Any Worcester-Bosch Guru?

[rtcosic]

2001 Worcester-Bosch Greenstar 18i System Boiler.
It has power at the CU.
If I turn the local isolator off and back on I hear a brief whirring noise so it seems there is power to the boiler.
But no blue light and it doesn't talk to the controller.

Any obvious checks I can make before delving deeper or - look away now - paying for help?

 

[voipio]

Is the boiler flow temperature control set to a reasonable value (suggest at least midway)? Does the controller power up, and does its output signal go high when it should? Does the room/hall thermostat(s) work, and send a demand signal to the boiler?

 

[rtcosic]

Is the boiler flow temperature control set to a reasonable value (suggest at least midway)? Does the controller power up, and does its output signal go high when it should? Does the room/hall thermostat(s) work, and send a demand signal to the boiler?

50 deg C. Currently showing 21 deg C which is in itself a little odd.
Heatmiser control system operates all the other outputs correctly. I haven't probed the wiring centre.

My memory tells me the blue light is on whenever the power supply to the boiler is on irrespective of a demand signal from the controller.

 

[voipio]

Is the central heating loop pressure OK?

 

[rtcosic]

Is the central heating loop pressure OK?

Boiler and filling loop pressure both c. 1.2 bar.

I have just pressed the spanner button and cycled through the codes again:

i1 203 System Standby
i2 356 Low Mains Voltage F0 (or may be FO)
i4 Max DHW Output 18.0
i8 Ionisation Current (MA) 0.0
i9 Flow Temperature 20 deg C
i20 CU Version 1.4
i21 HMI Version 1.4
i22 HCM 1432 Version 5

Mrs Google suggests the F0 fault is a generic failure code so I think I have reached the limit of my diagnostic skills.