A boiler that does not fire may leave you without heating, hot water or both. Sometimes the cause is an external control or an interruption to the supply; in other cases, the boiler has detected a fault and stopped to protect the system.
A few checks can be made without opening the appliance. If those checks do not restore normal operation, professional testing is the safest next step.
Check what is—and is not—working
Confirm whether the issue affects heating, hot water or both. A combi boiler that heats radiators but not tap water points to a different area from a boiler with no display or response at all. Check whether other gas appliances are operating normally, but do not attempt to work on the gas supply.
Look at the programmer, room thermostat and boiler display. Make sure the controls are switched on and requesting heat. If a timer lost its settings after a power interruption, restore the programme using its instructions.
Safe checks before calling
Read the pressure gauge and compare it with the range stated in the manufacturer’s manual. Check for an error code and follow only the user actions described in that manual. A single reset may be appropriate for some faults, but repeated resets should be avoided.
- Confirm that the thermostat is set above the current room temperature.
- Check that the boiler and heating controls have electrical power.
- Record any fault code exactly as it appears.
- Look for visible leaking without removing the boiler cover.
Common faults that need professional testing
Ignition components, sensors, pumps, valves, fans and control boards can all prevent a boiler from starting correctly. Low system pressure, restricted circulation or a blocked condensate route may also cause a lockout. Similar symptoms can come from different faults, so replacing parts without testing is unreliable.
Do not remove the boiler casing or try to adjust gas components. Gas work must be handled by a Gas Safe registered engineer with the right equipment for combustion and safety checks.
When the problem is urgent
Seek urgent help if you smell gas, suspect carbon monoxide, see significant water leakage or have vulnerable occupants without heating during cold conditions. If you smell gas, follow the emergency guidance from the National Gas Emergency Service and do not operate electrical switches in the affected area.
For boiler breakdowns across North London, TREPP & CO provides fault-finding, repair and 24/7 emergency call-outs. Share the boiler model, fault code and the checks you have already made when you call.
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