, which the Gas Safe Register lists as carbon monoxide symptoms;
- water leaking from the boiler, or a burning smell or loud banging.
How Do You Reset a Boiler Step by Step?
Work through these steps in order. Most lockouts that a homeowner can clear are caused by low pressure, a frozen condensate pipe or an interrupted gas or power supply.
- Check for danger first. If you smell gas or see the warning signs above, stop and call 0800 111 999.
- Write down the fault code. Look it up in your user manual or on the manufacturer’s website. Many codes tell you whether it is something you can check or a job for an engineer.
- Check the power and gas. Make sure the boiler’s fused spur switch is on, and check another gas appliance, such as the hob, works. On a prepayment meter, check there is credit.
- Check the pressure gauge. Ideal says normal cold pressure is 1.0 to 1.5 bar. If it is lower, top it up using the filling loop as your manual describes, or follow our guide on how to repressurise a combi boiler.
- In freezing weather, check the condensate pipe. This is the plastic pipe that runs from the boiler to a drain outside. If it is frozen, pour warm, not boiling, water over the frozen section at ground level, as Worcester Bosch advises.
- Press reset once. Use the method in your manual (see below), then wait a few minutes for the boiler to run through its start up.
- Test heating and hot water. Turn on a hot tap and the heating. If the boiler fires and stays running, you are done. If it locks out again, stop.
Where is the reset on my boiler?
Reset controls vary by model, so always follow your manual. The three most common types are:
- A dedicated reset button, often marked with a flame or the word reset. Baxi says to press it until the red lockout light goes out.
- A control knob or selector. On some Baxi models you turn the temperature knob fully anticlockwise until the lockout light goes out, or turn the selector to R and hold for at least 5 seconds.
- A display menu. On newer boilers with a text display, such as the Worcester Bosch Greenstar 8000+, the user instructions say to press the keys shown in the manual until Reset is displayed; the boiler then starts up again.
Safety: Your part stops at the outside of the boiler: the reset control, the pressure gauge and filling loop, the power switch and a frozen condensate pipe at ground level. Worcester Bosch’s user instructions state that only a competent engineer may remove the casing. Never open the boiler, touch the gas valve, flue or wiring, or keep resetting a boiler that keeps locking out. That is a job for a Gas Safe registered engineer.
How Many Times Should You Reset a Boiler?
Reset once after fixing the likely cause, and stop if the boiler locks out again soon after. Baxi says that if lockout occurs frequently, a fault is indicated and you should contact your installer or service engineer. Some manuals give a specific maximum number of attempts, so if yours does, follow it and never go beyond it.
Repeated resetting is not just pointless. Each failed ignition attempt is the boiler protecting itself and your home from a fault, and forcing it to try again and again can hide a problem that needs attention.
Why Does My Boiler Keep Locking Out?
Low pressure and frozen condensate pipes are the two lockout causes you can usually clear yourself; most other causes need an engineer.
| Likely cause | Typical sign | What you can do | Who fixes it |
|---|---|---|---|
| Low system pressure | Gauge below 1 bar, pressure fault code | Top up to 1 to 1.5 bar, then reset | You; an engineer if it keeps dropping |
| Frozen condensate pipe | Freezing weather, gurgling, ignition or flame code | Thaw with warm water at ground level, then reset | You; an engineer if the pipe needs rerouting |
| Gas supply off or no meter credit | Hob will not light either | Check meter and credit, contact supplier | You or your gas supplier |
| Power cut or tripped switch | Blank display | Restore power, then reset if needed | You; an electrician if it keeps tripping |
| Ignition or flame fault | No flame code returns after one reset | Nothing further | Gas Safe registered engineer |
| Overheating or poor circulation | Overheat code, banging or kettling noises | Check pressure only | Gas Safe registered engineer |
| Flue or fan problem | Flue or air pressure code | Nothing; do not touch the flue | Gas Safe registered engineer |
When Should You Call a Gas Safe Engineer?
Call a Gas Safe registered engineer if the boiler locks out a second time after you have checked the pressure, gas, power and condensate pipe. Manufacturers are clear that most fault codes are not DIY jobs; Vaillant’s fault code page repeats the warning that it is “a case for an expert” against each code. Book an engineer straight away if:
- the same fault code returns after one reset;
- you need to top up the pressure more than once or twice a year, which Ideal says is worth having investigated;
- water is leaking from the boiler or pipework;
- the manual says the code needs a service engineer;
- the boiler is noisy, smells of burning or shows any of the danger signs above.
If your boiler is a Worcester Bosch showing EA, our Worcester Bosch EA error code guide walks through that lockout in detail.
Worked Example: A January Lockout
Example: a combi boiler locks out on a frosty January evening. The homeowner checks there is no smell of gas and the gauge reads 1.2 bar, so pressure is fine. The condensate pipe outside is frozen solid at ground level. Warm water poured over it clears it, reset is pressed once and the boiler fires. The next morning it locks out again with the same code, so the homeowner does not reset again and books a Gas Safe registered engineer.
While waiting a day for the visit, the homeowner heats one room with a 2,000 W electric heater for 5 hours. That uses 2 kW × 5 hours = 10 kWh. At the October to December 2026 price cap rate of 26.32p per kWh, it costs 10 × 26.32p = £2.63 for the day. You can check the same numbers with our electricity cost calculator by entering 2,000 W and 5 hours a day, or read our guide on how to calculate appliance running costs. Use any portable heater on a flat surface, away from curtains and furniture, and never leave it running unattended.
How to Reset a Boiler FAQs
Is it safe to reset my boiler myself?
Yes, using the reset button or menu described in your manual is a normal user task, as long as you cannot smell gas and there are no signs of carbon monoxide or leaks. Never remove the casing; anything inside the boiler needs a Gas Safe registered engineer.
How long should I hold the boiler reset button?
It depends on the model. Baxi says to press the reset button until the red lockout light goes out, or hold the selector at R for at least 5 seconds. Other boilers reset through a display menu. Check your user manual for the exact method.
Why won’t my boiler reset?
A boiler will not stay running if the cause of the lockout is still there, such as low pressure, a frozen condensate pipe or no gas supply. If you have checked these and it still locks out, there is a fault that needs a Gas Safe registered engineer.
Should I switch my boiler off and on to reset it?
Some manufacturers suggest switching off and back on after clearing a frozen condensate pipe, while most lockouts need the reset button or menu. Follow your manual. Switching the power on and off repeatedly will not clear a genuine fault.
What pressure should my boiler be at before I reset it?
Ideal gives a normal cold operating pressure of 1.0 to 1.5 bar. If the gauge is below 1 bar, top up using the filling loop first, then reset. If the pressure keeps falling, there may be a leak that needs an engineer.
Can I reset my boiler if I smell gas?
No. Do not reset or use any gas appliance. Call the National Gas Emergency number on 0800 111 999, open doors and windows, and turn off the gas at the meter if you can, as the Health and Safety Executive advises.
For more tools on heating costs and sizing, visit our heating calculators hub.
Checked October 2026. Sources: Baxi: How to reset a Baxi boiler, Worcester Bosch: Greenstar 8000+ user instructions, Worcester Bosch: Frozen condensate, useful information, Ideal Heating: Topping up boiler pressure, Vaillant: Boiler fault codes, HSE: Domestic gas safety FAQs, Gas Safe Register: Carbon monoxide poisoning, Ofgem: Energy price cap rates.
