Please help us get to the bottom of Boiler/CH/HW not working!

[MKB13]

Hi all, really at a loss after months of back and forth on this, would appreciate any direction.
Have a reasonable old glow worm flexicon 24hx condensing boiler.
I’ve had new pipe work run and a pressurised cylinder installed.
Heating thermostat was older than I was so decided to switch to a hive heating and hot water system, my naivety meant I bought the system that my electrician suggested, without realising I had purchased the ‘heating’ Hive, not the CH and HW one, which I have since learned should be the correct one as I don’t have a combi boiler.
Anyway I was assured that this CH hive can still work in tandem with a separate HW control unit which is more old school and manual setting of schedules etc.
However when either the Hw or CH is about to start its schedule, the boiler without fail kicks out in an f22 fault. If I then reset boiler once the Hive or HW control are now on, then the boiler remains on until the schedule is set to turn off, and then the boiler kicks out a fault again.
If the CH or HW is on constant together or either one on its own and I’ve manually turned it on, the boiler works fine.
Does anyone know what could be the issue, is there a signalling issue possibly from the two different controls working against each other?
Or something wrong with the PCB, or maybe that I need to repressurize the system and bleed it all out? My plumber thinks it’s a leccy issue and vice versa! Just panicking as have a baby due in the next few weeks so imperative to have heating and hot water!

Thank you!

 

[ericmark]

Pure guess, and I am an electrician not a plumber, but a motorised valve should open when it gets a command signal from the thermostats, and then when open, it activates a micro switch that runs boiler, so the valve is open before the boiler fires, if wired so that the thermostat goes direct to the boiler, than boiler and pump will start before the valve has had time to open.

However there are different systems (Plans) C, Y, and S are the common ones, with C and Y there is always a route for water to flow, only S plan has no route if valve has failed to open.

 

[MKB13]

Sorry should have mentioned that there is a motorised valve for both HW and CH, and a pump

 

[Madrab]

F22 a is low pressure code (not a flow error) on the GW's. Can that be caused by an electrical fault, can't say I've ever heard of that but never say never. That being said the HX's could be run as open vent so not sure it would actually have a pressure sensor, would need to check. Is it open vent or sealed?

If an external electrical fault is suspected then time to take the controls out of the equation and see if the boiler runs fine directly. Isolate the boiler, remove the switched live(s) (SL) on R and link 240V across, switch back on and see if it runs. If no error then time to work back through the controls, all the controls should feed back to the SL (orange from the zone valve) in the wiring centre and ensure the boiler supplies the pump.