Maintenance
Signs Your Boiler Needs Servicing
Reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
A boiler rarely fails without warning. These are the signs it’s due a service — some routine, a couple that mean ‘book it now’ — plus why an annual check pays for itself in avoided breakdowns and lower bills.
Quick answer: Book a service if you notice any of these — a yellow or orange flame instead of crisp blue, a faint smell around the boiler, banging or gurgling noises, creeping gas bills, pressure that keeps dropping, or simply that it’s been over a year. A yellow flame, a smell, or any sooting means stop using it and book straight away, as those can point to incomplete combustion.
The Signs
Seven signs your boiler is overdue
Some of these just mean it’s time to book a service; a few mean stop using the boiler now. The colour on the left tells you which.
| The sign | What it usually means | What to do |
|---|---|---|
| It’s been more than 12 months | Service overdue | Book a routine annual service |
| Gas bills creeping up | Boiler losing efficiency | Book a service to clean and re-tune it |
| Banging, gurgling or whistling | Sludge or limescale in the heat exchanger | Book a service; a powerflush may be advised |
| Yellow or orange flame | Incomplete combustion | Stop using it and call us now — this can mean carbon monoxide |
| A smell around the boiler | Possible fuel or flue issue | Turn it off and call us; if you smell gas, call 0800 111 999 |
| Pressure keeps dropping | A small leak or failing part | Top up once, then book a service to find the cause |
| Black marks or soot on the case | Sooting from poor combustion | Stop using it and call us now — sooting means unsafe combustion |
First Steps
What to check yourself
Worth doing
- Book an annual service if it’s been more than 12 months
- Glance at the flame through the viewing window — it should be crisp blue, not yellow
- Note any new banging, gurgling or whistling when the heating runs
- Keep an eye on the pressure gauge and your gas bills for creeping changes
Stop and call us if…
- The flame is yellow or orange, or there’s sooting around the case
- You can smell gas — call 0800 111 999 — or notice any burning smell
- Your carbon monoxide alarm sounds, or anyone feels unwell or drowsy
- The boiler keeps losing pressure or locking out
Engineer Insight
What a service actually does
A service isn’t just a tick-box. We check the flue and combustion (the safety-critical part), clean the condensate trap and burner, test the pressures, and catch worn seals and a tired expansion vessel before they leave you cold in January. Most winter breakdowns we attend would have been spotted at a service — and a boiler running clean uses noticeably less gas. If yours is still under manufacturer warranty, an annual service is usually a condition of keeping it valid.
Costs
What servicing typically costs
Typical North London guide prices — you’ll always get an upfront quote before any work starts.
FAQs
Boiler servicing — your questions answered
How often should a boiler be serviced?
Once a year. It keeps the boiler running safely and efficiently, is usually required to keep the manufacturer’s warranty valid, and catches small faults before they become winter breakdowns.
What are the warning signs a boiler needs servicing?
A yellow rather than blue flame, a faint smell around the boiler, banging or gurgling noises, rising gas bills, pressure that keeps dropping, and simply being over a year since the last service. A yellow flame or any smell means book straight away.
Is it safe to use a boiler that’s overdue a service?
If it’s running normally, a slightly overdue service isn’t an emergency — just book it soon. But a yellow flame, a smell, sooting, or a sounding CO alarm means stop using it and call us now, as those can point to unsafe combustion.
Does servicing my boiler actually save money?
Usually yes. A clean, correctly tuned boiler burns less gas, and a service catches cheap fixes (seals, a failing vessel) before they turn into expensive breakdowns. It also protects your warranty.
What happens during a boiler service?
We check the flue and combustion, inspect and clean the burner and condensate trap, test the gas pressure and safety devices, check the seals and expansion vessel, and give you a written summary of the boiler’s condition.
Related
Related guides
Servicing prevents most winter breakdowns.
Read guidePressureBoiler Losing PressureRepeated pressure loss is a service red flag.
Read guideBoiler ProblemsBoiler Making NoiseBanging and kettling, explained.
Read guideLeaksBoiler Leaking WaterWorn seals often start to leak first.
Read guideCentral HeatingPowerflush GuideFor kettling caused by sludge in the system.
Read guideBoiler ProblemsBoiler Not Turning OnWhen a warning sign becomes a no-start.
Read guideBrowse all Maintenance guides, or head back to the Help & Advice Centre.
Due a service? Let’s keep it running.
Book an annual service with a Gas Safe engineer, or call — we’ll keep your boiler safe, efficient, and warranty-valid across North London.
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