Megaflo wiring centre

[mdrandall]

With a view to fitting a NEST Heatlink for the upstairs zone I had a quick look at the Megaflo wiring centre but something is confusing me.

When I manually open the Honeywell zone valve using the lever on the side there is no response from the boiler/pump. In fact if I try the downstairs zone valve or even the HW valve nothing happens either. However, the system works correctly. Checking the voltage in the wiring centre there is no permanent live to terminals 1 to 4. However, with the valve lever in the normal auto position, if I increase the temperature demand on the TP4000 thermostat the valve opens and live is connected to 1 to 4 (and of course to the pump and boiler demand terminals.

Is there an alternative way of connecting the wiring centre which differs from the Megaflo installation guide such that the wiring centre live is supplied on demand by the TP9000/TP4000 ? I've Googled but all the airing diagrams show a permanent live.

 

[oldbuffer]

The manual lever on the Honeywell valves (and most others) does not move the gears in the head far enough to actuate the micro-switch which fires the boiler, only enough to open the valve.

 

[mdrandall]

Ah, that makes sense. I still don't understand why the Megaflo wiring centre does not have a permanent live. The grey wire to the valve is not live until the programmer / thermostat calls for heat via the brown wire.

 

[SavageW]

Who ever wired it could've used the orange as the permanent live an grey as switch live (why your getting live at grey once you've created a demand) it doesn't really matter if you use grey as permanent live or orange it's just a switch.

 

[hertsboilers]

For most two port valves like Honeywell 4043 etc, the grey can also be joint with brown to a switched live.

 

[picasso]

For most two port valves like Honeywell 4043 etc, the grey can also be joint with brown to a switched live.

Not on an s plan you cant

 

[mdrandall]

Definitely S plan as there are three separate water circuits each with its own valve. I can only think that a permanent live goes to the thermostat and becomes switched on call. This is then connected to both the valve grey but also to the wiring centre live terminals (and hence the valve brown, pump, boiler etc). Seems on odd way of doing it though.

 

[hertsboilers]

Not on an s plan you cant

I thanked you this afternoon, but after had a re-think, I stand by my original saying, ie, the grey and brown of Honeywell 4043 on S plan can joint together to the switched live.

 

[Dan Robinson]

It can work as Ming says...


Ad for the sake of one-up-man-ship...The OP has an S Plan Plus.

 

[Dan Robinson]

And for two-up-man-ship...

Some wire the orange as P/L as it is COM on the V4043H1106 and V4043H1080 versions.

 

[picasso]

I thanked you this afternoon, but after had a re-think, I stand by my original saying, ie, the grey and brown of Honeywell 4043 on S plan can joint together to the switched live.

Course it will work .......until one of the valves latch

 

[mdrandall]

Thanks for all your comments. I'll investigate further tomorrow to try and work out where the live comes from. Assuming the live is routed through the relevant thermostat, I'll just trace the wires and wire the Nest Heatlink in its place.

It would be more straight forward if the installer had followed the Megaflo recommended wiring and used a permanent live to terminals 1 to 4. Out of curiousity, I'd like to know why it was done this way as there is no shortage of wires coming in/out the wiring centre. There doesn't seem any advantage and just confuses.

 

[Dan Robinson]

A lot of these things were done by house bashing sparks (it sounds like you have a relatively new build house). At the best of times electricians struggle with heating controls... Stick another zone valve in the mix and they're usually fecked.

Mind you - some of the efforts of plumbers leaves a lot to be desired with basic heating wiring too.

 

[mdrandall]

You are correct in that the house is a new build, about a year old. I still can't work out why the Magflo wiring centre does not have a permanent live. There is a another wiring box on the wall of the airing cupboard so I will have to trace through the wires in there as well.