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Pressure drops, cold radiators, cryptic codes on the display — most boiler trouble speaks a language you can learn in five minutes.
My boiler's stopped working — what do I actually do? Check the gauge first: if pressure sits below about 1 bar, top up once through the filling loop using your boiler's manual. Note any error code on the display, try one reset, and if it won't come back — or the same fault returns — ring 020 4577 2888 to be put through to a local plumber. If you smell gas, skip all of this: leave the house and call 0800 111 999.
Because the water in your sealed heating system is escaping somewhere. Once is life; repeatedly is a leak that wants finding.
The gauge on the front of most sealed-system boilers should sit around 1 to 1.5 bar when the heating is cold — your manual gives the exact happy zone for your model. Dip below roughly 1 bar and the boiler sulks: lukewarm radiators, lockouts, sometimes a low-pressure code on the display. Repressurising through the filling loop is a legitimate DIY job, and doing it once or twice a year after bleeding radiators is nothing to worry about.
What deserves your suspicion is the pattern. If you topped up last week and the needle is already sagging again, the system is losing water somewhere — a weeping radiator valve, a joint under the floor, a pinhole you'll never spot from outside. Every top-up adds fresh water and fresh oxygen to the system, quietly feeding corrosion while the leak feeds itself. That's the point to stop treating the symptom and get the cause traced. And if the gauge sits high instead — up past 2.5 or 3 bar — suspect a filling loop that wasn't closed fully or an expansion vessel fault, and mention the reading when you ring.
Five checks, two minutes, no tools: power, controls, pressure, condensate pipe, one reset. A surprising share of "dead" boilers come back after this list.
If the list doesn't fix it, you've lost two minutes and gained a much better phone conversation, because you can tell the plumber exactly what you checked and what the display says.
It's the boiler's own shorthand for what hurt — and it means different things on different makes. Write it down exactly; don't clear it and don't guess.
Every manufacturer runs its own code system, so the same jumble of letters and numbers can mean low pressure on one boiler and an ignition fault on another. The only reliable translator is your own boiler's manual — most are findable online with the model number if the paper copy vanished years ago. Codes broadly sort into themes: pressure and circulation, ignition and flame detection, fans and sensors, and condensate drainage.
Two habits serve you well here. First, record the code before touching anything — photograph the display, since a reset can wipe the very clue an engineer needs. Second, resist the urge to reset over and over; one attempt is diagnosis, five attempts is punishment, and a boiler that repeatedly locks out on an ignition or flame fault is asking for a professional, not persistence. Codes suggesting anything about flame, combustion or gas supply are strictly look-don't-touch territory.
Leave the house now and call the National Gas Emergency Service on 0800 111 999 from outside. Not a plumber, not this line — that number, first.
A gas smell is the one situation on this page where you should stop reading and act. Get everyone out of the property. On the way, touch nothing electrical — no light switches on or off — and no flames, no cigarettes, no ringing your phone until you're outside at a safe distance. Don't open up walls or go hunting for the source; that's the emergency service's job, and they run 24 hours a day.
Once the property has been made safe, then and only then does a plumber or heating engineer come into the picture for any repair work. Remember that anyone working on gas appliances in the UK must be Gas Safe registered by law — asking to see the card is normal, not rude. This plumbing line is the right call for boilers, leaks and pipework; for suspected gas escapes it is emphatically the wrong first call, and we'd rather tell you that plainly than ever be dialled first in that situation.
Topping up once in a while is normal life with a sealed system. Topping up every week is a leak wearing a disguise — the water is going somewhere, often into a wall or under a floor where it does quiet damage. If the gauge keeps falling, stop feeding it and have the system traced properly.
Once is a fair try — a single reset after a fault clears plenty of one-off lockouts. If the boiler locks straight back out again, stop. Repeated resets just hammer a boiler that's telling you something is wrong, and the fault code it's showing helps a professional far more than a wiped history does.
In the UK, anyone working on gas appliances must be Gas Safe registered — it's the law, not a nice-to-have. When any engineer arrives for gas work, it's completely reasonable to ask whether they're Gas Safe registered and to see the ID card. Oil-fired boilers, common in rural homes around here, have their own separate technician registrations — ask about those too.
A frozen condensate pipe is the classic culprit — the little plastic pipe that drains acidic water from a condensing boiler, often out through an external wall. When it freezes, the boiler shuts itself down. Thawing that pipe gently with warm (never boiling) water poured along it, then resetting the boiler, fixes many a cold-snap breakdown without a call-out.
The main page — how the line works and the areas it covers.
Go to home →The first five minutes, in the right order.
Read the guide →What to try yourself and when it's the sewer, not your drain.
Read the guide →Honest ballparks and the questions to ask before work starts.
Read the guide →Pressure, controls, the immersion — the checks before you call.
Read the guide →Thawing safely with gentle heat — and the lagging that prevents it.
Read the guide →Damp patches, dropping pressure and the stopcock test.
Read the guide →Ring any hour to be put through to a local plumber covering Newry and the surrounding towns and townlands — code, gauge reading and all.
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