Boiler stopped working in the cold? What to check tonight, and who has to fix it

Start with the simple causes

Smell gas, or a carbon monoxide alarm sounding? Go straight to the gas and carbon monoxide steps below. Otherwise start simple: Worcester Bosch's Greenstar 4000 manual notes that no appliance fault is found on over 30% of service calls.

Power. A gas boiler needs electricity. If its display is blank, check for a local power cut on our power cut tracker or by calling 105, which is free in England, Scotland and Wales (in Northern Ireland, NIE Networks is on 03457 643 643). If the house has power, check the boiler's own switch, the wall switch that feeds it (often a fused spur) and its circuit breaker in the consumer unit. If a breaker goes straight back to off, Citizens Advice says leave it and ask a registered electrician to look.

Settings. Citizens Advice suggests checking that the heating is not set to off or 'summer' mode, the clock shows the right time, the timer is in an on period, and the room thermostat is set above the room's temperature, or the heating will not come on.

Hot water only? On a combi, Citizens Advice suggests running the hot tap for a minute and setting the hot water to at least 50°C; with a cylinder, an immersion heater can stand in, though it can be expensive to run.

Check the pressure gauge

Many boilers stop if the water pressure in the heating system drops too low: Vaillant's ecoTEC plus and Baxi's 800 Combi manuals both say the boiler stops working below 0.5 bar. Citizens Advice says the gauge is usually a round dial on the front of the boiler or near the pipes beneath it; some boilers show the pressure on the display instead.

What counts as normal depends on the model. Baxi's 800 Combi manual recommends 1 to 1.5 bar when the boiler is cold, and Worcester Bosch's Greenstar 4000 manual checks for the same range, which is also the level Citizens Advice says to top up to; Vaillant's ecoTEC plus manual accepts anything from 1 to 2 bar when cold. Your own manual has the final word.

If it is low, top it up through the filling loop only as your own manual describes. If it does not show you how, or you cannot find the filling loop, leave it for an engineer: Baxi's manual says to ask your installer. Citizens Advice's checklist: heating off and the boiler cool, stop between 1 and 1.5 bar, and close the valves properly afterwards. Worcester Bosch says a system usually needs topping up once or twice a year; Baxi's manual says needing to do it regularly points to a fault or leak, so ask your installer or a Gas Safe registered engineer to find it.

Gas, meter credit and the condensate pipe

Power and pressure but no flame? Check whether another gas appliance, such as the hob, works: if not, Ideal's Logic Combi troubleshooting guide says to check the gas is turned on at the meter. If it was turned off because of a gas leak, leave it off: the Gas Safe Register says not to turn the supply on again until a Gas Safe registered engineer has checked it. If you do not know why it is off, ask one before turning it back on.

On a prepayment meter, check the credit: Ofgem says that once it runs out you cannot use any energy until you top up. If you cannot top up tonight, Citizens Advice says your supplier should give you temporary credit, and Ofgem says suppliers must offer help, such as extra credit if you are in a vulnerable situation. You pay it back when you next top up, and Ofgem says your supplier must work with you on a payment plan you can afford.

On oil, check the tank has not run dry. If the cold taps have stopped too, a combi has no mains water to heat (Worcester Bosch's basic checks include whether the cold water main is on): see frozen and burst pipes or no water supply.

In freezing weather, suspect the condensate pipe, the plastic pipe that drains waste water from a condensing boiler, which may run outdoors. Worcester Bosch's manual says a frozen or blocked condensate pipe will shut the boiler down, and to thaw one only if it is at ground level and easy to reach. Citizens Advice lists the signs: a fault code, gurgling or dripping water. Our frozen condensate pipe guide shows how to thaw it with warm, never boiling, water.

Fault codes, resets and when to call a Gas Safe engineer

Look up any display code in your manual (makers publish them online). Vaillant advises dealing with the cause first, such as low pressure or a frozen condensate pipe, and checking your manual for how to reset your model. Some faults are not for the user to reset: Baxi's 800 Combi manual marks those with a spanner symbol. Vaillant says a restart can take several minutes or a second attempt.

Stop if it will not restart, the code comes back or it keeps locking out. Beyond very minor fixes (thawing the condensate pipe, bleeding radiators, topping up the pressure), Vaillant says errors should be looked at by a Gas Safe registered engineer; for an oil boiler, nidirect advises an OFTEC registered technician. Never take the casing off: Worcester Bosch's manual says only a competent engineer can remove it. The law says no one may work on a gas fitting unless they are competent to do so, and the HSE says anyone employed to work on gas appliances in a home must be Gas Safe registered. If in doubt, switch it off and leave it off: the HSE says it is illegal to use a gas appliance you suspect is unsafe, and not to touch it until a Gas Safe registered engineer has checked it.

Registered engineers carry a Gas Safe ID card, with the work they are qualified to do listed on the back; check the licence number on the Gas Safe Register website or on 0800 408 5500. Still under the manufacturer's guarantee? Ring the maker first: Worcester Bosch's manual says it will not accept invoices for repairs by any other firm.

If you smell gas

Follow the National Gas steps: do not smoke or light matches, do not turn electrical switches on or off, open doors and windows, turn off the meter at the control handle unless the meter is in the cellar, and call the National Gas Emergency Service on 0800 111 999, free and 24 hours a day. The Gas Safe Register makes the same exception for a meter in a basement, and boiler manuals add: warn others, leave, and call from well away from the building. In Northern Ireland, call the NI Gas Emergency Service on 0800 002 001. For LPG, the Gas Safe Register says to call the number on the bulk tank or meter.

Carbon monoxide has no smell, and it can make you seriously ill. If a CO alarm sounds, or people at home have headaches, dizziness or sickness that ease outdoors, National Gas says stop using all appliances and switch them off, open doors and windows, get everyone out, call 0800 111 999 and do not go back in until the emergency services advise you. In Northern Ireland, call the NI Gas Emergency Service on 0800 002 001. Get medical advice as soon as possible: the NHS says call 999 or go to A&E if someone who may have been exposed is finding it hard to breathe, has suddenly become confused, has lost consciousness, is feeling weak or has chest or muscle pain, and not to drive yourself there; call NHS 111 if you think you might have symptoms.

Keeping warm, and safe, until it is fixed

The NHS advises heating the rooms you use to at least 18°C if you can, especially if you have a health condition. Until the boiler is back, Citizens Advice suggests layers (socks and slippers especially), hot water bottles, heated throws or electric blankets, a hot meal at least once a day, gentle movement and a portable electric heater, though it can be expensive to run. Or ask to stay with family or friends. More in our guide to staying warm without heating.

Rule out one shortcut: outdoor equipment indoors. The NHS says never use a barbecue or camping stove indoors, and Northern Ireland's Health and Safety Executive says only equipment designed to be used indoors should be brought inside the home, so the patio heater stays outside. Check your carbon monoxide alarm works, and know the symptoms of carbon monoxide poisoning.

If you rent in England

The repair is normally your landlord's job. For most tenancies, section 11 of the Landlord and Tenant Act 1985 requires landlords to keep the installations for space heating and heating water in repair and proper working order, and section 9A of the same Act, added by the Homes (Fitness for Human Habitation) Act 2018, requires the home to stay fit for human habitation. Tell your landlord or agent at once, in writing (GOV.UK says a text or email counts), and keep a copy. Do not attempt the repair yourself, and keep paying rent: GOV.UK warns that withholding it could make you vulnerable to eviction.

GOV.UK's How to rent a safe home guidance says landlords are generally allowed 'a reasonable period of time' to put a problem right once they know about it, and adds: 'With something serious or dangerous, like a boiler failure, or electricity outage, it might be reasonable to expect the landlord to arrange for a technician to attend within 24 hours to carry out an initial inspection.' Shelter says a broken boiler should be fixed more quickly in winter, and if the repair will take time you can ask for electric heaters or electric blankets. If a Gas Safe engineer has disconnected the boiler as unsafe, the HSE tells landlords they must provide emergency heating while the work is arranged. If nothing happens, contact your council's environmental health team, which GOV.UK says must take action if it thinks the problems could harm you.

Council and housing association tenants have firmer rules. Under Awaab's Law, in force for social housing since 27 October 2025, social landlords must investigate emergency hazards and make the home safe within 24 hours, and government guidance lists broken boilers among the hazards that could be emergencies, noting they are likely to be more serious in colder months. If the home cannot be made safe in time, the landlord must offer you somewhere else to stay. Complaints go to the landlord first, then the Housing Ombudsman. Awaab's Law does not yet cover private renting: the government says it will extend it to private landlords, with the timing subject to consultation.

If you rent in Scotland, Wales or Northern Ireland

In Scotland, private landlords must meet the Repairing Standard, which covers installations for space heating by a fixed heating system and for heating water, and must complete repairs within a reasonable time of being told (Housing (Scotland) Act 2006). Shelter Scotland says that if you are left without heating or hot water in cold weather, it could be reasonable to ask for a fix within one working day, and to keep paying your rent as normal. If nothing happens, you can apply free to the First-tier Tribunal for Scotland. Council and housing association tenants with no other heating usually have a Right to Repair within one working day, and could get compensation if it is missed.

In Wales, the Renting Homes (Wales) Act 2016 requires landlords to keep the home fit for human habitation and its heating and hot water installations in repair and proper working order, doing the work within a reasonable time of finding out. Welsh Government guidance gives a broken boiler as an example of an urgent repair, and warns that withholding rent can leave you in arrears and facing possession proceedings. Shelter Cymru says the council's environmental health team can look into serious repair problems that affect your health.

In Northern Ireland, nidirect says that where the tenancy terms are not clear, a private landlord is responsible for any installations for space heating and water heating; Advice NI and Housing Rights can help if there is a dispute.

Extra help, cover and what it might cost

In Great Britain, if anyone at home has reached State Pension age, is disabled, has a long-term health condition or has young children, join the free Priority Services Register with your energy supplier and network operator; Ofgem says it includes priority support in an emergency and help reconnecting your gas supply. Worried about an older relative or neighbour? The NHS suggests contacting the local council or the Age UK helpline on 0800 678 1602 (8am to 7pm every day), and NHS 111 if you think someone may have hypothermia.

Before paying anyone, check for cover you already have: Citizens Advice lists home emergency or boiler cover (sometimes bought with home insurance), packaged bank accounts, workplace benefits and the boiler's guarantee. The Financial Ombudsman says home emergency insurers normally pay for a tradesperson, parts and call-out charges, that most policies have an excess, and that the repair may be temporary. Ring the insurer first: the Ombudsman says most policies will not pay for a tradesperson you booked yourself.

Costs vary with each firm's charges, the fault and the parts, so Citizens Advice suggests getting a few quotes and asking whether there is a charge for coming out. If an insurer rules a boiler beyond economic repair, the Ombudsman says most home emergency policies offer a cash settlement of around £250 to £500 towards a new one. Whether cover is worth having is a separate question: see our boiler cover guide.