Smell gas? Don't touch electrical switches. Open windows, turn the gas off at the meter and call the National Gas Emergency Service on 0800 111 999 before anything else.
First steps when your boiler stops working
- 1If you can smell gas, don't touch switches — open windows, turn the gas off at the meter and call the National Gas Emergency Service on 0800 111 999.
- 2If water is leaking, turn off the internal stopcock and the boiler's isolation valves to stop further damage.
- 3Check the boiler pressure gauge. Below roughly 1 bar usually means it needs re-pressurising.
- 4Check your thermostat, timer and that the gas supply and other appliances are working.
- 5Note the fault code shown on the display — it tells the engineer a lot before they arrive.
Common boiler faults and what they mean
No hot water or heating
Often a failed diverter valve, pump or a stuck thermostat. Worth checking the timer and thermostat batteries first.
Boiler losing pressure
Usually a leak on the system, a failed expansion vessel or a passing pressure relief valve. Re-pressurising repeatedly is a sign of a real fault.
Boiler locking out / repeated resets
Ignition, flame sensing or fan faults. Never reset more than a couple of times — repeated lockouts need a Gas Safe engineer.
Frozen condensate pipe
Common in winter and often shows a gurgling noise. Thawing the external pipe with warm (not boiling) water frequently fixes it.
Radiators cold at the top
Trapped air — bleed the radiators, then top the pressure back up. Cold at the bottom usually means sludge and a flush.
Leaking or dripping boiler
Turn the boiler off and isolate the water. Leaks inside the case are never a DIY fix.
When to call an engineer straight away
- You can smell gas or the carbon monoxide alarm has sounded
- The boiler is leaking water or there are scorch marks around the case
- The boiler locks out again immediately after a reset
- There's no heating or hot water and someone in the home is elderly, unwell or very young
- Pressure keeps dropping within hours of topping it up
Frequently asked questions
Is a broken boiler an emergency?
If there's a gas smell, a water leak or no heating for a vulnerable person, treat it as an emergency and call straight away. Otherwise it can usually be booked as a same-day or next-day repair.
How quickly can you get to me?
We offer 24/7 call outs across Greater Manchester and aim to attend emergencies the same day. Call 03330704021 and we'll give you a realistic arrival time.
Can I repair my own boiler?
No. By law, work on gas appliances must be carried out by a Gas Safe registered engineer. You can safely check pressure, the thermostat and the timer.
Repair or replace?
If the boiler is under about 10 years old and the part is available, a repair is usually the sensible option. Repeated breakdowns or an obsolete part often mean replacement is better value.
Boiler down? We're on the way.
Gas Safe registered engineers covering Greater Manchester — 24/7 call outs, no hidden costs and a 1 year warranty on our work. Rain or shine, Semico is on time.