Mid Position Valve Programmer

[John.g]

I've often seen this wiring diagram for Y plan but is the cylinder stat wired correctly?, should the cylinderstat terminal1 go to the boiler+circpump, terminal2 to the MPV grey wire and terminalC to (from) the programmer "HW OFF"?.
The below wiring suggests to me that with "HW Off" and with the cylinder stat satisfied that there is still power to the boiler+circpump.

 

[SJB060685]

That is wired wrong yes. C or common should be fed from HW on.

 

[ShaunCorbs]

It’s doesn’t matter it’s a switch so not polarity sensitive

 

[SJB060685]

It’s doesn’t matter it’s a switch so not polarity sensitive

I agree but look at the wiring mate. From what I see when the HW is off at the programmer and the cylinder stat is satisfied your still seeing a live to the boiler and pump.

 

[John.g]

If HW is selected off, I presume "HW Off" is live, if the cylinder stat is satisfied, will it not keep the boiler+circ pump running via WC terminal7+cylinderstat terminal2+cylinderstat terminalC+WC8?.

 

[exedon2]

John if you look for Honeywell home wireing diagrams there is a app you can download to your phone/tablet with all the wireing diagrams on.

 

[John.g]

IS this correct???.

 

[SJB060685]

That is correct yes. As mentioned above there’s a Honeywell app you can download with all the common wiring diagrams, Y plan, S plan, W plan , C plan etc. of course this app doesn’t have schematics for custom wiring one might occasionally have to design.

 

[John.g]

As a aside, if someone ever wondered, like I often did, why a MPV can't be made to stall in mid position with a reduced AC voltage instead of converting AC to DC, the answer is it doesn't stall in mid position, it is held in position by an electrical brake.

"DC will hold them in position without any spring. The position of rest is set according to when the DC is applied.
If you visualise a permanent magnet inside a winding, no comutator, you have a synchronous motor.
The permanent magnet will follow the AC magnetic field as it reverses, in sync with it, with the permanent magnet rotor N pole following the winding S pole as it swaps from one side to the other.
(and vice versa)
Apply a DC current, you now have a winding with N/S poles fixed, and a permanent magnet with fixed N/S poles. The rotor will stay fixed with its N pole at the winding S pole, going nowhere."

 

[SJB060685]

And that is exactly why the diode is used.