How to reset a boiler safely

Smell gas or hear a carbon monoxide alarm? Do this before anything else

Do not press reset, and do not try any of the checks on this page. A boiler that has shut down while gas is escaping must stay off.

Call the National Gas Emergency Service on 0800 111 999. The gas network SGN also says to open windows and doors, and to turn off the gas supply at the meter and any gas appliances. Do not smoke or use naked flames, and do not touch any electrical switches, because "Turning a switch on or off could ignite a gas leak." Do not go into a cellar, even if the meter is down there. Source: SGN, what to do if you smell gas.

If you suspect carbon monoxide, for example because your CO alarm has gone off, the Health and Safety Executive says to call 0800 111 999, switch off the appliance, shut off the gas at the meter control valve and open all doors and windows. If you have symptoms, it says to seek urgent medical advice from your GP or an A&E department. Source: HSE gas safety FAQs.

How to reset a boiler, step by step

Work through these in order, and stop at any step that tells you to. Nothing here involves opening the boiler: never take off the casing or front cover, because the parts inside are a Gas Safe registered engineer's job.

1. Write down what the boiler is showing: the code, or which light is on or flashing, and the make and model from the boiler's data badge. You need both to find the right method below, and any engineer will ask for them.

2. Check the boiler has power. If the display is completely blank, there is nothing for a reset button to restart. Go to our guide to no power to a boiler instead.

3. Check gas is reaching your home. Try another gas appliance, such as the hob. If the boiler is your only gas appliance, check whether the gas supply is on at the meter, as Ideal's Logic System guide says. If the gas is off at the meter and you do not know why, do not reset: contact your gas supplier or a Gas Safe registered engineer. If a prepayment meter has no credit, top up or contact your supplier. If your other gas appliances also fail and there is credit on the meter (or you have a credit meter), do not reset: call the Gas Emergency Service on 0800 111 999, as the gas network SGN advises for a loss of gas supply.

4. Look at the pressure gauge and compare it with the range in your boiler's user manual. If it is low, top up only in the way your manual describes. If the pressure will not rise, or you cannot find the filling loop or your manual, stop and book a Gas Safe registered engineer. Our guide to what boiler pressure should be explains the gauge.

5. Find the reset or restart control for your make (the brand sections below link to each maker's own instructions) and press it once, for as long as your maker says and no longer.

6. Give the boiler a few minutes. Vaillant says some boilers take several minutes to reset, and some may even need two attempts. This guide's safety rule is still one press: a second lockout means the safety fault is still there, so wait, do not press again, and if the boiler does not come back, go to the stop point below.

7. Stop point. If the boiler runs normally, you are done. If it locks out again or the same code returns, do not press reset a second time. Switch the heating off at the controls and book a Gas Safe registered engineer.

Where is the reset button on a boiler, and what symbol does it have?

It is on the front control panel, or behind a fold-down flap that is made to be opened by hand. That flap is as far as you go. What the control looks like depends on the maker, and the makers' own descriptions are:

Vaillant: on the boiler's display, and it "will likely show a flame with a line crossed through it" (Vaillant).

Baxi: a reset button, the temperature knob, or an ON/OFF/selector switch with an R (Reset) position, depending on the model (Baxi).

Ideal Logic System: a button labelled RESTART, not reset, so look for that word (Ideal).

Older Glow-worm Energysaver Combi: a Reset button on the control fascia, which you reach by lowering the drop-down panel on the front (Energysaver Combi 80/100 manual, PDF).

If you cannot see a control that matches, your boiler may use a dial or a menu instead. The section on boilers with no reset button covers that.

Reset button, power switch or gas top-up: which one you need

People often mix up three different actions. They do different jobs.

Reset or restart button: the maker's control for restarting the boiler after it has shut itself down for safety, usually with a code or a warning light showing. Press it once, as your manual says. This is the action the brand sections below cover.

Switching the power off and on: the boiler's fused spur switch, usually on the wall near the boiler, cuts and restores its electricity. It is not the maker's reset step, so do not use it in place of one unless your manual says to. Use it to check power when the display is blank, as set out in step 2 above. If the power to the boiler keeps tripping, see the power-cut section below.

Restart after a prepayment top-up: Vaillant says a boiler on a pay-as-you-go meter may shut down when the gas runs out, and you reset it once you have topped up. The checks to do first are in how to reset after a top-up.

How many times can you reset a boiler?

Once. That is this guide's safety rule. A boiler that stops and shows a code has shut itself down because one of its safety checks failed, for example it tried to light and saw no flame. A reset restarts the boiler, but it does not repair whatever made it shut down.

Baxi puts it this way: "If lockout occurs frequently a fault is indicated and you should contact your installer or service engineer." Vaillant says that if your boiler does not turn on after resetting, or the error code is still in place, contact a Gas Safe registered engineer. If your boiler tried to light and gave up, our guide to boiler ignition lockout explains what it is protecting you from.

What if my boiler has no reset button?

Many boilers have no separate button. Vaillant notes that some boilers use a reset dial instead and says to check the manual (Vaillant). On some Baxi boilers you turn the temperature knob fully anticlockwise, or turn the selector switch to R, as set out in the Baxi section below. Some Worcester Bosch panels reset through the display keys rather than a single button: our Worcester boiler control panel guide covers those.

On an older boiler with no manual to hand, look up the model on the maker's website, using the name on the front panel or data badge. Makers keep manuals for older models online, for example in Glow-worm's literature library. If the only way to reach a reset control is to remove a cover or panel, do not do it: that is a job for a Gas Safe registered engineer.

Worcester Bosch

Worcester Bosch reset steps differ from one model to the next, so check the user manual for your boiler on Worcester's boiler user manuals page. Our Worcester boiler control panel guide walks through the buttons and display for each panel. If a code comes back after one reset, look it up in our Worcester Bosch fault codes list and call a Gas Safe registered engineer.

Vaillant boiler reset

According to Vaillant's own reset guide, the reset button is on the display and usually shows a flame with a line through it. Vaillant says you only need to press it for three seconds, and its general steps say to hold a reset button for no more than 10 seconds.

For ignition faults, the same Vaillant page names blockages in the flue, a faulty gas valve and an issue with the ignition lead as the most common causes. All three sit in the flue or inside the casing, so a reset cannot fix them and they are a job for a Gas Safe registered engineer.

Look up the code on your display in our Vaillant boiler fault codes guide.

Baxi boiler reset

Baxi's own reset guide gives three methods, because different Baxi models have different controls. Use the one that matches your boiler:

Reset button: press it until the red light goes out. Baxi gives no fixed hold time for this one.

Temperature knob: turn it fully anticlockwise and hold it there until the red lockout light goes out, then turn it back to your usual setting.

ON/OFF/selector switch: turn it to the R (Reset) position, hold it for at least 5 seconds, then release.

Whichever control yours has, use it once. Baxi says "If lockout occurs frequently a fault is indicated", so if the lockout shows again (the red lockout light, or the flashing flame failure light on selector-switch models with neon lights), call a Gas Safe registered engineer.

To read the code first, see our Baxi boiler fault codes guide.

Ideal boiler reset

On the Ideal Logic System, the button is labelled RESTART rather than reset, which is easy to miss if you are scanning the panel for the word reset. Ideal's Logic System troubleshooting guide says that once you have topped the pressure up to 1 bar with the filling loop, you turn off the filling loop tap and press the boiler's RESTART button. For F2 (flame loss), Ideal says first check whether other gas appliances work, and on a prepayment meter whether there is credit. For L2 (ignition lockout), it says check the condensate pipe for blockages first, then the gas supply. If the code stays, contact Ideal if the boiler is under warranty, or a Gas Safe registered engineer. The guide gives no hold time, so a normal single press is all it asks for.

Other Ideal ranges may label or place the control differently, so check the user manual for your model before pressing anything.

Find your code in our Ideal boiler fault codes guide.

Glow-worm boiler reset

Glow-worm says "Often, resetting a boiler can resolve a fault or temporarily get your boiler working again", and says your user manual will help you reset your boiler. You can find yours on Glow-worm's manuals and literature page. Its fault codes page adds: "We strongly advise that you do not gain access inside your boiler as this can be dangerous."

On older models, wait before you press. Glow-worm's user manual for the older Energysaver Combi 80 and 100 says: "Allow the boiler to cool down for at least four minutes then press the Reset button" (Energysaver Combi 80/100 user manual, PDF). That wait is for that older range. For any other Glow-worm, follow your own manual.

Look up the code in our Glow-worm boiler fault codes guide. The word "temporarily" in Glow-worm's advice matters: if the fault returns after one reset, it is still there, so call a Gas Safe registered engineer.

How to reset a boiler after a power cut

While the power is off, a gas boiler cannot run. To check whether a power cut is affecting your area, the gas network SGN suggests powercut105.com.

Look at the display before you press anything. A boiler often restarts by itself: the older Glow-worm Energysaver manual, for example, says normal operation "should resume when the electrical supply is restored", and that if it does not, the boiler's safety cut-off may have operated and needs the reset button (Energysaver Combi 80/100 manual, PDF). So reset only if a code or warning light is showing once the power is back, and only once.

If the rest of the house has power but the boiler display stays blank, check the boiler's fused spur switch is on, then follow our no-power guide. Never open the consumer unit or touch any wiring. If the power to the boiler keeps tripping, call a registered electrician.

The same Glow-worm manual says to reset any external controls to resume normal operation of the central heating.

How to reset a boiler after the gas runs out or a prepayment top-up

Top up the meter first. Vaillant says that on a pay-as-you-go meter the boiler may have shut down because you ran out of gas, that you reset it once you have topped up, and that "In most cases, emergency gas can be added to your meter if necessary."

Before you reset, run the gas check in step 3.

If you smell gas when the supply comes back, do not reset: call the National Gas Emergency Service on 0800 111 999, as the HSE gas safety FAQs set out.

What a reset can fix, and what it cannot

A reset can help with

A one-off stop with no obvious cause. Glow-worm's wording is that a reset "can resolve a fault or temporarily get your boiler working again" (Glow-worm). Next step: press once, then keep an eye on it over the next few days.

Gas that ran out on a prepayment meter, once you have topped up (Vaillant). Next step: check the hob lights, then reset once.

Low pressure, where the manual says to press reset or restart after topping up. Ideal's Logic System guide is one example (Ideal). Next step: top up only as your manual says, then reset once.

A reset will not fix

A shutdown that keeps happening. Baxi says frequent lockout is a sign of a fault (Baxi). Next step: stop and book a Gas Safe registered engineer.

An ignition fault from a cause inside the boiler or flue (see the Vaillant section). Next step: a Gas Safe registered engineer only.

A blank display. With no power there is nothing to reset. Next step: go back to step 2.

Pressure that drops again after a top-up. That points to water leaving the system. Next step: read why a boiler keeps losing pressure and book an engineer rather than topping up again and again.

A gas smell or a carbon monoxide alarm. Never reset. Next step: call 0800 111 999 and follow the steps at the top of this page.

Why won't my boiler come back on after a reset?

Because the reason it stopped is still there. A reset only restarts the boiler's safety checks. If the gas is reaching the boiler, the display has power and the pressure matches your manual, but the boiler still will not run or the code returns, the cause is inside the boiler or on the gas side. Do not press reset again, and never open the casing. Book a Gas Safe registered engineer.

In freezing weather, a frozen condensate pipe (the plastic pipe that carries water from the boiler to a drain) can also stop a condensing boiler. The older Glow-worm Energysaver manual, for example, says the boiler stops as a safety feature if the condensate drain is blocked, and that ice in the pipe outside the house may be the cause (Energysaver Combi 80/100 manual, PDF). Vaillant counts defrosting condensate pipes among the very minor fixes a homeowner can do (Vaillant). Glow-worm's Energysaver Combi 80/100 manual says to release an ice blockage with warm cloths on the pipe, then press reset. Check your own manual for your model. Press reset once, and book an engineer if the fault persists.

Before you call an engineer, have four things ready: the make and model from the data badge, the code or light pattern, what happened just before the boiler stopped (a power cut, the gas running out, a pressure drop, or nothing obvious), and whether your other gas appliances work.

You can check an engineer on the Gas Safe Register before they start work. If your boiler will not light at all, our guide to a boiler not firing up goes through the likely causes.

Will a cover plan send an engineer just to reset the boiler?

Usually not for the reset on its own, and it is better to know that before you book. The general exclusions in section 10 of Smart Plan's cover plan terms (page 26) apply to every product. Exclusion 10.1 leaves out "Any works involving adjustments to settings, replacement of batteries and resetting of equipment", and exclusion 10.2 leaves out "Repressuring of any equipment". So a visit only to press reset or top up the pressure may not be covered.

Section 10 also leaves out works caused by a loss of, or reduced, supply of gas or electricity to the property (exclusion 10.19, page 27), and works where the cause of the issue is freezing (exclusion 10.21, page 27). So a boiler that stopped because the power went off, the meter ran dry or the condensate pipe froze is not a covered breakdown in itself.

Cover is for the breakdown behind a fault that will not clear. Boiler cover repairs that breakdown up to the cover limit in section 2.1(d) (page 8), subject to the exclusions. Exclusion 10.13 (page 27) leaves out "Any works to repair a defect/s that we have identified on your equipment". Definition 14 says a defect includes a fault deemed to exist before the plan started, and general term 9.11 explains how one is identified and quoted for. If the PCB or heat exchanger has failed, the terms treat the boiler as beyond economic repair (section 2.1(c), page 8). In that case the plan pays a contribution worked out under general term 9.5 (page 23) instead of a repair.

A £95 call-out fee may apply, only in the situations set out in the terms. One of those situations is a visit where the issue turns out to fall under an exclusion, such as a reset on its own (general term 9.2, page 23). Call-outs run Monday to Friday, 08:00 to 18:00, unless it's an emergency breakdown (section 9.17, page 25). Smart Plan is a home service plan from UK Boiler Company Ltd.

Cover the next breakdown: get a call back

A cover plan is not for pressing reset or topping up the pressure. Leave your number and we will call you back to talk through boiler and central heating cover for next time.

Helpful links

• Worcester Bosch fault codes
• Vaillant fault codes
• Baxi fault codes
• Ideal fault codes
• Glow-worm fault codes
• Boiler ignition lockout explained
• Worcester boiler control panel explained
• Boiler & central heating cover
• Vaillant: how to reset a boiler
• Baxi: how to reset a Baxi boiler
• SGN: what to do if you smell gas
• Check an engineer on the Gas Safe Register