HW OFF in Y-plan system with additional relay?

[Rickenbacker]

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?

 

[matt1e]

There you go
View media item 61942The relay shown is a changeover with 230v coil you will need to use the com and N/C contact connections

Matt

 

[Agile]

Perhaps I am missing something but if the basic problem is the timer does not have an HW on then isn't it easier to fit a new programmer?

 

[dcawkwell]

?
A 3 port valve always give HW. There is no HW off!
As the valve is always open to HW.

Other than when the tank is satified and the central heating is calling
in which case you just get central heating with HW off.

 

[Rickenbacker]

There you go
View media item 45082The relay shown is a changeover with 230v coil you will need to use the com and N/C contact connections

Matt

Any example(s) of a particular item that can be bought from somewhere?

 

[Rickenbacker]

Perhaps I am missing something but if the basic problem is the timer does not have an HW on then isn't it easier to fit a new programmer?

The timer/programmer I've installed DOES have HW on, it doesn't have HW off. I want to be able to only have HT being heated during specific times, not whenever CH is on.

 

[Rickenbacker]

?
A 3 port valve always give HW. There is no HW off!
As the valve is always open to HW.

Other than when the tank is satified and the central heating is calling
in which case you just get central heating with HW off.

I'm new to this, but having pored over wiring diagrams for Y plan, my understanding is that the 3-port valve can be in one of 3 positions, HW only, CH only, both. With a CH on or absent and HW on or absent 'signal' only you can indeed only have the 2 possibilities you describe (which I guess would be HW only or both).

 

[matt1e]

There you go
View media item 45082The relay shown is a changeover with 230v coil you will need to use the com and N/C contact connections

Matt

Any example(s) of a particular item that can be bought from somewhere?

Maplins is probs going to be easier for you

DPDT 240V relay order code JG60Q = £5.49
suitable relay base (to connect your wiring to) order code JG54J = £2.89

 

[matt1e]

?
A 3 port valve always give HW. There is no HW off!
As the valve is always open to HW.

Other than when the tank is satified and the central heating is calling
in which case you just get central heating with HW off

if its correctly wired then no its not "always open to HW"
for example, it's turned off at the programmer (which is what the post is all about )
the second example you have already given

though to be honest, as long as the cyl stat is wired correctly then if you don't want hot water (unlikely) you can just turn said stat down then up again when you do

Matt

 

[dcawkwell]

?
A 3 port valve always give HW. There is no HW off!
As the valve is always open to HW.

Other than when the tank is satified and the central heating is calling
in which case you just get central heating with HW off

if its correctly wired then no its not "always open to HW"
for example, it's turned off at the programmer (which is what the post is all about )
the second example you have already given

though to be honest, as long as the cyl stat is wired correctly then if you don't want hot water (unlikely) you can just turn said stat down then up again when you do

Matt

A 3 port valve is always open to hot water. It is spring loaded
to return to HW. With no HW ON and no CH ON the valve itself
is in the HW position.

There are only 3 positions of the valve are

HW
HW + CH
CH

There is no HW off. The only position where is this true is when set to supply CH only.

 

[matt1e]

There is no HW off. The only position where is this true is when set to supply CH only.

carefully read your above statement.
Is there a hotwater off position or not ????????
yes or no

 

[dcawkwell]

There is no HW off. The only position where is this true is when set to supply CH only.

carefully read your above statement.
Is there a hotwater off position or not ????????
yes or no

Nobody in their right mind would set the CH on to switch the HW off.
Besides the valve cannot work in CH continuously for long periods.

 

[Agile]

The timer/programmer I've installed DOES have HW on, it doesn't have HW off. I want to be able to only have HT being heated during specific times, not whenever CH is on.

It would be unusual for a timer intended for CH and HW to NOT have a HW off contact ( although it might not be specifically marked as that but just shown as a C/O contact.

What is the make and model of your timer?

 

[Rickenbacker]

The timer/programmer I've installed DOES have HW on, it doesn't have HW off. I want to be able to only have HT being heated during specific times, not whenever CH is on.

It would be unusual for a timer intended for CH and HW to NOT have a HW off contact ( although it might not be specifically marked as that but just shown as a C/O contact.

What is the make and model of your timer?

Heatmiser PRT/HW-TS WiFi

 

[leighwont]

There you go
View media item 45082The relay shown is a changeover with 230v coil you will need to use the com and N/C contact connections

Matt

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.