Central Heating Automation – Review

Submission by Dean Smith – After moving into Orchard House, we soon realised how much you take little things for granted. In our previous house the Central Heating Controller had been in the kitchen and both my Wife and I frequently made use of the “+1 Hr” buttons for both Heating and Hot Water.

In Orchard House however, the controller was upstairs inside the airing cupboard. Now it’s not a big house, but that was still more of a walk than I thought was strictly necessary 😉 I considered relocating the Controller, but there were no easy cable runs for the Mains cables required. Having recently installed a Comfort alarm, I’d been considering what I could use the Digital Outputs for. Slowly I managed to put 2 and 2 together and get close to 4. I’d install some relays that could control the Heating (240V) on the Comfort Outputs (12V). A 12V cable from Comfort into the airing cupboard was much easier.

Working out how to wire the relays into the Heating first required me to understand the Heating Circuit itself. The documents I had showed me I had a “Standard Honeywell Y-Plan” system which uses a 3-way valve. After equal measures of Googling and head scratching I finally persuaded myself I understood how the circuit for the 3 way valve worked. Something that was a good deal harder than I expected. I’m sure there are good reasons for why it was designed like that – but I had to make do with just working out the how. There is some good info on the Honeywell site itself. A 3-way setup requires feeds from both a “HW ON” and a “HW OFF” signal which complicates things slightly as I wanted to ensure I could use the current controller for normal timings, but override it when required.

The circuit I came up with uses 2 relays. 1 for the Heating and 1 for the Water. The Water is a Dual Contact change-over. This allows both the “HW ON” and “HW OFF” signals from the current controller to be disconnected and replaced with the “HW ON” signal regardless of their previous states. The Heating relay is in fact the same – but uses only a single contact. Power is taken from the existing feed on the controller so everything can still be isolated exactly as before.

Relays Mounted I mounted the two relays on a small section of DIN rail screwed into a standard surface mount wall box. The height of the relays meant I had to cut 2 holes in the face plate. Not ideal, but at least I can see the indicators on the relays themselves. I wired up the relays, sticking closely to the standard used for the original controller. There are in fact 3 mains cables required. 2-Core supply (actually the Neutral isn’t required but was added for completeness). 3-Core from the controller. 3-Core back to the wiring junction box. There’s also the 12v cable from the alarm, which powers the relays. Fortunately the controller had some spare terminals so in fact I didn’t have to disturb any wiring in the main Wiring Box and could easily take the relays out of the system and revert to the original wiring if I ever need to.

The relay mounting box was installed next to the other heating controls in the airing cupboard. I’m not happy with the entire install but a complete re-wire of the Heating will have to wait.

Comfort uses an output for each relay. Each output is triggered for an hour (using Comforts own timers). I can generate the trigger via X10 (IR, from HomeSeer or mini-controller), via a Comfort KeyPad (rarely used) or via the phone. Despite initial Wifely scepticism she seems to manage to show most people that she can turn the heating on from the Pronto remote in the lounge….

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