Boiler not working? Here’s what it usually means
Guidance last checked on against UK safety regulation and the sources behind our service pages.
A boiler that won't run almost always comes down to one of five things. Check the pressure gauge and the display code first: low pressure, a frozen condensate pipe in cold snaps, an error code, a failed pump or valve, or no gas supply — between them, they cover most faults.
Boiler not working: the questions people ask
Why does my boiler show a pressure fault?
The pressure gauge on the front of the boiler reads below 1 bar, and the boiler locks out once pressure falls far enough. Repressurise it through the filling loop (the flexible braided hose under the boiler, shown in the manual) until the needle sits around 1.5 bar. If it keeps dropping again over following days rather than holding, there is a leak somewhere in the system or a failing expansion vessel, and that is a repair, not a top-up.
Why has my boiler locked out with a gurgling noise?
In a hard frost, the white plastic condensate pipe that carries the boiler's waste water outside can freeze solid and lock the boiler out, often with a gurgling or bubbling noise just before it stops. Find the pipe where it leaves the wall and thaw it gently by pouring warm — never boiling — water along its length, or wrapping it in a hot water bottle, then reset the boiler once it drains freely again.
What does my boiler's error code mean?
The digital display names the component that has failed — a sensor, the fan, the ignition system, or the circuit board — and that code is the fastest route to a diagnosis, so read it before calling anyone. One reset is worth trying once the cause looks minor, but a boiler that locks out again straight after a reset has a real fault developing, and repeated resets can turn a cheap part into an expensive one.
Why is the boiler running but nothing gets warm?
The circulating pump or a motorised valve can fail while the boiler itself is perfectly healthy: the burner fires and the display looks normal, but nothing in the house gets warm, and on some models the boiler locks out rather than run with no water moving. It sounds dramatic but is usually a contained, repairable part swap, not the start of a boiler replacement.
Why has my boiler lost gas supply?
If the hob or any other gas appliance in the house is also dead, the boiler is very likely starved of gas rather than faulty itself. Check the gas meter for a tripped emergency control valve, and check any prepay credit has not run out. A smart meter stuck in 'off' mode after a power cut is a surprisingly common, easily missed culprit worth ruling out before booking a Gas Safe engineer.
Related symptoms
What to check, in order
1. Note the error code and the pressure reading first
Before resetting anything, write down what the display shows and where the pressure needle sits. The code names the component that has failed, and a reading below 1 bar is low; the boiler locks out once pressure falls far enough.
2. Check whether your other gas appliances work
If the gas hob or any other gas appliance in the house is dead too, the boiler is very likely starved of gas rather than faulty. Check any prepay credit, and whether a smart meter is stuck in off mode after a power cut.
3. Check the condensate pipe outside in a frost
In freezing weather, find the white plastic pipe where it leaves the wall. A gurgling noise before the lockout points to ice inside it. Thaw it with warm, never boiling, water, then reset the boiler once it drains freely.
4. Top up the pressure only if the gauge reads low
If the needle is below 1 bar, repressurise through the filling loop exactly as your boiler manual shows, to around 1.5 bar. If it drops again rather than holding, stop topping up: that is a leak or a failing expansion vessel.
5. Reset the boiler once, and only once
With the pressure and the condensate pipe ruled out, try one reset, unless you already reset it after thawing the pipe. If it locks out again straight afterwards, stop there: repeated resets can turn a cheap part into an expensive one.
6. Book a Gas Safe engineer with what you found
If the burner fires but nothing warms, or the boiler locks out again after one reset, it needs a Gas Safe engineer. Book a visit and pass on the error code, the pressure reading and what you have already ruled out.
What not to do
- Don't remove the boiler casing — what's behind it is gas work, which the law allows only someone competent to do, and any engineer you pay to do it must be Gas Safe registered
- Don't keep force-resetting a boiler that locks out repeatedly
- Don't run the boiler if it's leaking water onto electrics
- If you smell gas, or a carbon monoxide alarm sounds: don't smoke, light a flame or touch light switches, open the doors and windows, turn the gas off at the meter if you can reach it safely and it isn't in a cellar or basement, get everyone out, and call the National Gas Emergency Service free on 0800 111 999 before anything else — before calling us
When to request help
If pressure top-up and one reset don't restore it, it needs a Gas Safe registered engineer. Treat it as a same-day job if you have no heating in cold weather, or vulnerable people at home.
Request a Hero through London Heroes: every Hero must pass identity verification before they can take work, and your payment is held until you confirm the work is complete. How requesting works
Related questions
How much does a boiler repair cost in London?
My boiler works for heating but not hot water — same problem?
General guidance, not a substitute for an on-site professional assessment — and never for the gas emergency line (0800 111 999) if you smell gas.