I have a Glow worm Flexicom 30cx that displays the F9 fault when switched on with no hot water / heating demands. It makes a few clicking noises but faults out after about 30 seconds .The manual says the pressure sensor or wiring or pump is seized. The pressure sensor reading is OK and varies if water is drained, flashing and disabling below 0.5 bar but ok at above. The pump is not seized. Can anyone help before I start replacing parts-- Thanks