Boiler Problems
Boiler Not Igniting? Lockouts and Ignition Faults Explained
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
When your boiler tries to fire but locks out, it’s usually pressure, gas or the condensate pipe — not always an expensive fault. Here’s how to tell what’s going on, and when to call a Gas Safe engineer.
Quick answer: An ignition lockout means the boiler tried to light but couldn’t, so it shut down for safety. The usual causes are low pressure, a frozen condensate pipe, or a gas supply issue — all worth checking first. One reset is fine; if it locks out again, or you can smell gas, stop and book a Gas Safe engineer.
Common Causes
Why a boiler won’t ignite
These are the causes we see most, roughly in order. The colour on the left of each row shows whether it’s usually a safe homeowner check or a job for an engineer.
| What happens | Likely cause | What to do |
|---|---|---|
| Clicks then locks out | Failed ignition — electrodes or gas | Try one reset; if it recurs, book an engineer |
| Lockout on cold mornings | Frozen condensate pipe | Thaw the external white pipe, then reset |
| Lockout with low pressure | Pressure has dropped below 1 bar | Repressurise to ~1.3 bar, then reset |
| No gas reaching the boiler | Gas supply or meter issue | Check other gas appliances; if none work, call your supplier |
| Locks out again and again | Worn electrodes, PCB or gas valve | Needs a Gas Safe engineer to diagnose |
| Yellow or lazy flame | Combustion problem | Turn the boiler off and call an engineer |
Safe Checks
What you can check before calling
Safe to check
- The pressure gauge reads around 1.3 bar (top up if low)
- The external condensate pipe hasn’t frozen
- Other gas appliances in the home are working
- Try one reset only — never repeatedly
Stop and call us if…
- You can smell gas — leave the property and call 0800 111 999
- The boiler locks out again after one reset
- The flame looks yellow, or you see soot around the boiler
Engineer Insight
What we usually find
Most ‘won’t ignite’ call-outs in North London come down to pressure, or a frozen condensate pipe in winter — both quick, inexpensive fixes. Repeated lockouts point to worn ignition electrodes, the gas valve or the PCB. We confirm the cause before quoting, so you’re never paying for guesswork.
Costs
Typical ignition repair costs
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Boiler not igniting — your questions answered
What does an ignition lockout mean?
It means the boiler tried to light but the flame didn’t establish, so it shut down for safety. It’s a protective feature, not necessarily a serious fault.
How many times can I reset the boiler?
Once. If it locks out again after a single reset, stop — repeated resetting can be unsafe and won’t fix the underlying cause. Book a Gas Safe engineer.
Can a frozen condensate pipe stop ignition?
Yes, very commonly in winter. The external white pipe freezes and blocks. Thawing it gently with warm (not boiling) water and resetting the boiler often solves it.
Is a boiler that won’t ignite dangerous?
The lockout itself is a safety response. But if you can smell gas, or see a yellow flame or soot, treat it as urgent — turn the boiler off and call the Gas Emergency Service on 0800 111 999.
How much does an ignition repair cost?
A diagnostic visit is typically £80–£120 in North London. Replacing ignition electrodes runs around £120–£260; a gas valve more. You’ll get an upfront quote first.
Related
Keep troubleshooting
No display, no response — power, pressure and thermostat checks.
Read guideBoiler ProblemsPilot Light Keeps Going OutOn older boilers — thermocouple, draughts and gas supply.
Read guidePressureLow Boiler PressureA common cause of lockouts — why it drops and how to fix it.
Read guidePressureHow to Repressurise a BoilerStep-by-step: top your boiler back up to 1.3 bar with the filling loop.
Read guidePressureBoiler Losing PressureIf pressure keeps dropping and triggering lockouts.
Read guideFault CodesBoiler Fault Code LibraryLook up the exact code by brand — Worcester, Vaillant, Ideal and more.
Browse codesBrowse all Boiler Problems guides, or head back to the Help & Advice Centre.
Locked out and won’t reset? We’re Gas Safe.
Book a Gas Safe engineer to find out why it’s locking out, or call and tell us what the boiler’s doing — we’ll give you an honest steer first.
Gas Safe Registered 918817 | North London specialists | Upfront pricing