Boiler not firing up? What to check, and when to stop
A boiler that will not fire up is either not being asked to, or trying and failing. The first is usually the timer, the thermostat, the power or the pressure, and you can check all of those safely. The second shows as clicking, a lockout code or both, and after one reset it is a job for a Gas Safe registered engineer. Request a repair callback, or call 0333 772 6247 (lines open Monday to Friday, 08:00 to 18:00; one-off repair visits run Monday to Friday, 09:00 to 17:00). If you can smell gas, ring 0800 111 999 first.
Smell gas? Stop here
If you can smell gas, hear hissing at the gas pipework or the meter, or your carbon monoxide alarm is sounding, do not run any of the checks on this page. Do not touch electrical switches. Put out any naked flames, open the doors and windows, turn the gas off at the meter control valve if you can do so safely, leave the property and call the National Gas Emergency Service on 0800 111 999.
A boiler that simply will not light, with no smell of gas and no carbon monoxide alarm sounding, is not a gas emergency. It is the boiler protecting itself, and the rest of this page is for that situation.
Boiler won't ignite, or not being asked to?
Stand by the boiler for a minute with the heating turned up. What it does next tells you which half of this page you need.
If nothing happens at all, with no clicking, no fan and no code, the boiler usually is not getting a call for heat, or has no power. That points at the controls: the timer, the thermostat, a boiler left on hot water only after the summer, or the switch that feeds it. These are the checks you can safely make yourself.
If you hear a run of fast clicks but never the soft whoosh of the burner catching, or a fault code appears on the display, the boiler is trying to light and not managing it. After a set number of failed attempts it locks out, which is a safety shutdown rather than a breakdown in itself. The usual causes are an interrupted gas supply, a frozen condensate pipe in cold weather, low system pressure, or a worn part on the gas side, and only the first three are anything you can look at.
What you see, and what it usually means
| What the boiler does | Most likely cause | Who deals with it |
|---|---|---|
| Nothing at all: blank display, no sound | No power reaching the boiler, such as its switch turned off | You can check the fused spur switch is on. If it is on and the display stays blank, book an engineer. |
| Display on, no code, no sound | No call for heat: the timer is off, the thermostat is set below the room temperature, or the boiler is on hot water only | You. Work through the controls in the checklist below. |
| Fires for a hot tap but not for the heating | The boiler can light, so the fault is in the heating side: the controls, or a stuck diverter or motorised valve | Check the controls first. A valve fault is engineer work. See our hot water but no heating guide. |
| Pressure gauge below about 1 bar, often with a code | Too little water in the sealed system for the boiler to run safely | You can top up using the filling loop as your manual shows. If it drops again, book an engineer. |
| Gurgling in cold weather, then a lockout code | A frozen condensate pipe outside | You can thaw it from ground level, as your boiler manual or manufacturer advises. If it refreezes or will not clear, book an engineer. |
| Clicking with no flame, then a lockout code | The burner is not lighting or the flame is not being sensed: gas supply, ignition or flame-sensing electrode, or gas valve | Check your other gas appliances and reset once. After that, a Gas Safe registered engineer only. |
Safe checks, in the order to do them
Every one of these happens outside the boiler casing. None of them involves the gas side of the boiler, so they are all safe for a homeowner.
- Look at the display. If it is blank, check the switch that feeds the boiler (usually a switched fused spur on the wall nearby) is on. Do not open or rewire anything. If it is on and the display is still blank, book an engineer.
- Check the timer or programmer is calling for heat now. After the clocks change, a mechanical timer can be an hour out, so the heating may simply be off at the time you expect it on.
- Turn the room thermostat up above the current room temperature, to about 21°C. If it is wireless, check its batteries and that it is still paired to the boiler.
- Check the boiler is not set to hot water only, a setting often left on after the summer.
- On a combi, run a hot tap. If the boiler fires for hot water, it can light, and the problem is on the heating side rather than the burner.
- Read the pressure gauge with the system cold. Most boilers want about 1 to 1.5 bar when cold, but check your own manual for your boiler's figure. Below that, top up using the filling loop exactly as your boiler manual shows.
- Check your other gas appliances, such as the hob. If they will not light either, the problem is the gas supply, not the boiler. On a prepayment meter, check there is credit.
- In freezing weather, find the plastic condensate pipe where it leaves the house. If it is frozen, thaw it with a hot water bottle, a heat pack or a cloth soaked in hot water, never boiling water, and only if you can reach it from the ground. Follow your boiler manual or manufacturer's advice on this.
- Write down any fault code exactly as it appears, then reset the boiler once, following the reset step in your manual. If the code comes back, stop there.
Why one reset, and only one
A reset clears the lockout. It does not fix whatever caused it. If a thawed condensate pipe or a restored gas supply was the problem, one reset brings the boiler back and it stays back. If the code returns within minutes or hours, the boiler is telling you something is genuinely wrong, and pressing reset again only hides it.
Some boilers also add a lockout of their own after too many resets in a short time. One reset, then book an engineer.
Clicking, then a fault code?
If the boiler clicks, then shows a fault code and stops, that is an ignition lockout. Our boiler ignition lockout guide explains the codes by brand, and the links at the foot of this page go to the guide for each code.
Whatever the brand, the parts behind these codes are the ignition and flame-sensing electrodes, the gas valve and the control board. All of them sit inside the casing, and all of them are Gas Safe registered engineer work. HSE states that anyone employed to work on gas appliances in domestic premises must be a Gas Safe registered engineer.
When to stop and book an engineer
Book an engineer if the checks above are all fine and the boiler still will not fire, if a lockout code returns after one reset, if the pressure will not hold after a top-up, if the condensate pipe keeps refreezing, or if your gas appliances work but the boiler clicks without lighting.
You can book a one-off repair without joining a plan. Request a repair callback, or call us on 0333 772 6247, and we will arrange a Gas Safe registered engineer to attend and diagnose the fault. One-off repair visits run Monday to Friday, 09:00 to 17:00. A £95 call-out fee applies and is paid in advance, and the engineer tells you what is needed before any further work goes ahead. One-off repairs do not carry a workmanship guarantee.
Boiler not firing up: FAQs
Why is my boiler not firing up?
Either it is not being asked to, or it is trying and failing. If nothing happens at all, check the power, the timer, the thermostat and that the boiler is not on hot water only. If it clicks, shows a code or locks out, the usual causes are the gas supply, a frozen condensate pipe, low pressure or a worn ignition part. Check your gas appliances, thaw the condensate pipe if it is frozen, reset once, and book a Gas Safe registered engineer if the code returns.
Why is my boiler clicking but not igniting?
The clicking is the spark trying to light the burner. If the burner never catches, the boiler is not getting gas, or the flame is not being sensed. Check that your hob or other gas appliances work and that a prepayment meter has credit. If they do, reset once. If it clicks and locks out again, the ignition electrode, the flame sensor or the gas valve may need a Gas Safe registered engineer.
Is a boiler that will not fire up dangerous?
On its own, no. A lockout is the boiler shutting down safely because it could not confirm a flame. It becomes an emergency if you can smell gas, hear hissing at the gas pipework or meter, or your carbon monoxide alarm sounds. In that case leave the checks, get out and call the National Gas Emergency Service on 0800 111 999.
Can low boiler pressure stop a boiler firing up?
Yes. When the pressure in a sealed system falls below the minimum the boiler needs, it shuts down and shows a code rather than firing with too little water. Most boilers want about 1 to 1.5 bar when cold, but check your own manual for your boiler's figure. Top up using the filling loop as your manual shows. If the pressure drops again within days, there may be a leak, which needs an engineer.
My boiler fires for hot water but not for the heating. What is wrong?
Then the burner can light and the fault is on the heating side. See our hot water but no heating guide for the checks.
How many times should I reset my boiler?
Once, following the reset step in your boiler manual. If the code comes back, stop. Repeated resets do not fix the cause, and on some boilers they trigger a lockout of their own.
Will a Smart Plan cover plan pay if my boiler has already stopped firing?
Probably not for this fault, and it is better to know that now. For the first 30 days of a plan, any call-out carries the £95 call-out fee, paid in advance, although cover still applies. If the engineer finds a defect, we quote to put it right, and until the defect is remedied the terms class that part of the equipment as an exclusion. Work where the cause is freezing, such as a frozen condensate pipe, is also excluded, and so are resetting the boiler, adjusting settings, replacing batteries and repressurising the system. A call-out that turns out to need only one of those carries the £95 call-out fee. So a boiler that has already stopped is usually a one-off repair. Request a callback and ask about cover for the next fault at the same time.
Book a repair now, then cover the next breakdown
Cover is for the breakdown that has not happened yet, so a boiler that has already stopped usually needs a one-off repair first. On the boiler and central heating module, cover pays parts and labour on the equipment listed on your cover sheet, up to £500 in each 12-month period if your boiler is under 7 years old, or up to £200 if it is over 7. Work caused by freezing or frost damage, work caused by a loss of gas or electricity supply, and work caused by sludge, scale deposits, rust or corrosion, are excluded. So are resetting the boiler, adjusting settings, replacing batteries and repressurising the system, so a call-out that turns out to need only one of those carries the £95 call-out fee. When something covered breaks, we aim to get an engineer out to you within two working days, inside our cover-plan call-out hours of Monday to Friday, 08:00 to 18:00, through a national network of thousands of Gas Safe registered engineers we work with. A £95 call-out fee, paid in advance, applies in your first 30 days, on faults the plan does not cover, and on no-access visits, and your cover still applies throughout those first 30 days. Using a service starts a 12-month agreement period. Smart Plan is a service plan, not insurance, from UK Boiler Company Ltd, trading since 2014.
Helpful links
- No heating? Book a one-off repair
- Boiler repair as a one-off job
- Boiler ignition lockout explained
- Hot water but no heating
- What should boiler pressure be?
- Boiler losing pressure
- Heating timer wrong after the clocks change
- Faulty diverter valve symptoms
- Worcester Bosch EA / 227: no flame detected
- Ideal L2: flame loss or ignition lockout
- Vaillant F28: ignition lockout
- Baxi E133 fault code
- All boiler fault codes by brand
- Boiler and central heating cover
- HSE domestic gas safety FAQs
- Check an engineer on the Gas Safe Register
Call us today
Customer service
0333 772 6247New customers
0333 772 6247Write to us
By email
hello@smart-plan.comBy post
2nd Floor, Melrose House
42 Dingwall Road
Croydon
CR0 2NE