Boost Switch to Replace Programmer - Help

[jayb125]

Hi All,

My father is getting older and I want to replace the heating controls with something simpler - also relocate it to a position easier for him to get to.

I have got some 2hr boost switches (here) - one for Heating and one for Hot water. From what I can tell the system is currently wired as an Y-Plan system. It has a Honeywell wiring system. Here is a diagram of how it currently is:

and this is how I am going to wire it up. But am confused about the 3rd wire from the 'cylinder stat -- to the programmer'. Where is this 3rd wire supposed to go? to the cylinder stat - (2)?

Any help is much appreciated.

Many Thanks, J

 

[RandomGrinch]

Hi,

I'm only a DIY'er, so you may wish to wait for a second opinion!

The boost timers you have bought are SPST (Single Pole Single Throw) relays. Whereas your ST6400C had a SPDT (Single Pole Double Throw) relay to provide live power to H/W on/off as appropriate.

The simplest solution I can think of, is to retain the ST6400C and it's wiring for the hot water circuit. Set it for continuous hot water and power it through your new boost switch.

If this behaves as a normal relay (and here I may be wrong!), then the live will still be fed to H/W off, with the power off to the programmer.
When the boost switch is operated, the controller is turned on (and when set to continuous), the relay should click over to provide live to the H/W on.

I hope that makes sense!

EDIT:
AHH, sorry, that wouldn't work
The live to the outputs is internally fed from the programmer. Without power to the programmer there would still be no power to the H/W off, without some internal modifications; and that wouldn't be good practice.