DIY Heating Interface – Review

Submission by Steve Jones – I wanted to improve the control of my central heating system by utilising my home automation controller (HomeVisionPro) whilst still retaining the original central heating timer so it could easily be switched back on if the controller was down or if I needed to take HV out if we moved.

Having removed the timer from its wall plate it became evident that there was a useful wiring diagram on the back which made this project easy to implement. The diagram showed the timer is just two time controlled relays. One for hot water and one for central heating.

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I decided the best thing to do was make a small module on some PCB strip board containing two relays to switch the mains current for both HW and CH. The 12volt DC coils will be switched on demand from HomeVisionPro… The fuse holder is for a 200ma fuse for the coils 12v supply… For added safety I put the 50mm x 50mm PCB in a potting box purchased from Maplins and potted the board in potting resin…

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Next job was to chase in 35mm deep single gang wall box next to the existing timer for the module to sit in the back with a status/override switch on the front.

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Using a modular Clipsal switch I decided I wanted two push buttons to signal HV so I could override the setting of HW and CH (i.e. toggle them on or off). I also added an on/off switch to isolate the 12v supply to the coils thus providing a local means of disabling HV’s control… I added two neon’s red for HW and green for CH… These were wired direct to terminals 3 and 4 respectfully together with a neutral. In wiring it this way if either the controller or the timer switches HW or CH on the neon’s illuminate. To make it look the part I got a local engraving shop to add the decals for £8.00

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Wiring
I wired the yellow (CH) and the Blue (WH) from the module’s relay contacts to terminals 3 & 4 so putting the relay contacts in parallel with the existing timer, The other side of the contacts go to 240Vac positive. The two 12Vdc coils are wired back to the A ports (relay ports) of HomeVisionPro which supply the 12v supply on demand. The water and heating (momentary push) switches are also wired back to HV and are connected to two input ports with a simple bit of code to toggle the supply to the coils thus switching the boiler on and off (i.e. on push of switch, if boiler on switch it off. If boiler off switch it on….) The off/Auto switch is there to isolate the coils supply in the event the timer is required again.

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Control – The standard boiler timer in now left switched off and I use HomeVisionPro to control the boiler. With HV this also has the ability to allow control remotely by other means i.e. IR, RF, the internet, mobile phones ect…. The next job for me is to link up my intruder alarm to signal HV when we are out the boiler can then be switched off automatically if the outside temperature is above a given temperature.

I hope this maybe of use to some one out there.

Steve.

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Parts Used

2 x 12V/12A Min Relay – Maplins P/N JM67
PCB strip board
PCB Fuse holder – Maplins KU29
Potting Box – Maplins FD97
Potting compound
Clipsal 5 way Front Plate – Lets Automate P/N 10580
2 x Clipsal Momentary switches – Lets Automate P/N 10583
1 x Clipsal rocker switch – Lets Automate P/N 10605
2 x Clipsal Neon’s Green/Red – Lets Automate P/N 10588 & 10589

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