Old Switchmaster control, no hot water off so..

[75pete]

I'm thinking of having Hive fitted and before I place the order, I'm trying to find out if hive could be fitted as the Switchmaster sm400 appears not to have "Hot water off". This I think is needed for hive to be able to control the hot water cylinder .
Mine is a Y plan
Profile boiler balanced flue
Cylinder with stat
Pump
Switchmaster sm400
Hunnywell 3 port mid position valve
Hunnywell wall room state
So I know I would need the active heating and hot water (2) channel but with no hot water off as an option on the Switchmaster, i would think some wiring mod would be needed.
Im I correct in my thinking, if so, any pointers please.
Thanks, Pete

 

[75pete]

Switchmaster sm400

 

[jackthom]

Is there a main wiring centre where the 3 port valve, boiler, cylinder thermostat, room thermostat etc are all wired together?
It might be best to wire the Hive receiver into that location and abandon the old programmer wiring altogether, unless that cable has an unused wire to use for HW OFF.
Some pictures of the wiring centre will get you more help.

You don't have to operate the system with a HW OFF wire but it would mean that the cylinder would always get reheated when the CH was ON, that's assuming the water wasn't already up to the required temperature.

 

[75pete]

Thanks Jackthom, i would like to have the hot water off, gives me more control. Yes there is a wiring centure, looks a mess. It's next to the cylinder, 3port valve and pump. The wiring on the Switchmaster is x2, 3 core, one is Live, neutral earth, other also 3 core not 4 so no spare cable unfortunately. Your point about getting rid of the Switchmaster wiring altogether and placing the hive receiver next to the cylinder was my think also.The plan would be to get ie British Gas or another in to carry out the work but don't want to order the hive if it a " no go"

 

[jackthom]

You have two Earth connections where really only one is normally required (unless the Earth is being looped through to be used elsewhere) and the Hive Receiver does not even need to be Earthed at all so as long as you can safely identify those two cables in the wiring centre one of the "Earth" wires could be used for the HW OFF.
That is provided they both go to the same Earth connector in the wiring centre, that you can't accidentally mix them up and that the one used for HW OFF is then clearly marked with coloured insulation tape at both ends.

 

[75pete]

Ok, thanks, I will offer that as an idea. So using the earth wire, where would that need to be made off to make the " hot water off" possible in the wiring centure?

 

[jackthom]

If you can identify those two cables ( and maybe some of the others from cylinder stat, boiler etc ) entering the wiring centre in a photo I'm sure someone will help.

 

[75pete]

Ok, will give that a try, thanks again, very much appreciated
Pete

 

[Terrywookfit]

The Y plan will not work properly without water off.

 

[75pete]

The Y plan will not work properly without water off.

That's interesting Terry, I was told years ago that my system was a Y. Only have the single 3 port valve. The hot water is as per the Switchmaster and then satisfied by the cylinder stat.

 

[Echo the husky]

It will function but you will not be able to select heating only, as the hot water off connection is needed to move the valve from the mid position to CH only. The cylinder stat will (should!) have a connection to the HW off on the valve so the cylinder doesn't keep heating when up to temperature if CH and HW are on together.

 

[75pete]

It will function but you will not be able to select heating only, as the hot water off connection is needed to move the valve from the mid position to CH only. The cylinder stat will (should!) have a connection to the HW off on the valve so the cylinder doesn't keep heating when up to temperature if CH and HW are on together.

So, if I get to use one of the earth wires and that sounds possible, where do I make the connection to achieve hot water off in the wiring centure, or is it a bit more then that.

 

[Echo the husky]

You would need to identify that the wire goes to the wiring centre, it will need to be suitably sleeved at both ends to identify it as a live wire, then connected to the HW off wire on the valve (grey wire), leave the cylinder stats HW off connection in place.
The wiring is shown clearly on this diagram:

 

[75pete]

Thanks Echo, the use of the old earth and ensuring its identified at both ends was also pointed out if possible by jack and is a good get out of jail card. I much appreciated the wiring plan you've posted and the connection info needed at the wiring centre/valve.