why is my jaguar boiler showing FO on the display panel?

Extract from the Jag 23 / 28 Kw boiler manual

Diagnostic error messages
In the event of a fault the following diagnostic error messages will be displayed:
Message Fault Action Comments
F0 Loss of system water Refill system Pump runs for one
Check for leaks minute.
Boiler is restarted by
switching of main
switch.
Air lock in boiler Bleed boiler and system
Pressure sensor failure Check the pressure sensor
(Sensing inlet must not be clogged)
F1 No flame detected Check flame sense electrode
and connecting cable
Check ignition electrode
Check ignition unit on gas valve
Check fan operation
Overheating of the boiler Reset overheat thermostats If overheat Thermo-
Check the pump revolution stats are blocked,
boiler does not ignite
when starting
F2 Central heating thermistor Check if flow thermistor is not
failure disconnected or short-circuited
Sensor Ohm resistance
10 kΩ by 25°C, 12,7 kΩ by 20°C,
16 kΩ by 15°C
2000225078 42
CH water temperature Check if system is not frozen
below 3°C
F3 Heat exchanger blockage Check main heat exchanger Boiler shuts down and
Check domestic heat pump runs
exchanger
F4 Domestic hot water Check thermistor/leads Domestic hot water is
thermistor faulty Sensor Ohm resistance: available bur poor
10 kΩ by 25°C
12,7 kΩ by 20°C
16 kΩ by 15°C
Air pressure switch failure:
If the fan and the pump is running but the boiler doesn’t light, check the air pressure
switch.
Blown fuses:
If the main switch is on and display does not light check the FUSE (1) T80mA, see
diagram 22.
If the display lights but the pump, the fan and the ignition module don’t work check the
FUSE (2) T1.6A, see diagram 22.
Warning message:
If the pressure in CH system drops to 0.8 bar the LED on the Bar/MODE button starts to
flash. This give you information that CH pressure is on the low limit and must be pressurised.
Nevertheless the boiler works until the pressure drops to 0.6 bar – then boiler
shuts down and F0 is displayed.
DHW flow is poor
If DHW floor is poor or boiler does not start when hot water tap is open, check following:
Cold water supply pressure is at least 1 bar.
Check if the cold water filter or flow regulator (plastic ‘O’ ring) is not clogged.

tom
March 2010