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Most cold-tap mornings come down to pressure, power or controls — and every one of those is checkable from outside the boiler casing. Work the list in order, then make the call.
The short version: check the boiler's pressure gauge (roughly 1 to 1.5 bar cold), the thermostat and timer, and the fused spur and consumer unit for a tripped switch — and in winter, a frozen condensate pipe. Never open the boiler casing itself. Still cold? Ring 020 4577 2888 at any hour to be connected with a local plumber covering Banbridge.
Five minutes of method rules out the causes that would be embarrassing to pay for. Do them in this order and stop the moment the hot water returns.
That split is one of the most useful clues in boiler diagnosis. On a combi, hot radiators with cold taps often point at the diverter valve — the small internal part that switches the boiler between heating and hot water. It is not something you can reach or fix yourself, but naming the symptom on the phone tells the plumber a great deal before the van moves.
Plenty of the older houses near the town centre still run cylinder systems extended over the decades, while the newer estates are mostly combi territory — knowing which you have is the first question you will be asked.
In a cold snap, a boiler that was fine yesterday and silent today has a prime suspect: the condensate pipe, the plastic run that carries condensation to a drain — often down an outside wall, where a freezing night can block it solid and shut the boiler down in protest.
Two hard lines, and they are not negotiable. First: the boiler casing stays shut. Anything behind it is legally work for an engineer on the Gas Safe Register — checking pressure, controls and the condensate pipe never requires opening the box. Second: if you smell gas at any point, stop troubleshooting entirely. Leave the property, touch no switches on the way out, and call the National Gas Emergency Service on 0800 111 999 from outside. Everything else on this page can wait behind those two rules.
No — that box stays shut. In the UK, work behind the casing of a gas boiler is legally reserved for an engineer on the Gas Safe Register, and there is nothing in there a homeowner can safely adjust. Everything on this page — pressure, controls, switches, the condensate pipe — sits outside the casing, and that is where your checks end.
Roughly 1 to 1.5 bar with the system cold, for most sealed-system boilers — your manual gives the exact band for your model. Below about 1 bar, a top-up through the filling loop is usually a homeowner job. If the pressure keeps sliding back down over days or weeks, stop topping up and have the leak traced instead.
Two extra checks. First, the cylinder thermostat — if it has been knocked low, the water will be tepid rather than hot. Second, the immersion heater: most cylinders have one as a backup, switched at the wall, so flicking it on can restore hot water while the main fault is being fixed. If the immersion works but the boiler route does not, tell the plumber — that narrows the fault nicely.
Quite possibly, especially if the system was recently drained or worked on. An airlock is a pocket of trapped air stopping the water flowing properly, and it tends to affect one tap or one run rather than the whole house. Some clear themselves; stubborn ones are a quick job for a plumber rather than something to improvise at with hosepipes.
Stop checking. A gas smell outranks everything on this page: leave the property, touch no switches or flames on the way out, and call the National Gas Emergency Service on 0800 111 999 from a safe distance outside. The hot water can wait; ring the plumbing line afterwards for the repair.
The main page — how the line works and the 60-second checklist.
Go to home →Pressure, lockouts, error codes — and the gas checklist first.
Open the checklist →Water off, taps open, electrics safe — the first five minutes.
Open the checklist →Prevention, gentle thawing from the tap end back — never a flame.
Open the checklist →Damp patches, dropping pressure, and the stopcock test.
Open the checklist →What to try, what never to pour away, when it is the main drain.
Open the checklist →National ballparks with caveats, and the questions to ask first.
Open the checklist →Ring at any hour with your notes ready — combi or cylinder, what failed, the pressure reading, any error code — and be connected with a local plumber covering Banbridge and the surrounding area.
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