HW OFF in Y-plan system with additional relay?

[D_Hailsham]

I've got a Y-plan system. My room thermostat can call for CH ON or HW ON or obviously both ON at the same time. But it can't call for HW OFF (other than the absence of HW ON).

Is it a thermostat or a programmable thermostat?
If just a thermostat, which timer/programmer do you have?
If a programmable stat, which model?

 

[ianb1469]

Had exactly the same problem and thought this seemed to make sense so I set about wiring it. I noticed that because of the way the MPV works when it is in CH only both the grey and orange wires are live. This means both positions of the cylinder stat have a live going to them and so whatever its status the com is actually live which then flips my relay and removes my hot water off. This drops the valve back towards mid position again closing the switch to orange and with a cold cylinder giving me back my HW off so just creating a loop.

After many silly ideas how to solve this I hit on the obvious, i used the n/o contacts of my second pole of the relay to switch open the wire going to the com of the cylinder stat. This means it is only closed when I have a HW on signal and it's required and blocks off the stray live.

Thought I'd post this in case anyone, like me, found this and had the same problem. Also to offer my thanks to matt for setting me on the right path.

I think that I have the same issue. Would you mind explaining in more detail what you did? I didn't follow that properly. Thanks

Ian

 

[matt1e]

I think that I have the same issue. Would you mind explaining in more detail what you did? I didn't follow that properly. Thanks

Ian

Do you mean how do you connect a relay to give a hot water off connection?

View media item 61942

 

[ianb1469]

I think that I have the same issue. Would you mind explaining in more detail what you did? I didn't follow that properly. Thanks

Ian

Do you mean how do you connect a relay to give a hot water off connection?

View media item 61942

Ah, is that what the previous comment was about. I thought it was something more ingenious. No need for explanation then. Thanks.

As it happens I've just managed to get it working, after a whole bunch of problems: broken room stat, no wire from HW-OFF to MPV (there was actually a spare wire in the wall but not connected at either end) and finally the MPV motor wasn't turning the valve far enough to activate the switch.

This new house I've moved into certainly has lots of awkward niggles so far!

Ian

 

[Norcon]

I've got a Y-plan system. My room thermostat can call for CH ON or HW ON or obviously both ON at the same time. But it can't call for HW OFF (other than the absence of HW ON). Which means that the mid position valve would always be in either the mid-position or CH only position. With the room thermostat came a wiring diagram showing how a relay connected to both live and a cylinder stat could provide a separate HW ON or HW OFF signal.
Any suggestions to What relay could provide this function for me?

Without "HW off" what actually happens is the valve fails to open fully to CH. That occurs via a micro switch making the motor open fully.

You need the grey wire energised either via HW off or cylinder stat satisfied or as matties relay arrangement is showing.

 

[ianb1469]

I've got a Y-plan system. My room thermostat can call for CH ON or HW ON or obviously both ON at the same time. But it can't call for HW OFF (other than the absence of HW ON). Which means that the mid position valve would always be in either the mid-position or CH only position. With the room thermostat came a wiring diagram showing how a relay connected to both live and a cylinder stat could provide a separate HW ON or HW OFF signal.
Any suggestions to What relay could provide this function for me?

Without "HW off" what actually happens is the valve fails to open fully to CH. That occurs via a micro switch making the motor open fully.

You need the grey wire energised either via HW off or cylinder stat satisfied or as matties relay arrangement is showing.

Yes, I got it working now with new HW off wiring in place.

I think that what had happened with the MPV was that since the system had been operating for years without it, the valve was a bit stiff. Removing the controller box and turning it with a spanner a few times loosened it.

Thanks to all for this thread - was really useful to diagnose the unexpected behaviour (i.e. radiators were always warn despite a broken wall thermostat, which was always open circuit).