F10 displayed, furnace does not start, display may show low system pressure

Safety first: Allow the system to cool before adding water. Do not over‑pressurize the system.

• Step 1 – Check pressure gauge: Look at the built‑in pressure gauge or digital reading. Most Protherm hydronic units require around 1.0–1.5 bar when cold.
• Step 2 – Refill system: Locate the filling loop or fill valve. Slowly open it and watch the gauge rise. Close the valve at about 1.2–1.5 bar. Bleed air from radiators if present, then top up again if pressure drops.
• Step 3 – Inspect for leaks: Walk around the system and check radiators, valves, and visible pipes for water leaks. Repair any leaks before repeated refilling.
• Step 4 – Sensor and tube check: If pressure is correct but F10 remains, inspect the pressure sensor and any small tube connecting it to the hydraulic block. Clean or replace the tube if blocked. Reseat the sensor connector.
• Step 5 – Replace sensor if needed: If the sensor does not change reading when pressure changes, replace it with a Protherm‑approved water pressure sensor.