Furnace shows low water pressure or water pressure switch fault, will not fire

Safety: Allow the system to cool before repressurising to avoid scalding.

• Check pressure gauge: On Baxi sealed systems, verify the gauge reads at least the minimum required (often around 1.0 bar cold). If low, use the filling loop to slowly add water until the correct pressure is reached.
• Bleed air: After filling, bleed radiators and top up pressure again if needed.
• Inspect for leaks: Walk the system and check radiators, valves, and visible pipework for signs of water leakage. Repair any leaks found.
• Test pressure sensor: If pressure is correct but the error persists, check the wiring to the Baxi water pressure sensor or switch. Replace the sensor if it is not responding correctly.

Note: If pressure drops repeatedly, the expansion vessel may be flat or ruptured and should be checked by a heating engineer.