Wireless Boiler Zone Controller

Code: https://github.com/ryanrdetzel/Zone-Controller

My house is old enough that when they ran the thermostat wiring it only had two wires which means using modern “smart” thermostats is not an option with out some often ugly creative solutions. My ideal thermostat setup would allow me to control all of my heating and cooling via my home automation setup but with no way to control the boiler this is not currently an option. This project tries to solve that problem by allowing me to control each boiler zone via mqtt message. To accomplish this my plan is to build a zone controller that sits near the boiler and triggers the 24v relays to turn zones on or off. The controller will connect to wifi and accept mqtt messages to trigger each zone. The controller itself will be dumb, basically accepting simple commands and that's it. It will not schedule or alert at this time.

Because this controller is considering dumb it will rely on another system to tell it when to turn on and off. Most likely I will use my Home Automation setup for this. I will also need to add some additional temperature sensors around the house to report the correct temperature in each zone.

Version 1

  • Wireless (probably wifi but could use RF or BLE to)
  • Accepts basic on/off commands for each of the four zones via mqtt. boiler/zone1/on
  • Powered via wall powered ac adapter, probably 5v
  • Physical buttons on the controller that allows it to be powered on/off and override control. Override control will allow me to manually trigger the heat on/off if something is broken or for testing/maintenance.
  • LEDs for each zone that show the current state of the zone. Disable, Enabled, Running

Future Features

  • Audible alerts if something is wrong
  • MCP23017 - I/O Expander
  • Relay board to trigger the existing 24v AC relays.
  • Various buttons to provide physical control of the controller
  • LEDs to provide visual feedback
  • 5v AC power adapater


Here is what the existing zone controllers look like. These take the line voltage (120v AC) and transform it down to 24V AC which is what the relays use to trigger the pumps. My plan is to hook an additional wire to the low voltage 24VAC and use my own relays to trigger these on the way way the thermostat does.

Basic circuit prototype on a breadboard. You can see it using a WeMos D1 mini, a IO Expander and a test LED.