No 'HW off wire' - why not?

[sparkol]

I haven't done much with heating systems before so please go easy.

Y-plan system. I want to replace a two-channel programmer (replacing Danfoss 102 with a Drayton LP522).

The existing programmer has terminals for 'HW on' and for 'CH on' but it doesn't have a terminal for 'HW off'. I thought a Y-plan system normally had a wire for 'HW off' which is live when the cylinder stat is satisfied.

Looking at the wiring diagram for the programmer I'm proposing to fit, it suggests that on a Y-plan system there should be a 'HW off' wire running back to the programmer, to tell it when the cylinder stat is satisfied.

Am I ok to simply transpose the connections from the existing Danfoss programmer (i.e. L, N, E, CH on and HW on) to the new programmer. In other words, do I need to worry about the fact there is currently no wire for 'HW off' at the programmer?

What I don't get is why you would ever have a 'HW off' connection at the programmer anyway - I would have thought that when the programmer stops calling for hot water it will simply turn off the switched live to the cylinder stat which will therefore turn of the switched live to the pump and boiler. As long as there is a 'cylinder stat satisfied' wire between the cylinder stat and the mid-position valve to tell the valve which way to point then won't that suffice?

Please enlighten me! Thank you!

 

[Doomed]

You sure its a y plan? not a W plan with a diverter valve rather then a 3 port valve?
look at these:
http://www.timstephenson.me.uk/files/2012/01/sundial_complete.pdf

 

[onions1066]

You wouldn't be able to run a y plan on a 102. Normally pump feed into ch on boiler feed into hw on. These systems normally use a summer valve or 2 port. Have you checked the airing cupboard?

 

[sparkol]

Haven't checked the airing cupboard, but will do.
Thanks for the link to the wiring diagrams.

In the meantime, can I replace the Danfoss 102 with the Drayton LP522 and just transpose the terminals?

Thanks

 

[onions1066]

The timer you are trying to fit will control heating and hot water separately the 102timer your replacing wont you will either have heating and hot water or hot water only. Some timers will have the option to change on the back of the controller so when you put the hot water on it will put the heating on as well the controller you've got I'm not sure without looking. I know the Siemens controller will have that option.

 

[D Skelton]

Hot water priority system mate

 

[sparkol]

The timer you are trying to fit will control heating and hot water separately the 102timer your replacing wont you will either have heating and hot water or hot water only. Some timers will have the option to change on the back of the controller so when you put the hot water on it will put the heating on as well the controller you've got I'm not sure without looking. I know the Siemens controller will have that option.

Yes, this timer has a setting for gravity-fed systems, which it says does not allow indepedent setting of heating without hot water. So, I can put the timer on this setting and just transpose the wires?

 

[onions1066]

Yes, this timer has a setting for gravity-fed systems, which it says does not allow indepedent setting of heating without hot water. So, I can put the timer on this setting and just transpose the wires?

If that's what it says yes you can

 

[BoredSparky]

When the cylinder thermostat is satisfied, the contact will change over from cold to hot and the system will shut down. The live now presented on '7' will be used in the situation that both CH and HW are on and the cylinder thermostat is satisfied. The live from '7' feeds into the valve via the grey wire and causes it to take up position A when a signal is also present on the white.

 

[BoredSparky]

Not my words above, pulled it from some blurb on Honeywell site, basically the H/W off terminal will put 240v on to the grey wire on the 3 port which along with the 240 on the white wire will power the valve into the heating only position.

 

[onions1066]

The chance is there won't be a motorised just a summer valve