3-way diverter and overrun control

[jashton]

Hi. I have a quick Q re a 3-way diverter, based on Honeywell Y Plan.
I understand the various states the valve can be in and the control outputs.

The only one in question is:
If either CH or DHW (or both) have been on and are turned off then the grey connection becomes live, maintaining the last valve position and providing approx 100V to orange (pump plus boiler).

I'm assuming this is to provide power for overrun. I assume also that 100V is sufficient for the pump as you want to maintain some flow but not full flow as required when the syetem is on.

Assuming I'm correct, what triggers the overrun to stop after x minutes? ie the 100V to orange must be cut at some point or the pump will run constantly. Also, when this cut in power takes place is the grey supply cut also, triggering the valve to return to posn B under spring pressure?

Thanks

Edit. I'm just thinking that power to the pump is controlled via the boiler overrun stat. that would explain how the switching of the 100V is managed.
I assume then that grey remains live constantly while there's no DHW/H demand?

 

[seco services]

the grey becomes live when hw satisfied. this will hold the valve in heating only.
heating won't put power to the grey.
pcb will control the pump overrun
the grey will be live alday long if the hw satisfied.

 

[jashton]

the grey becomes live when hw satisfied. this will hold the valve in heating only.
heating won't put power to the grey.
pcb will control the pump overrun
the grey will be live alday long if the hw satisfied.

Thanks. Makes sense.
Though if hw is satisfied then grey will be live so if heating is on grey will be live. I understand heating won't trigger power to grey but 3-way requires grey plus white to be live in order to siwtch valve to posn A (heating only).

When you refer to PCB do you mean boiler PCB or CH controller?

 

[seco services]

yes and yes the boiler pcb.

 

[gas4you]

Pump over run is 99% of the time controlled by boiler pcb.

This is why boilers have a permanent and switched live (from the heating controls) to them.

 

[D_Hailsham]

If either CH or DHW (or both) have been on and are turned off then the grey connection becomes live, maintaining the last valve position and providing approx 100V to orange (pump plus boiler).

The fact that there is a voltage on the orange wire when heat has been satisfied is a quirk of the system. If the voltage was not reduced, the pump (and boiler) would run. By reducing the voltage to 100, which is less than the pump and gas valve need to operate (230v), the boiler stays off.

I'm just thinking that power to the pump is controlled via the boiler overrun stat. that would explain how the switching of the 100V is managed.

Boilers with a pump overrun always have a permanent mains connection. The over run is either controlled by a thermostat or by a timer.

I assume then that grey remains live constantly while there's no DHW/H demand?

The only time the grey is live is when either the cylinder stat is satisfied or the HW has been turned OFF at the programmer.