How to Reset a Boiler Safely (and When Not To)

To reset a boiler safely, note the fault code first, check the pressure is above 1 bar, make sure gas is reaching the house and, if it's freezing outside, check the condensate pipe. Then press and hold the reset button, or turn the selector to reset, for the few seconds your manual gives, and give the boiler a few minutes to fire. A reset clears a lockout but doesn't fix what caused it. If the boiler locks out again after two or three tries, stop resetting and get a Gas Safe engineer to look at it.

Check these before you reset

A boiler locks out when its own safety checks find something wrong and it shuts down rather than carry on. Pressing reset tells it to try again. If the problem is still there, it will simply lock out again, so a couple of minutes of checks first makes a successful reset far more likely.

• Write down the code or light pattern. Take a photo of the display. The code is the most useful thing you can give an engineer, and some boilers clear it once you reset. Our boiler error codes guide explains what the common ones mean.
• Check the pressure gauge. Most systems need about 1 to 1.5 bar when cold. Below 1 bar, the boiler will usually refuse to run, and resetting won't help until you top it up. Follow our steps on how to repressurise a boiler first.
• Check the gas. Try the hob if you have gas cooking. If that won't light either, the problem is the gas supply or a prepayment meter that has run out, not the boiler.
• Check the power. Make sure the fused spur next to the boiler is on and the display is lit. After a power cut, check the timer and thermostat haven't lost their settings.
• Check the condensate pipe in cold weather. If the plastic pipe that runs outside has frozen, the boiler will lock out every time. Thaw it with warm (not boiling) water before resetting. Our guide to a frozen condensate pipe or blocked flue shows how.
• Check the thermostat is calling for heat. Turn the room thermostat up a few degrees above room temperature and make sure the timer is on.

How to reset a boiler

The exact button varies by make and model, so check the user manual if you have it. Most manufacturers publish their manuals online under the model name printed on the front or underneath the boiler. The general process on most modern combi and system boilers is:

Resetting common boiler makes

The principle is the same across brands, but the controls and the way the fault is shown differ:

• Worcester Bosch: many models show a code and a flashing light, and have a reset button on the control panel. If the blue light is flashing, see our guide to a Worcester boiler flashing blue light.
• Vaillant: ecoTEC models show an F code and have a reset button. F28 and F29 are ignition and flame-loss faults that often follow a gas supply problem. See our guides to Vaillant F28 and Vaillant F29.
• Ideal: many Logic and Vogue models show an F or L code and use a reset button or selector position. F1 is usually low pressure, covered in our Ideal F1 guide.
• Older boilers with a pilot light: these don't reset in the same way. If the pilot has gone out, follow the relighting instructions on the boiler or read our guide on a pilot light that keeps going out.

Why a boiler keeps locking out

If the boiler fires after a reset but locks out again later, something is still wrong. The usual causes are:

• Pressure dropping. If you keep having to top it up, there is a leak somewhere or the pressure relief valve is letting water go. See why a boiler keeps losing pressure.
• Ignition or flame detection faults. A worn ignition electrode, a flame sensor that needs cleaning or a gas valve fault will cause repeated ignition lockouts.
• Overheating. Sludge, a sticking pump or a partly closed valve can stop water moving through the boiler, so it overheats and shuts down. This is more common when the heating is first used after summer, because pumps and valves that have sat still for months can stick. Our guide on when to turn the heating on covers the checks worth doing before the first cold night.
• Flue or condensate blockages. A blocked condensate trap or a flue restriction stops the boiler running safely.

Our article on a boiler that keeps turning off goes through these in more detail.

When not to reset

Don't remove the casing to look inside, and don't try to bypass or reset any internal overheat stat. Anything inside the boiler must be dealt with by a Gas Safe registered engineer. If your boiler is under warranty, check the terms before booking, because manufacturers often expect their own engineers or your installer to do repairs during the guarantee.

When you do call, give the make and model, the code, the pressure reading and what you have already checked. It helps the engineer arrive with the right expectations. Our labour is £95 an hour, the £60 call-out is waived when the job runs over 2 hours, and we confirm the price before starting. Read more about our boiler repair service and boiler lockout repairs.

Frequently Asked Questions