How to Reset a Boiler, and When You Should Stop Trying

What a reset actually does

A modern boiler watches itself constantly. If something falls outside safe limits while it is running, such as no flame being detected when it tries to light, the water inside overheating, or the flue not clearing properly, it shuts the burner down and locks itself out. The display shows a fault code, a flashing light or a flame symbol with a line through it, and the boiler will not try again on its own.

The reset button is how you tell the boiler you have seen the lockout and want it to have another go. It does not repair anything. It clears the lockout so the boiler can repeat its start up sequence. If the cause was a one off, like a brief dip in the gas supply or a power cut in the middle of a cycle, the second attempt usually works. If the cause is still there, the boiler will lock out again, often within a minute or two.

That is also why it is safe to press. A reset only lets the boiler try again with all of its safety checks still in place. It cannot override them.

Before you press reset: four quick checks

Some of the most common reasons a boiler stops are not lockouts at all, and a reset will not help with them. Spend a minute on these first.

• Power. Is the display lit? If it is blank, check the fused switch on the wall next to the boiler and the circuit breaker in the consumer unit. A boiler with no power has nothing to reset. If the power has just come back after an outage, our guide on a boiler not working after a power cut covers the extra checks.
• Gas. Are the hob or other gas appliances working? If not, the problem may be the supply or a prepayment meter that has run out of credit, not the boiler.
• Pressure. On a combi or system boiler, the gauge should normally read somewhere around 1 to 1.5 bar when the system is cold. Well below that, many boilers refuse to run and show a low pressure code. That needs topping up, not a reset.
• Controls. Is the programmer or thermostat actually asking for heat or hot water? After a power cut, many timers lose their settings and simply sit at off.

How to reset a boiler, step by step

If your boiler has no obvious reset control, look at the manual, which for most makes is available as a download if the paper copy is long gone. The model name is normally printed on the front or on a data plate underneath.

• Note down the fault code or the pattern of lights before you do anything. If you end up calling an engineer, this is the most useful thing you can tell them.
• Find the reset control. It is usually on the front panel, sometimes behind a drop down flap, and marked with the word reset, the letter R, or a flame symbol with an arrow.
• Press it once, or hold it for the time your manual gives. Some boilers want a single press, some want it held for around five seconds, and some reset by turning the mode dial to the R position and back.
• Wait two to three minutes. You may hear the fan run, a clicking from the igniter, then the burner lighting. Do not keep pressing during this time.
• Run hot water from a tap or turn the heating up to check it is actually working, not just showing a normal display.
• If it locks out again, wait five minutes and try one more time. If it fails a second time, leave it off and call an engineer.

Do not reset the boiler if you can smell gas, if a carbon monoxide alarm is sounding, or if water is leaking from the casing. Our guide to a carbon monoxide alarm going off explains what to do instead, and how to turn off a boiler covers shutting it down safely.

Where the reset is on common makes

The layout varies between models even within one brand, so treat this as a guide to where to look rather than an exact instruction for your boiler. The manual always wins.

• Worcester Bosch: most Greenstar models have a reset button on the front control panel, and many need it pressed and held for a few seconds. A flashing blue light on the newer models usually means a lockout; our guide on a Worcester boiler flashing blue light explains the patterns.
• Vaillant: ecoTEC boilers have a reset button on the control panel. The two lockouts you are most likely to see are Vaillant F28, a failure to ignite, and Vaillant F29, where the flame lit and then went out.
• Baxi: depending on the model there is either a reset button or a reset position on the mode dial that you turn to and hold briefly. Baxi E133 is the ignition failure code on many of their combis.
• Ideal: Logic and Vogue boilers reset from a button or by turning the mode knob to the reset position. Ideal L2 is the ignition lockout, and it is the one that most often appears after a power cut or an interruption to the gas.

Why a boiler keeps needing a reset

One lockout after a power cut or a cold night is normal. A boiler that needs resetting every day, or every time the heating comes on, has a real fault. These are the usual causes.

• Ignition faults. A worn ignition electrode, a flame sensing problem or a failing gas valve means the boiler cannot reliably light or cannot tell that it has.
• A frozen condensate pipe. On a condensing boiler in a hard frost, the plastic pipe that carries condensate outside can freeze and block. The boiler locks out, often with a gurgling noise. Pouring warm, not boiling, water along the outside section usually thaws it, and the boiler can then be reset.
• Overheating. Poor circulation, a sticking pump, sludge in a heat exchanger or a closed valve can let the water inside the boiler get too hot, which trips an overheat cut out.
• Flue or fan problems. If the fan cannot clear the flue properly, the boiler will not run. Birds nests and blocked terminals turn up more often in autumn than people expect.
• Pressure dropping. A sealed system that keeps losing pressure will keep stopping. Topping it up treats the symptom; the leak or the failed pressure relief valve is the fault. The opposite problem, boiler pressure too high, can also make the relief valve discharge and the pressure then fall.

Is it safe to keep resetting a boiler?

Pressing reset once or twice is what the button is there for. Pressing it ten times a day for a fortnight is not. Every failed ignition means gas has been released and not lit, which the boiler then has to purge. Components under repeated stress fail faster, and a fault that started small can turn into a bigger repair.

There is also a practical problem. A boiler that is limping along on regular resets usually gives up entirely on the coldest morning of the year, when every engineer in London is busiest. If yours has needed resetting more than a handful of times this autumn, it is worth having it looked at before the weather turns.

When to stop and call an engineer

A boiler diagnosis visit finds out why the boiler is locking out rather than guessing at a part. Call us on 020 4652 5111 or send an enquiry with the make, the model and the code on the display, and we will tell you what we think is going on before anyone comes out. We have 20 engineers across London, and our rate is on the pricing page, agreed before we attend. Any engineer who works on the gas side of your boiler must be on the Gas Safe Register, so ask to see their card. If you are weighing up whether to ring your usual plumber, the answer to can a plumber fix a boiler depends on which side of the casing the fault sits.

If the boiler heats your hot water through a cylinder, you can usually still get hot water while you wait by switching on the immersion heater. Our guide on how to get hot water without a boiler covers the other options.

• It locks out again after two attempts.
• The same fault code keeps coming back over days or weeks.
• The boiler makes a bang, a loud whoosh or a rumbling noise when it lights.
• You see scorch marks, soot or a yellow flame.
• There is water dripping from the boiler or from the pipes under it.
• The display is showing a code you cannot find in the manual.