Boiler Not Firing Up? Why Your Heating Won't Come On — and What to Check First
A boiler that will not fire up — the display is on, you turn the heating up, and nothing happens, or it clicks and gives up — is the most common heating breakdown in Britain, and it clusters heavily in the first cold weeks of autumn and every hard frost after that. The good news is that in most cases the boiler itself is fine: it is refusing to light because something it needs is missing. Gas, water pressure, a clear condensate pipe, a call for heat from the controls, and a reset after a lockout account for the overwhelming majority of 'boiler not firing up' calls, and every one of those is something you can check safely yourself in the next ten minutes. This guide walks through them in the order that finds the problem fastest, explains what the ignition fault code on your particular brand is telling you, and is clear about the point at which it becomes a Gas Safe engineer's job.
⚠️ This guide covers checks you can carry out safely from outside the boiler — gas supply, pressure, the condensate pipe, controls and the reset button. Never remove the boiler casing or attempt to work on the gas valve, electrode, fan or wiring: all work on a gas appliance must by law be carried out by a Gas Safe registered engineer (OFTEC for oil). If you smell gas, do not operate electrical switches, leave the property and call the National Gas Emergency line on 0800 111 999.
Quick answer: the five things that stop a boiler firing up
| Check | What you're looking for | Fix |
|---|---|---|
| 1. Fault code on the display | Any code — EA, F28, E133, L2, F1… | Look it up; it tells you which of the checks below applies (see the brand section) |
| 2. Gas supply | Does the hob light? Prepayment meter in credit? Meter valve open? | Restore the supply, then reset the boiler once |
| 3. Water pressure | Gauge below about 0.8–1 bar | Top up to 1–1.5 bar via the filling loop, then reset |
| 4. Condensate pipe (cold weather) | Plastic pipe outside, frozen; boiler gurgles then locks out | Thaw with warm water, then reset |
| 5. Controls calling for heat | Thermostat set above room temperature, programmer in an 'on' period, smart stat connected | Turn the stat up 5°C and listen for the boiler; check the app / batteries |
If all five are fine and the boiler still tries and fails to light, the fault is inside the boiler — usually the ignition electrode, the fan or flue, the gas valve or the control board — and that is where a Gas Safe registered engineer takes over.
First: is it 'not firing up' or 'not being asked to'?
These feel identical from the sofa but are different problems. A boiler that is not being asked for heat sits quietly with no fault code, the display showing standby or a temperature, and nothing happening when you turn the thermostat up. A boiler that is trying and failing to fire runs its fan, clicks (the ignition spark), sometimes lights briefly, then shows a fault code and locks out.
For the quiet-and-no-code case, look at the controls before the boiler: the room thermostat (turn it up well above room temperature and listen for a click), the programmer or timer (is it in an 'on' period, and has the clock drifted after a power cut?), and smart thermostats — a Hive, Nest or Tado that has lost its connection or has flat batteries in the receiver will leave a perfectly healthy boiler cold. See our guide to a thermostat not talking to the boiler.
For the tries-and-fails case, note the fault code exactly and carry on below.
Check 1: the gas supply
The single most common reason a gas boiler will not fire up is that there is no gas — and it is easy to miss because the boiler's display is electric and looks perfectly alive.
- Try the gas hob or a gas fire. If nothing lights, the boiler is not the problem.
- Prepayment meter: check the credit, and whether the emergency credit has been used. A smart prepay meter that has run out cuts supply silently.
- The emergency control valve next to the meter should be fully open — the handle in line with the pipe. They get knocked during building work and by things being stored against them.
- If the whole street is off, call the National Gas emergency line on 0800 111 999.
If you smell gas at any point, stop, do not operate switches, leave the property and call 0800 111 999.
Check 2: water pressure
A sealed heating system needs to be pressurised, and every modern boiler refuses to fire if the pressure gauge drops below about 0.5–0.8 bar. After a summer switched off, a small weep somewhere in the system has often let the pressure drift down, so the first cold morning the boiler simply will not start — usually with a pressure code: F22 on Vaillant and Glow-worm, E119 on Baxi and Potterton, F1 on Ideal, CE 207 on Worcester.
Top it up to 1–1.5 bar with the filling loop, with the heating off and the system cold, then reset. Our step-by-step guide to increasing boiler pressure covers every type of filling loop. If you are topping up more than a couple of times a year, something is losing water — see boiler losing pressure.
Check 3: the condensate pipe (the winter classic)
If the boiler worked yesterday, it is freezing outside, and this morning it gurgles, tries, and locks out with an ignition code — it is the condensate pipe until proven otherwise. Every condensing boiler drains a trickle of acidic water through a plastic pipe, and where that pipe runs outside a hard frost freezes it solid. The water backs up into the boiler, and the boiler's safety logic will not let the burner light.
Find the exposed white or grey plastic pipe outside, pour warm (never boiling) water along it or hold a hot-water bottle against the frozen section until you hear a trickle, then reset the boiler. It will fire straight away. Our frozen condensate pipe guide has the full procedure and the permanent fixes — lagging, re-routing, or a trace-heating cable — so it does not happen every cold snap.
Check 4: reset the boiler — once
After a lockout, most boilers will not retry on their own; they wait for a reset. That is deliberate. Press and hold the reset button (usually marked with a flame symbol, or a rotary control with a reset position on older boilers) for a few seconds and watch: the fan should spin up, you will hear a series of clicks as the electrode sparks, and the burner should light.
Do this once, after you have checked gas, pressure and the condensate pipe. If the boiler locks out again immediately, stop. Each reset is another attempt to admit gas and ignite it; repeated attempts against a real fault achieve nothing and can flood the combustion chamber. Our how to reset a boiler guide shows where the button is on each brand.
What the ignition fault code means on your brand
When the boiler tries and fails to light, the code it shows is the most useful thing on the display. Every major brand has a signature ignition-lockout code — note it exactly (including any sub-code) and follow the link for the full causes and fixes:
| Brand | Ignition / flame-loss code | Notes |
|---|---|---|
| Worcester Bosch | EA (EA 227 = never lit, EA 229 = lit then lost) | Greenstar 4000/8000 show a sub-code — record it |
| Vaillant | F.28 (won't light) / F.29 (lit then lost) | Also F.27 for a 'false flame' |
| Glow-worm | F28 / F29; older models F1 | Same electronics as Vaillant |
| Baxi | E133 | Older displays show 'E1' then '33' |
| Potterton / Main | E133 | Same platform as Baxi |
| Ideal | L2 (lockout after repeated F2) | Logic and Vogue ranges |
| Alpha | E1 | E-Tec, InTec |
| Viessmann | F4 / FD | Vitodens range |
| Ariston | 501 | Often preceded by 5P1/5P2 warnings |
On all of them the homeowner checks are the same — gas, pressure, condensate, one reset — and the internal causes are the same family: a worn ignition electrode, low gas pressure under load, a flue or fan problem, the gas valve, or the control board. If your brand is not listed, search it in our fault code finder.
Worcester boiler not firing up
The most-searched brand variant, simply because Worcester is the most installed. A Greenstar that will not fire shows EA — on the 4000, 8000 and CDi with a sub-code, most often EA 227. Worcester boilers are very frequently fitted on an outside wall with an external condensate run, so in a frost check the pipe before anything else. The blue-ring i and Si models have a simple display and a reset button on the front; the 4000 and 8000 have the reset on the fascia beneath the display. Low pressure shows as CE 207 and stops the boiler firing just as surely as an ignition fault.
Vaillant and Glow-worm boiler not firing up
Vaillant's ecoTEC and Glow-worm's Energy, Ultimate and Betacom share electronics and codes. Will not light at all: F.28. Lights then goes out: F.29. Low pressure: F.22. Vaillant limits the number of consecutive resets by design, so if the crossed-flame reset button seems to stop working, that is the boiler telling you the fault is real. F.75 — the pump/pressure-sensor fault — also stops these boilers firing and is not fixed by topping up.
Baxi, Potterton and Main boiler not firing up
All three share Baxi's control platform, so the code is E133 — shown as 'E1' alternating with '33' on older two-character displays. Gas supply first: these boilers are very common in rented and prepayment-meter homes, and an empty meter is the number one E133 cause. Low pressure shows as E119 (or E1 19). Reset is a button on newer models and a rotary selector with a reset position on the Duo-tec and older Platinum.
Ideal boiler not firing up
An Ideal Logic or Vogue that will not fire shows L2 — the flame-loss lockout — usually after flickering F2. It is the single most common Ideal complaint every winter and, on a Logic fitted with an external condensate pipe, it is a frozen pipe more often than anything else. Low pressure shows as F1. The reset is the flame-symbol button on the front.
Oil boiler not firing up
Oil boilers (Grant, Worcester Greenstar oil, Firebird, Warmflow) fail to fire for their own set of reasons: an empty or nearly empty tank (the pick-up sits above the sludge at the bottom, so a tank can read 10% and still starve the burner), a blocked oil filter, an airlock in the fuel line after running dry, waxed oil in extreme cold, or a burner lockout that needs the button on the burner itself pressing. Check the tank gauge and the burner's reset button (press once), then call an OFTEC-registered technician rather than a gas engineer — oil is a separate competence. Our Grant and Firebird code pages cover the specific lockout codes.
When it is time for a Gas Safe engineer
Once gas, pressure, condensate and controls are proven and a single reset has not cured it, the remaining causes all live inside the boiler: the ignition electrode and lead (the most common, and cheap), gas pressure under load, the fan and flue, the gas valve, and the control board. Every one of those requires the casing off and is legally Gas Safe registered work.
Call an engineer straight away rather than resetting repeatedly if: the boiler lights then goes out with a bang or a smell; the display shows a code you cannot clear; you smell gas (0800 111 999 first, then the engineer); or the pressure keeps dropping after a top-up. Tell them the exact code and what the boiler does when it tries — click and nothing, or lights then dies — because that halves the diagnosis. If you don't have an engineer, tell us the code and your postcode and we will match you with a registered local one.
Step by step
- Read the display and note any fault code
Write down exactly what is shown, including any second number or sub-code. If there is no code and the boiler is simply quiet, go to the controls (thermostat, programmer, smart stat) before the boiler.
- Confirm the gas supply
Light the hob. Check a prepayment meter's credit and that the emergency control valve by the meter is fully open. No gas anywhere means the supply, not the boiler.
- Check the pressure gauge
Below about 0.8–1 bar, top up to 1–1.5 bar via the filling loop with the system cold, then reset.
- Check the condensate pipe in freezing weather
Thaw the exposed outdoor section with warm water or a hot-water bottle until you hear a trickle, then reset.
- Reset once and watch
Hold the reset button a few seconds. Fan, clicks, burner. If it locks out again immediately, stop resetting.
- Call a Gas Safe registered engineer
Give them the code and what the boiler does on an attempt. Internal ignition faults — electrode, fan, gas valve, PCB — are engineer-only by law.
Typical costs
| Restoring gas supply, pressure top-up, thawed condensate pipe (DIY) | Free |
| Call-out and diagnosis (typical UK range) | £60–£120 |
| Ignition electrode and lead replacement | £90–£180 |
| Condensate pipe lagging or trace-heating kit fitted | £60–£200 |
| Fan replacement | £200–£350 |
| Gas valve replacement | £250–£400 |
| Control board (PCB) replacement | £250–£450 |
Typical UK ranges as a guide only — prices vary by region (expect the top end, or 20–30% more, in London and the South East) and by how accessible your system is. Always get a written quote.
Frequently asked questions
Why is my boiler not firing up?
Most often because something it needs is missing rather than because it has broken: no gas (empty prepayment meter, closed valve), low water pressure, a frozen condensate pipe in cold weather, or the controls not calling for heat. Check those four, reset once, and if it still tries and fails to light the fault is internal — electrode, fan, gas valve or PCB — and needs a Gas Safe engineer.
Why won't my heating come on but the hot water works?
On a combi that pattern usually points at the controls (thermostat, programmer, smart stat not calling for heat) or the diverter valve stuck in hot-water mode. On a system boiler it can be the motorised valve or pump. See our no-hot-water guide, which covers both directions of this fault.
My boiler clicks but won't ignite — what does that mean?
The clicking is the ignition electrode sparking. If it sparks but never lights, either there is no gas reaching the burner (supply, pressure, gas valve) or the spark is too weak (worn electrode). After checking the gas supply and resetting once, that is an engineer visit — usually a cheap electrode swap.
Why does my boiler only fail to fire on cold mornings?
That is the frozen condensate pipe signature. Thaw the outdoor section with warm water, reset, and then have the pipe lagged, shortened or fitted with a trace heater so it stops recurring.
How many times can I reset my boiler?
Once, after checking gas, pressure and the condensate pipe. If it locks out again straight away, stop — each reset is another failed gas admission. Vaillant and some other brands limit consecutive resets for exactly this reason.
Should I turn my boiler off at the wall if it won't fire?
There is no need unless you smell gas or see a leak — the boiler has already made itself safe by locking out. Leaving it powered also keeps frost protection active on most models. If you smell gas, do not touch electrical switches; leave the property and call 0800 111 999.
How much does it cost to fix a boiler that won't fire up?
Nothing if it is gas, pressure or a frozen pipe. A call-out plus new ignition electrode is typically £90–£180; a fan £200–£350; a gas valve or PCB £250–£450. Regional rates and emergency call-outs vary — get a written quote and check any remaining warranty first.
Is a boiler that won't fire up dangerous?
The lockout is the safety system working — the boiler has stopped because it could not prove a safe flame. The only situation to treat as an emergency is a smell of gas: leave the property and call the National Gas Emergency line on 0800 111 999.