Makes we repair
Why a boiler is not firing up
A boiler not firing up has either not been asked to light, or tried to light and couldn't. When nothing at all happens, the boiler may have no power, or the timer and the thermostat may not be calling for heat. Vaillant's advice names a home already at the thermostat's temperature as the most common reason a boiler doesn't fire.
When the boiler tries and then stops, it has locked out. The boiler found no flame after its tries to light, stopped for safety, and shows a code or a light. The makers' guides name these among the causes a householder can check:
- the gas supply
- a prepayment meter out of credit
- a frozen condensate pipe, in a frost
The parts that light and watch the flame are an engineer's. Ring us at any point, and we'll ask what the boiler is doing and what the display shows. Every boiler fault code, make by make. When the taps run cold, and what to check. Every boiler problem, and what each usually means.
Sources: Vaillant's and Glow-worm's advice on a boiler that won't ignite, and the makers' user guides.
The other causes
The other causes of a boiler that won't fire up are the ones below, as the makers' guides describe them. The makers don't rank them by how often they happen, so the order here isn't a league table.
Sources: the user guides and manuals of Vaillant, Ideal, Baxi, Worcester Bosch and Alpha, the advice pages of Vaillant, Glow-worm and Baxi, and Viessmann's advice on resetting a boiler.
What you can safely check
The safe checks for a boiler that won't fire up are the ones the makers' own guides give a householder. Never take the boiler's case off, and never touch anything that carries gas.
1. Is the power on?
The power comes first. Is the boiler's display lit? Check that the switch beside the boiler is on, and look at your fuse box for a tripped switch. A blank display with the power on can mean a failed part, which needs an engineer.
2. Are the controls calling for heat?
The timer and the thermostat decide when the boiler fires. Check that the timer is on and the heating is switched on. The room thermostat should be set above the room's temperature. A wireless thermostat with low batteries, or too far from its receiver, can't call the boiler on.
3. Is the gas on?
The gas supply is the next check. Try the hob or another gas appliance. If nothing gas works, check that the gas is on at the meter. On a prepayment meter, see that there is credit, and once it is topped up, reset the boiler. The current Vaillant ecoTEC plus and Ideal's guides also ask you to check the gas tap under the boiler hasn't been turned off. If you smell gas, don't touch anything. Open the gold "Smell gas?" bar on this page.
4. Is the pressure in range?
The pressure gauge should read about 1 to 1.5 bar with the boiler cold, on most makes. Glow-worm says a boiler below 1 bar may fail to light. Top it up as your user guide shows. If the pressure keeps dropping, the boiler needs an engineer. The F22 fault code page, for topping up the pressure.
5. Is it freezing outside?
The condensate pipe is the check in a frost. The section below shows how to find it and thaw it safely, at ground level.
If these checks don't bring the boiler back, stop there. Ring us and say what the boiler is doing.
Sources: the user guides and advice pages of Vaillant, Glow-worm, Ideal and Baxi.
A frozen condensate pipe and how to thaw it
A frozen condensate pipe stops a condensing boiler in a hard frost. The pipe carries the boiler's waste water to a drain, up to about 2 litres an hour, Worcester Bosch says. Where the pipe runs outside, the water can freeze in it, and the boiler then shuts down. The makers' own guides show a householder how to thaw it, where the pipe is at ground level and easy to reach.
1. Find the frozen part
The condensate pipe is usually white plastic, like a waste pipe, running from the boiler to a drain outside. The freeze is likeliest where the pipe is most exposed, at its end or at a bend or a dip. Look at the end for ice or debris, if it is safe to.
2. Warm it, at ground level
The frozen part thaws with any of these:
- a hot water bottle
- a microwavable heat pack
- a cloth soaked in warm water
- warm water poured along the pipe, never boiling
Do it where the pipe is at ground level and you feel able. Never climb to reach a pipe that runs high up a wall. Ring us instead. Mind your footing, as the water can freeze on the ground.
3. Restart the boiler
The boiler restarts once the pipe is clear. Reset it the way its user guide shows. If the boiler still won't fire, Baxi and Ideal say to call a Gas Safe registered engineer, so ring us. Lagging the pipe afterwards with weatherproof insulation makes another freeze less likely.
Sources: Worcester Bosch's leaflet on frozen condensate pipes and its user guides, Baxi's and Vaillant's advice on condensate pipes, Glow-worm's advice, and Ideal's Logic+ user guide.
Worth knowing
In a long cold spell, two makers suggest ways to make a freeze less likely. Worcester Bosch suggests turning the heating temperature on the front of the boiler up to maximum. Ideal suggests leaving the heating on all the time, with the room thermostat at 15 degrees overnight.
How to reset a boiler, once
Resetting a boiler is the last of the checks, done once, after the cause is put right. A reset clears the lockout and lets the boiler try to light again. Viessmann's advice says to put right whatever caused the lockout first. Otherwise you'll keep having to reset, and risk damaging the boiler.
The reset control depends on the boiler. It can be a button, a key under the display, or a dial turned to R. Some boilers reset like this:
- A Vaillant ecoTEC plus from before 2023: press the reset key for a second.
- The current Vaillant ecoTEC plus: hold the reset key for more than three seconds, as a shorter press puts it on standby.
- A Baxi or Potterton with a selector: turn it to Reset and hold it there for at least 5 seconds.
- An Ideal: press its Restart button or key.
Your user guide gives the steps for your model. The boiler may take a few minutes to run through its restart.
Resetting again won't fix a cause that is still there, so if the boiler locks out again, stop and ring us. The makers set limits too:
- Vaillant and Glow-worm: three resets at most, or five on a Glow-worm Compact.
- Ideal: five restarts in 15 minutes bring up Too Many Restarts.
- Worcester Bosch: its current boilers can go into a super lock-out, 2980, when five locking faults are reset in 15 minutes. A super lock-out needs an engineer.
- Alpha: the boiler shows E08 after five resets.
Sources: Viessmann's and Baxi's advice on resetting a boiler, and the user guides and manuals of Vaillant, Glow-worm, Ideal, Worcester Bosch and Alpha.
When to stop and ring an engineer
An engineer is the next step once one reset hasn't brought the boiler back, or as soon as you see any of these:
- The boiler won't light, yet the power is on and the controls are calling for heat. The gas works everywhere else in the home, and the condensate pipe isn't frozen.
- The boiler locks out again after a reset, or the same code keeps coming back.
- The condensate pipe is thawed, yet the boiler won't restart.
- The condensate pipe is frozen high up a wall, out of safe reach.
- The display is blank with the power on.
- The pilot light on an older boiler keeps going out while your other gas appliances work.
- You'd need to open the boiler to go further.
If you smell gas, don't reset anything. Open the gold "Smell gas?" bar on this page for the free emergency number. Gas safety at home, and what to do about a gas smell. Otherwise, ring us. Finding why a boiler won't fire is our Gas Safe registered engineers' job. What a repair visit involves, from the first checks to the fix.
Sources: the user guides and advice pages of Baxi, Ideal, Worcester Bosch and Vaillant.
What changes the price of the fix?
The cost of fixing a boiler that won't fire up depends on its cause. A frozen condensate pipe or a gas supply put right may need no part at all. But an ignition electrode, a flame-sensing electrode or a gas valve is a part to fit. The rate is agreed on the call, before an engineer comes, and no work is done until you say yes. How our rates work is set out in full.
Do you cover my part of London?
Yes: we fix boilers that won't fire up all over Greater London, day and night, in every borough north and south of the Thames. Pick your side of the river to see the areas.
North of the river
Every borough north of the Thames: Barnet and Enfield at the top, Hillingdon in the west, Havering in the east, and central London in between.
South of the river
Every borough south of the Thames: Richmond and Kingston in the west, Bexley in the east, and down through Croydon to Sutton and Bromley.
Questions about a boiler that won't fire
How many times can I reset the boiler?
Resetting the boiler once, after you've put the cause right, is the step to take. If the boiler locks out again, ring us. The makers' guides set limits beyond that. A Vaillant or Glow-worm allows three resets at most, and on an Ideal, five restarts in 15 minutes bring up Too Many Restarts. Even so, resetting again won't fix a cause that is still there.
There's a code on the display: what is it telling me?
A code on the display names the fault the boiler has found. The same code can mean different things on different makes, so read the make and model first. We'll ask for both, and the code, when you ring. The fault code pages give the codes make by make, with what each means and what you can safely check. Every boiler fault code, make by make.
Is it an emergency?
A boiler that won't fire up is a reason to ring us now, day or night. You don't have to work out first whether it's an emergency. Say what the boiler is doing, and we decide with you how soon an engineer needs to come. If you smell gas, though, the first call is the free emergency number in the gold "Smell gas?" bar on this page. What counts as a boiler emergency, and why to ring either way.
How much does it cost to fix?
The cost of fixing a boiler that won't fire up depends on what caused it and the part it needs, if any. The rate is agreed on the call, before an engineer comes. How our rates work is set out in full.
Don't know what has failed? You don't have to.Ring and say what you can see or hear. Finding the fault is our job.
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A real person answers and gives you the rate on the call. No work starts until you say yes, and repairs are guaranteed for 12 months: parts, labour and any return visit.
