Simple checks before you call
- Is the gas supply on, and do other gas appliances work?
- Is the boiler showing a fault code? Look it up in the manual.
- Is the pressure gauge in the range the manual gives? Low pressure is a common cause of combi boilers stopping. Many manuals explain how to top it up.
- Are the thermostat, timer and any smart controls set correctly, with working batteries?
- In freezing weather, a frozen condensate pipe can stop condensing boilers. Some manufacturers explain how to thaw it safely with warm (not boiling) water.
Never remove the boiler casing or try to repair gas parts yourself. If you smell gas, call 0800 111 999 (Great Britain) or 0800 002 001 (Northern Ireland).
Why Gas Safe registration matters
By law, anyone working on gas appliances in Great Britain, Northern Ireland, the Isle of Man and Guernsey must be on the Gas Safe Register. Check the business on the register and ask to see the engineer's ID card. The back of the card lists the kinds of gas work they're qualified to do, such as boilers or cookers.
Servicing and landlords
A service checks the boiler is working safely and efficiently, and many manufacturers need one each year to keep the warranty valid. Landlords must have gas appliances they provide checked every 12 months by a Gas Safe registered engineer and give tenants a copy of the gas safety record.
Carbon monoxide
A faulty boiler can produce carbon monoxide (CO), which you can't see or smell. Symptoms include headaches, dizziness, nausea, breathlessness and tiredness. Fit an audible CO alarm, and if you suspect CO, get fresh air, turn off the appliance if you can, call the gas emergency number and seek medical advice.
Repair or replace?
Ask engineers for written quotes for both repair and replacement if your boiler is older or keeps breaking down. Compare the parts warranty, labour guarantee, the boiler's efficiency rating and whether the quote includes system cleaning and controls. Government schemes for heat pumps and efficiency upgrades change over time, so check GOV.UK for what's currently available.
Last updated: 14 October 2026
