Error E109

Safety precautions:

1. If you smell gas, treat it as an emergency: do not operate any switches, leave the property immediately, ventilate if safe, and call the gas emergency number.

2. Switch off the boiler and isolate electrical supply before touching any internal parts or removing any covers. Do not attempt internal repairs unless you are a qualified engineer.

3. Wear eye protection and use a cloth or small container when bleeding radiators to catch water.

Initial homeowner checks you can do safely:

1. Check the boiler display and note the fault code and any additional messages. Try a single reset first: press and hold the reset button (or selector) for 5-10 seconds and allow the boiler to attempt restart. Do not keep repeatedly resetting if it returns quickly.

2. Check the system pressure on the boiler gauge. Target pressure is typically around 1 to 1.5 bar when cold. If pressure is below about 0.5 bar (or below your manual's minimum), topping up is likely required.

3. Top up the system pressure using the filling loop if you are confident doing this: with the boiler switched off, open the filling loop valves slowly until the pressure reaches about 1–1.5 bar then close the valves tightly. Consult your boiler manual if unsure.

4. Bleed radiators to remove trapped air: turn the heating off and let the system cool, open radiator bleed valves one at a time until water runs steadily, then close. Re-check system pressure and repressurise if it drops.

5. Check for obvious signs of leaks around pipes, valves and the boiler. Look at any automatic air vents at high points; if closed or blocked, bleed them or call an engineer.

6. Check that the isolating valves under the boiler (flow, return, cold, gas isolator) are in the correct open position. Do not turn the gas valve on or off unless you know what you are doing.

7. Listen for the central heating pump when the boiler tries to call for heat. A quiet or non-spinning pump or grinding noise can indicate a seized or failed pump.

If the fault remains after the homeowner checks:

1. Do not continue to reset the boiler repeatedly. If E109 returns, power down and call a Gas Safe qualified engineer.

2. What the engineer will typically check and do: verify correct system pressure and gauge accuracy; test the pre-circulation and main pumps for electrical supply, rotation and speed; check motorised valves and check that flow/return sensors and pressure/flow switches are working; inspect for sludge, debris or blockages and advise a system flush or powerflush if needed; check and clear any automatic air vents; inspect wiring, connectors and the PCB for faults; replace faulty pumps, sensors, valves or components as required and then commission the boiler.

Final notes:

- If you are unsure at any stage, or if the fault involves gas, internal wiring, the pump or removing the boiler casing, stop and call a Gas Safe engineer.

- Repeated low pressure or recurring circulation faults usually indicate a deeper issue (leak, faulty expansion vessel, seized pump or heavy sludge) that requires professional diagnosis and repair.