Three port valve and John Wards video some thing seems wrong?

[ericmark]

The grey wire is energised when DHW is NOT required,

comes from the normally closed contact, both on the tank thermostat and the programmer. So when the DHW only is required there is no power to the valve, and the boiler is supplied from terminal 1 (N/O) from the tank thermostat. If then CH is required, the white wire is made live, so until SW1 changes over it motors the the valve, at which point the diode and resistor matrix will hold it in the central position. If DHW is no longer required then the grey becomes live and the valve will now motor all the way across, and SW2 will power the boiler, if the white wire looses power the valve will remain all the way across, but there will be no power to the orange wire so boiler will stop. If now DHW is required the power to grey is lost, so the valve will now return to rest so DHW only.

This does not seem to be what the video is saying. So who has it wrong, me or John?

I was trying to explain why when SW1 sticks in moving the bleed leaver to the bleeding position can keep the central heating working, however neither mine nor Johns explanation seems to ring true, so maybe @flameport can answer why latching the bleed lever can keep the system running when the micro switch sticks?

Only out of interest as my heating is C Plan, but just can't get my head around how it works.

 

[SUNRAY]

Sorry Eric 20 minutes of his waffle has become more than I can bother with.
I think I still have a redundant valve in my 'Gas fittings etc' box, it should be quicker to inspect and work out for myself.

 

[flameport]

With the valve in the manual mid position, the heating will 'work' because the valve is open, water flows to both ports.
Boiler can be activated by selecting hot water, which is not switched via the valve.

 

[ericmark]

With the valve in the manual mid position, the heating will 'work' because the valve is open, water flows to both ports.
Boiler can be activated by selecting hot water, which is not switched via the valve.

I know with a faulty micro switch (stuck in) when hot water is called for heating also works, but also when hot water is not called for when latched the heating will work, however in the summer the radiators get warm when hot water called for.

So when hot water not called for SW1 when latched means valve will go all the way over as grey is line when hot water not called for, so that means SW2 will be made, so when ever white is made live the central heating will run.

It seems I made a mistake, on rewatching the video I realised I have made an error. It now makes sense to me, thank you.