Before assuming the worst, check the simple things: boiler pressure around 1 to 1.5 bar when cold, the thermostat and timer actually asking for hot water, and the boiler's fused switch not tripped. If the heating works but the taps run cold on a combi, suspect the diverter valve. Never open the boiler casing yourself — and if you smell gas at any point, leave the house and call 0800 111 999 from outside.
If you smell gas, stop reading and leave
Leave the property now. Do not touch light switches, doorbells or anything electrical, and do not use a naked flame. From outside, call the National Gas Emergency Number on 0800 111 999 — free and staffed 24/7. A plumbing line is not the right contact for gas.
Is it the boiler, or just the settings?
A surprising share of "no hot water" calls end at the controls. Start at the pressure gauge: most sealed-system boilers sit happily between 1 and 1.5 bar when cold, and below 1 bar many simply refuse to fire. Topping up with the filling loop, following the boiler's manual, is a normal homeowner job. Then look at the thermostat and timer — after a power cut, a timer's clock can drift hours out, so the boiler is heating water faithfully at 3am and doing nothing at teatime. Check the boiler's fused switch on the wall hasn't been knocked off, and that a trip in the consumer unit hasn't quietly cut it. None of this costs anything, and any one of them can be the whole story.
Why does the heating work but the taps run cold?
On a combi boiler, that split personality usually points to the diverter valve — the component that swaps the boiler's effort between radiators and taps. When it sticks or wears, one side wins and the other goes cold. It's one of the most common combi faults, and it's an engineer's repair, not a homeowner one. What you can usefully do is note the pattern precisely — heating fine, hot tap cold, or the reverse — and say so when you call; it genuinely shortens the visit.
What if my home has a hot water cylinder?
Plenty of houses around Ballymena — older properties in the terraced streets near the town centre, and many rural homes out toward Broughshane or Kells — heat water in a cylinder rather than on demand. Two extra checks apply. First, the immersion heater: if the cylinder has one, it has its own switch and often its own fuse, and either can trip. A working immersion can also keep hot water flowing as a stopgap while a boiler fault waits for repair. Second, airlocks: if a hot tap splutters, hisses and then gives nothing after work on the system or a drained tank, trapped air rather than a failed boiler may be the culprit — mention it when you phone rather than dismantling anything.
Could winter be the culprit?
In the hard frosts that reach in from Glenwherry and Cargan, the boiler's condensate pipe — the narrow plastic pipe that often runs down an outside wall — can freeze solid and shut the boiler down with a fault code. Thawing it gently with warm (not boiling) water or a hot water bottle, then resetting the boiler once, often brings everything back. If frozen pipework elsewhere in the house is starving a tap, our frozen pipes guide covers thawing it safely.
When should I stop and call someone?
Draw the line at the casing. Everything behind it, gas side included, must legally be handled by a Gas Safe registered engineer — no exceptions, however handy you are. Stop too if the same fault code returns after one reset, if the pressure keeps sagging after every top-up, or if there's any noise, smell or scorch mark around the boiler. At that point the honest advice is to switch the system off and pick up the phone.
Common questions about lost hot water
Why is there no hot water when the heating still works?
On a combi boiler, radiators that heat while the taps run cold usually point to the diverter valve — the component that switches the boiler between heating and hot water. It's a known wear item, and it's a repair for an engineer rather than something to attempt yourself. Describe the pattern when you call; it narrows the diagnosis before anyone arrives.
Can I top up my boiler pressure myself?
Usually, yes. Most sealed-system boilers can be safely repressurised by the homeowner using the filling loop, following the instructions in the boiler's manual — aim for the range the manufacturer recommends, typically around 1 to 1.5 bar when cold. If the pressure keeps dropping again within days, the system is losing water somewhere and needs looking at rather than topping up forever.
Is it safe to open the boiler casing to have a look?
No. Never open the boiler casing yourself — everything behind it, including the gas side, must legally be worked on by a Gas Safe registered engineer. The checks that are safe for a homeowner all sit outside the casing: the pressure gauge, the filling loop, the thermostat, the timer and the fused switch.
What is an immersion heater and do I have one?
If your home has a hot water cylinder — common in older properties and many rural houses — it may have an electric immersion heater fitted, usually with its own switch nearby. It heats the cylinder independently of the boiler, so it can serve as a backup for hot water while a boiler fault is being fixed. Check whether its switch or fuse has tripped before assuming the element has failed.
Could the cold weather have stopped my hot water?
Quite possibly. In a hard frost the boiler's condensate pipe — the small plastic pipe that often runs outside — can freeze and shut the boiler down with a fault code. Thawing it gently with warm (not boiling) water or a hot water bottle, then resetting the boiler, often restores everything. Never use a naked flame.
More help
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