Just a quick note to let everyone interested know that I was able to wire my "smart" controls for hot water and heating in parallel with my "dumb" controller. My setup is as follows:
1) Z-Wave Secure (also known as Horstmann) Wall Thermostat & Receiver Set (HRT4-ZW + ASR-ZW) for heating
2) Z-Wave Secure (also known as Horstmann) Boiler Receiver (ASR-ZW) for hot water
I had these installed when I changed my boiler. As with everything I automate in the house I try to leave a non-smart/analog route in case my home automation system fails. So when my plumber installed the new boiler he fitted a new Honeywell ST9400C 7 day "dumb" controller. In a typical installation the switched live cable for the heating starts off the 7 day programmer, then it goes to the thermostat receiver (in my case number 1 above) and then to the boiler switch return, so basically in serial. The idea is that if the 7 day programmer is in the "On" for heating then the cable going to the thermostat receiver is "live". Then if the thermostat is below the set temperature it will also turn on which will then turn on the boiler. In effect you need to have both the programmer and the thermostat On for the boiler to go On. This makes sense in that kind of "analog" setup but in my case I wanted to have them in parallel not in serial. Why? Because I am controlling both my hot water and my heating with "smart" schedules from Indigo based on various factors so having the 7 day programmer getting in the way of that was a not an option. I explained how to do the parallel installation to the plumber but he wouldn't get it so I told him to do it in the standard way. This meant that for my Secure receivers to work for heating and hot water I had to set the 7 day programmer to be On continuously for heating and hot water, in effect turning the 7 day programmer in a "dumb" constant live feed. I didn't need to have a schedule in the 7 day programmer since I could turn 1) and 2) above with schedules from Indigo. It also meant that should my Secure receivers fail for any reason then I would have no heating or hot water since the Secure receivers were at the end of the chain.
So I went ahead and change the wiring to be in parallel. The wiring is pretty simple actually. Previously I had something like this:
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7 day programmer => Switched Live for Hot Water => Hot Water Secure Receiver => Boiler switch return for hot water
7 day programmer => Switched Live for Heating => Hot Water Secure Receiver => Boiler switch return for heating
Which I then wired like this:
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7 day programmer => Switched Live for Hot Water => Boiler switch return for hot water
Hot Water Secure Receiver =^
7 day programmer => Switched Live for Heating => Boiler switch return for heating
Hot Water Secure Receiver =^
So now my 7 programmer can switch the boiler for heating or hot water normally. My Z-Wave receivers can also do it as well. The big advantage of this setup is that I can now operate in "back up" mode with the 7 programmer should anything happen to my Z-wave receiver or Indigo. In a normal operation though my "dumb" will be set to heating and hot water Off all the time, since I control the heating and hot water using the Secure receivers and my Indigo schedules. It also means that any plumber coming to my house to look at my boiler doesn't need a manual to understand how do my controls work. They can simply use the 7 day programmer as they would in any other house and the boiler will respond as expected. It also means that should I ever sell the house I can take my Z-Wave receivers away without major wiring issues. I could literally cut all the cables going to the wiring box and everything will still continue to work normally with the 7 day programmer.
Hope it helps someone else.
Thanks