replacing a switchmaster 805 (wiring problem)

[Sanshinman]

Hi all,

I'm changing my Switchmaster 805 controller as it's not worked in years and I've finally got sick of using alternatives to having the system work properly!

Problem: lack of CH off signal wire.

The Horstmann CetaurPlus 27 programer has very use change over guide to the wiring but I have an issue of missing a wire.

There is no heating off wire back to the switchmaster and I have no idea where I need to pick this up from in the wiring centre.

I have a hot water off signal which unless its the return from the thermostat I would imagine is redundent? but obviously I don't want to mess about with it without some guidence.

The system:

The Boiler is an Ideal (E Type) relic but still working so what the hey!
The pump is a grunfoss I replaced a few years back:
The 3 Port is a defuncted Satchwell DM5601 I am waiting for a replacement actuator for as we speak (it's still wired, it's just the nylon/ plastic hub that's fractured)
The room stat is a 3 wire Satchwell dial.


I believe as the pump is before the 3 port feed from the boiler it is a W plan open vented, fully pumped system?

The issue here is I can only have hot water or heating never both together so I need to have the timings set up so as not to clash as even if the tank stat is satisfied if HW is 'on' the valve will not motor over to heating.

I can work around this, we don't use a lot of DHW but alternatively should I consider adding in a mid position valve?

I would like to fully automate the system so unless one of you knows where I can pick the signal up from would the alternative be to install a programable room stat? if so can one be recomended.

Cheers,

Trevor.

 

[Whitespirit66]

I hope I have understood your post correctly.

If you are wiring a programmer for W plan, you don't wire in any 'off' wires. There should only be ch on, and hw on.

If you were wiring for Y plan, you don't normally have ch off. It's hw on, hw off, and ch on.

The 2 channel programmer is what you need, not a programmable room stat, as this will only control your heating.

Y plan is always preferable to W plan.

 

[Sanshinman]

I hope I have understood your post correctly.

If you are wiring a programmer for W plan, you don't wire in any 'off' wires. There should only be ch on, and hw on.

If you were wiring for Y plan, you don't normally have ch off. It's hw on, hw off, and ch on.

The 2 channel programmer is what you need, not a programmable room stat, as this will only control your heating.

Y plan is always preferable to W plan.

I apreciate the responce and think you got it, it is wired as you suggest for a Y plan, so I'll assume the valve in there is capable of being in this configuration, cant really tell until it works as it's not worked for so long I can't remember - new actuator is being ordered tmrw.... thought it was a W though

I can see the logic in what you are saying too but the issue is I can't turn the heating off, if I wind up the room stat it comes on no mater what the programer says, what I want to be able to do is time the heating on and off leaving the thermostat set rather than having to keep wining this back to turn the heating off.

Dont know if you knwo the particular valve in quesiton but it is a full rotation power on/ power off valve rather than a spring return valve so this could change things??

 

[Whitespirit66]

Sounds like something isn't wired correctly. When the programmer turns the heating on, the ch on terminal on programmer becomes live. Power goes from this terminal to the room stat, and if calling for heat, should allow current to go to the valve.

However, I have no experience of momo valves, so I will have to let someone more knowlegeable on these step in.

 

[matt1e]

I think the older sachwell momo actuators did req a CH off signal but the newer momos can be wired as per spring return ie no ch off req (at least i know they definatly do a momo that can be wired as such)
I'd wait to see what is req when your new actuator turns up

if it reqs a ch off then you will have to add an extra cable core or fit a relay to provide a signal
or fit a valve that doesn't req a ch off

Matt