Cold taps don't always mean a broken boiler. Work through these checks in order — a good share of "no hot water" mornings end without a call-out at all.
No hot water in Larne — what should I try first? Check the boiler's pressure gauge — most combis want roughly 1 to 1.5 bar cold, topped up via the filling loop — then the thermostat, the timer and any tripped switch or fuse. Heating fine but taps cold? That points at the diverter valve, an engineer's job. Never open the boiler casing yourself, and if you smell gas, leave the property and call 0800 111 999 from outside.
Start with the unglamorous checks, because they solve more of these than anyone likes to admit. Is the boiler actually on — has the fused spur or a trip switch on the consumer unit gone without you noticing? Is the room thermostat turned up, with live batteries? Has the timer or clock drifted — a power cut can leave a boiler quietly convinced it's 3am — and is it actually calling for hot water at the time you want it? Then look at the pressure gauge: below about 1 bar cold, many boilers simply refuse to fire, and on most combis you can top up through the filling loop yourself, following your manual, until the needle sits around 1 to 1.5 bar. Five minutes on these before you ring anyone.
On a combi boiler, that split personality is the classic sign of a sticking diverter valve — the internal part that swaps the boiler's output between radiators and taps. When it sticks, you get one or the other, not both. There's no dial to fiddle with for this one: the valve lives behind the casing, and anything behind the casing is legally a job for a Gas Safe registered engineer. Mention the symptom when you call — "heating works, hot taps don't" — because it narrows the diagnosis before anyone arrives.
Plenty of homes around Larne — particularly older houses and bungalows out towards Kilwaughter, Gleno and Islandmagee that have been updated piecemeal over the decades — still heat water in a cylinder rather than on demand. If that's you, check whether the immersion heater has its own switch that's been knocked off or tripped, whether the cylinder thermostat is set sensibly (around 60°C is the usual guidance), and whether the programmer is actually scheduling hot water and not just heating. An immersion heater can also serve as a stopgap: if the boiler side has failed, switching the immersion on may buy you hot water while you wait.
In a cold snap, a frozen condensate pipe is the classic reason a healthy boiler goes on strike — the plastic pipe running outside freezes, the boiler locks out, and everything stops. Thaw the outdoor section gently with warm (not boiling) water, then reset once, per your manual. Airlocks are winter's other trick: if a tap splutters and spits after pipework has been drained or a freeze has passed, trapped air may be blocking the flow, and a plumber can bleed it through properly.
If you smell gas, this page — and this phone line — is the wrong place. Leave the property straight away. Don't touch light switches or electrical appliances, don't use naked flames, and don't try to find the leak yourself.
Once you're outside and at a safe distance, call the National Gas Emergency Number on 0800 111 999. A plumbing line is not the right contact for a suspected gas leak. And any work on a gas boiler must legally be done by a Gas Safe registered engineer.
On a combi boiler, radiators that heat up while the taps run cold is the classic sign of a sticking diverter valve — the part that switches the boiler between heating and hot water. It's an internal component, so diagnosing and replacing it is a job for a Gas Safe registered engineer, not a screwdriver moment.
No. Never open the boiler casing yourself — anything behind it is legally a job for a Gas Safe registered engineer. The checks that are safe for you are all on the outside: the pressure gauge, the thermostat and timer, the power switch, and the condensate pipe outdoors.
Most combi boilers want roughly 1 to 1.5 bar when cold, though your own manual is the final word. Below about 1 bar, many boilers refuse to heat water; you can usually top up through the filling loop yourself. If the pressure keeps falling after you top it up, stop refilling and get the system checked — repeated loss points to a leak.
Quite possibly. In freezing weather the boiler's condensate pipe — the plastic pipe that usually runs outside — can freeze and lock the boiler out entirely. Thawing the outdoor section gently with warm, not boiling, water and then resetting the boiler often brings everything back without a call-out.
Leave the property straight away, don't touch light switches or electrical appliances, and don't use naked flames or try to find the leak yourself. Once you're outside and at a safe distance, call the National Gas Emergency Number on 0800 111 999. A plumbing line is not the right contact for a suspected gas leak.
The main page — what this line is and how it works.
Go to home →The first five minutes: stopcock, taps, electrics.
Read the guide →Pressure basics, no heat, error codes — and gas safety.
Read the guide →What to try first and when it's a main-drain problem.
Read the guide →Prevention, gentle thawing — and what never to use.
Read the guide →Damp patches, dropping pressure and the stopcock test.
Read the guide →Honest ballparks and the questions to ask before work starts.
Read the guide →Call any time, day or night, to be connected with a local plumber covering Larne and the surrounding villages.
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