How to Fix / Troubleshooting

Safety first: Isolate power and allow the unit to cool. Close water valves before opening any hydraulic components.

Steps:

Check water pressure: Ensure inlet pressure is within Saunier Duval specifications. Open all isolation valves fully.
Bleed air: On models with an internal pump, use the bleed screw on the pump or automatic air vent to remove trapped air.
Free the pump: Remove the pump front screw (if accessible) and gently turn the rotor with a screwdriver to free it if stuck.
Descale: If flow is poor and the unit overheats quickly, the primary heat exchanger may be scaled and require professional chemical descaling.

Warning: Hot water and steam can escape when opening bleed points. Wear gloves and eye protection.

F12 appears intermittently, especially during high demand, unit shuts down

Possible Causes