Error 10; unit will not start and may show no fan or ignition sequence.

Safety: Allow the system to cool before topping up pressure. Hot water can cause scalding.

Steps:

• Check pressure gauge: Look at the system pressure gauge. If it is below the recommended cold pressure (often around 1.0 bar), the heater will lock out.
• Top up via filling loop: Open the filling loop valves slowly and watch the gauge rise. Close the valves when the correct pressure is reached. Do not overfill.
• Bleed air: Bleed radiators or high points and recheck pressure, topping up again if necessary.
• Inspect for leaks: Check visible pipework, radiators, and the underside of the heater for signs of water. Persistent pressure loss indicates a leak that must be repaired.

Note: If pressure is correct but error 10 remains, the water pressure sensor or switch may be faulty and require replacement.