F10 displayed and the softener reports high internal pressure or shuts down unexpectedly

Safety: High water pressure can be dangerous. If you suspect overpressure, close the main stopcock and relieve pressure at a tap before working on the system.

Steps:

• Measure mains pressure: Use a pressure gauge on a nearby tap. If pressure exceeds the Vaillant specification, install or adjust a pressure reducing valve upstream of the softener.
• Check outlet valves: Ensure that any outlet or bypass valves downstream of the softener are fully open and that no service valves have been left closed.
• Inspect internal strainers: Some Vaillant heads include fine strainers on inlet/outlet ports. Isolate the unit, relieve pressure, remove strainers, and clean them under running water.
• Check pressure sensor: If fitted, inspect the pressure sensor connection for leaks or damage. Replace the sensor if it shows signs of water ingress or corrosion.
• Reset and monitor: After correcting pressure and cleaning strainers, clear the F10 code and monitor operation over several days.