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Safety first: if you smell gas, evacuate the property immediately and call the gas emergency number. Do not attempt repairs if you are unsure; qualified engineers must work on gas components. Isolate mains power before removing covers. Only carry out visual checks and control changes that do not require opening the boiler casing.

Initial quick checks homeowners can do:

1. Check mains electricity to the boiler is ON and any external fused spur or switch is turned on. The boiler needs mains power to operate.

2. Check the boiler mode knob (B) is set to BOILER ON or the required position for heating/hot water. If set to BOILER OFF the display will show 00 (standby).

3. Check your programmer/timer is set to call for heating or hot water at the current time. Ensure the programmer is set to ON and the schedule/time settings are correct.

4. Check the room thermostat is set higher than the room temperature and the hot water cylinder thermostat (if fitted) is calling for heat. Turn them up briefly to test.

5. Check the boiler’s central heating temperature knob is not set very low; set to a mid/high setting for test (manual suggests MAX when starting).

6. If the boiler has a pressure gauge (sealed system), confirm system pressure is roughly 1.0–1.5 bar. Very low pressure can prevent normal operation.

If the boiler is still in standby when you expect heat or hot water:

1. Try a simple restart: press the boiler RESTART/RESET button per the manual. Wait for the ignition sequence; if it fails repeatedly an error/lockout code will appear and you should follow fault guidance or call an engineer.

2. Power-cycle the boiler: switch off at the mains for 30 seconds and switch back on, then set mode to BOILER ON and observe the display.

3. If pressure is low (below ~1.0 bar) and you are familiar with your filling loop, top the system up to around 1–1.5 bar following the boiler manual and ensuring valves are closed afterwards. If unsure, contact an engineer.

4. Bleed a radiator if you suspect trapped air, then re-check pressure and re-pressurise if needed.

5. If temperatures are very low outside, the boiler may be in frost protection mode (display FP) or the condensate drain may be frozen/blocked; check condensate pipe external runs for ice and thaw carefully. A blocked/flued condensate or flue issue can prevent ignition.

6. Check other gas appliances (hob, gas fire) to confirm gas supply is present. If no gas supply to the property, contact your gas supplier.

When to call a professional:

- If after the checks and a restart the boiler still will not fire and shows other fault codes (L2, F1, F3, etc.).

- If pressure repeatedly drops after topping up (possible leak) or you discover water leaks from the boiler or pipework.

- If you smell gas, see flames, or there is visible damage to the boiler or flue.

- Any internal electrical, gas valve, fan, PCB or thermistor faults, or if the boiler requires internal parts to be replaced.

If in doubt, stop and contact a Gas Safe registered engineer (RGII in Ireland). They can carry out safe diagnostics and repairs. Do not attempt internal repairs on the boiler yourself.