Boiler displays E10: low water pressure or water shortage, preventing the boiler from firing.

Safety first: Allow the system to cool before topping up. Do not over-pressurise.

• Check pressure gauge: Read the boiler pressure gauge. If the pressure is below the recommended cold pressure (typically 1.0–1.5 bar), the system needs topping up.
• Top up via filling loop: Locate the filling loop (flexible hose with two valves). Open both valves slowly until the gauge reaches the correct pressure, then close both valves tightly.
• Bleed radiators: Bleed air from the highest radiators using a bleed key. Recheck and adjust the system pressure as needed.
• Inspect for leaks: Walk around the system, looking for damp patches, dripping valves, or discharge from the safety valve pipe. Repair any leaks before repeatedly topping up the system.
• Check pressure sensor: If the gauge shows correct pressure but E10 persists, the electronic pressure sensor may be faulty and require replacement.

When to call a professional: Persistent pressure loss, visible leaks, or replacement of the pressure sensor should be handled by a heating engineer.