I wanted to control my central heating from my home automation setup. The first step was to allow X10 on/off control of the central heating on the boiler. Below are the details of how I did this...
I bought an old AM12U appliance module on ebay to modify - this was pretty cheap.
I then opened this up and played around with it a bit trying out a few of the mods here.
I was hoping to get the mod working that would allow it to operate as a high voltage relay, but I can't see how it's really possible as the chip requires feedback from the relay output power to confirm what state it's currently in (I've emailed the original author of this mod but no reply so far). I was able to get it working in momentary operation but that's no good for what I need. So I reset it back to it's original state and confirmed it was still working.
Next I removed the jumper wire on the appliance module board and soldered a push-to-make switch across it. This switch in fact:
http://www.maplin.co.uk/push-to-make-switch-34858
This allows local on/off control of the appliance module.
I snipped the output connections from the appliance module as close to the plug pins as possible and stripped them back. Without these connections the bottom half of the module could be removed. The top half could then be put back together with the snipped wires protruding from the bottom. There were:
Red - Switched live (from the appliance module relay contacts)
Blue - Live (to the appliance module board)
Black - Neutral (to the appliance module board)
Black - Live (to the appliance module relay contacts)
2 wires going to the switch (that I just added)
My boiler (a Worcester Bosch Greenstar 24i junior), and I suspect most others, has a facility for remote switching that would usually be used to wire in to an external device. Inside the electrical connections panel there are two connections labelled 'Lr' and 'Ls' (shown on page 29 of the instruction manual). These are connected by a jumper upon delivery, but the jumper can be replaced by an external switch, or in my case by a relay.
I used this relay:
http://www.maplin.co.uk/30a-spdt-power-relay-37495
in its 240V form.
I then soldered the switched live appliance module output to one side of the new relay input and used a new section of wire to run back to join to the neutral input to the appliance module (I soldered these together for convenience).
I also soldered the blue and black live wires together to make connections easy.
So that I know when the module is on I added a light, this one:
http://www.maplin.co.uk/miniature-round-panel-neon-2010
I soldered connections to it across the new relay terminals, so that the two are in parallel.
I tested this by attaching a temproary power lead and it all worked pretty well, with the new relay switching from the appliance module but its output being electrically isolated from it.
Next I put it all in a box. This box:
http://www.screwfix.com/p/adaptable-box-ip65-110-x-110-x-67mm/17962
To be honest a slightly larger box would have been better, but it just about all squeezed in.
I knocked out two holes for wire access and drilled holes for the button and indicator light. Then I hooked everything up with chocolate blocks inside the box. I split the power lead to the boiler about halfway up and fed it into the box and back out, so that it was still powering the boiler but also the appliance module (in parallel). I also fed in a new length of 2 core flex which I hooked up to the output of the new relay. The other end of this I attached to the boiler Lr and Ls terminals.
So far it seems to be working, although it's early days. Using macros I can now time the heating on and off and also turn it on/off remotely or locally. In the future I might look into adding a temperature sensor to the system.
Obviously I've just described what I've done - I wouldn't recommend that you copy this or use these as instructions in any way as I don't know how it will perform in the long term, but hopefully it will be of interest to someone.
If anyone's wants to know more then please leave me a comment and I might add some pretty photos!
