Boiler Problems
Boiler Problems: Straight Answers From The Engineers Who Fix Them
Written & reviewed by our Gas Safe registered engineers · Last updated 22 July 2026
The six guides below cover the boiler faults we’re called out for most often across North London — boilers that switch off, strange noises, pilot lights that won’t stay lit, boilers that won’t start, ignition lockouts and warning lights. Each tells you what we’d actually check first on a job, not a generic checklist.
Quick answer: the six most common boiler faults we’re called out for are a boiler switching itself off, unusual noises, a pilot light that won’t stay lit, a boiler that won’t turn on at all, ignition lockouts, and flashing warning lights. Most trace back to low pressure, a scaled heat exchanger, or a failing sensor — find the guide that matches your symptom below.
Engineer Insight
Why boilers fail — and where homeowners go wrong
Why boilers actually fail
Most faults trace back to one of three things: hard-water scale building up inside the heat exchanger, an electrical or sensor component reaching the end of its life after 8–10 years, or a system that’s never been powerflushed carrying sludge that clogs valves and pumps. London’s hard water makes the first worse than in much of the country — which is why we see kettling and scale-related shutdowns so often on jobs here.
Mistakes we see homeowners make
- Resetting a boiler repeatedly instead of calling after the second lockout
- Ignoring a fault that ‘only happens sometimes’
- Topping up pressure weekly without investigating the leak
- Assuming a working pilot light means the appliance is safe
Guides In This Category
Six common boiler faults, explained
Boiler Keeps Switching Off
Pressure, thermostat or condensate — how to tell which.
Boiler Making Noise
Kettling, gurgling and whistling explained.
Pilot Light Keeps Going Out
Thermocouples, draughts and gas pressure.
Boiler Not Turning On
Power, pressure and PCB faults ruled out in order.
Boiler Not Igniting / Lockout
What lockout actually means and when to reset.
Boiler Flashing Warning Light
How to read the signal before you call.
What Repairs Typically Cost
Typical boiler problem repair costs
If a boiler is over 10 years old and facing a repair above roughly £400, it’s usually worth comparing that cost against a new installation first — see our Buying Guides. You’ll always get an upfront quote before any work starts.
FAQs
Boiler problems — general questions
How can I tell if a boiler fault is urgent or not?
As a rule of thumb: anything involving a gas smell, repeated lockouts, or total loss of heating and hot water in cold weather is urgent. A single warning light with heating and hot water still working is usually safe to book as a standard appointment.
Why does my boiler fault seem to come and go?
Intermittent faults are often the trickiest to diagnose because the problem isn’t present when the engineer arrives. Keep a note of exactly when it happens — time of day, weather, whether the heating or hot water was in use — as this pattern often points straight to the cause.
Does the age of my boiler affect which faults are likely?
Yes. Boilers under 5 years old more commonly have PCB or sensor faults under warranty; boilers over 10 years old are far more likely to be suffering from scale, worn pumps or general component wear.
Should I try to fix a boiler fault myself?
Basic checks like pressure, thermostat settings and fuses are safe. Anything requiring you to open the boiler casing is not — that’s Gas Safe registered work by law, and doing it yourself can also invalidate your warranty and insurance.
Will a boiler fault get worse if I leave it?
Often, yes. A minor pressure or sensor issue left unaddressed can develop into a full lockout or a more expensive repair, particularly if the underlying cause is scale or sludge that keeps building up.
How quickly can Koncore attend a boiler fault?
We offer same-day callouts across Barnet, Camden, Finchley, Hackney, Haringey, Hornsey and Islington — call us and we’ll give you an honest arrival window.
Do all boiler brands fail in similar ways?
The broad categories — ignition, pressure, sensor and pump faults — are common across brands, but the exact fault codes and components differ. See our fault code library for brand-specific guidance.
Is it worth getting a second opinion before agreeing to a repair?
If a repair quote feels high or a replacement is being recommended for a boiler under 8 years old, it’s reasonable to ask for the diagnosis in writing and get a second opinion — we’re always happy to explain our reasoning in plain terms.
Does Koncore charge extra for an out-of-hours or weekend callout?
We’re upfront about any out-of-hours difference before you book, rather than surprising you with it on the invoice — call and ask and we’ll confirm the exact cost for your time slot. Genuine emergencies, like a total loss of heating in freezing weather or a suspected gas leak, are always prioritised regardless of the day or time.
If the engineer diagnoses a different fault than I expected, do I pay for both?
No — you only pay for the diagnostic callout and whatever repair you actually agree to. If the real fault turns out to be different from what you suspected, the engineer will explain what they’ve found and quote for that specific repair before doing any further work, so there are no surprise charges.
Related
More help and our boiler repair service
Look up your code by manufacturer.
Browse libraryHeating ProblemsHeating ProblemsHeating that won't come on or cuts out.
Read guidesPressurePressure ProblemsWhy pressure drops or climbs too high.
Read guidesMaintenanceMaintenanceServicing and warning signs to watch for.
Read guidesBook a boiler repair if you’ve identified the fault, or book a service if it’s just been a while. We serve Barnet, Finchley and Hornsey directly, alongside the rest of North London — see areas we cover.
Still not sure what's wrong?
Describe the fault over the phone and we’ll tell you honestly whether it needs a visit. Gas Safe registered, North London, same-day callouts subject to availability.
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