Boiler displays E09, no heating or hot water, pressure gauge may read zero or very low.

Safety: Only top up the system when the boiler is cool. Over-pressurising can cause leaks.

• Check pressure gauge: If below 1.0 bar, top up using the Thermona filling loop until the recommended pressure is reached (usually 1.2–1.5 bar cold).
• Bleed radiators: After topping up, bleed radiators to remove air and recheck pressure. Top up again if necessary.
• Inspect for leaks: Walk around the property and check radiators, valves, and visible pipework for signs of water leakage. Repair any leaks before repeated topping up.
• Reset boiler: Once pressure is correct and stable, reset the boiler. If E09 persists, the pressure sensor or switch may be faulty.
• Engineer checks: A technician should test the pressure sensor with a multimeter, inspect the sensing tube for blockages, and replace the Thermona pressure sensor if defective.