Boiler shows A17, pump runs but burner does not start, system may be cold

Safety: Allow the system to cool before refilling. Do not over-pressurise.

• Check pressure gauge: If below the recommended cold pressure (typically 1.0–1.5 bar), open the filling loop and slowly refill until the correct pressure is reached, then close the valves.
• Bleed air: Bleed radiators and the boiler's automatic air vent to remove trapped air.
• Inspect for leaks: Look around radiators, valves, and under the Herz boiler for signs of water leakage.
• Check pressure sensor: If pressure is correct but A17 remains, the Herz pressure sensor may be faulty and require replacement.