After having a new furnace and AC installed in the summer of 2018, replacing my 20-year old equipment, the existing AprilAire 600 whole-house humidifier behaves differently than before.

During the time that the furnace burners are not firing, the humidifier panel is lit, the water runs when it needs to, and the humidity is adequate in moderate weather.  When the burners kick on, the humidifier control panel powers off completely and nothing happens until the burners kick off again. Once the burners turn off, the panel powers up, displays an error message (r1) for a few seconds, and resumes operation.  This is really only a problem when the weather is really cold because not enough water gets to the panel when the furnace fires more frequently. The furnace is Trane, 2-stage and the AC is American Standard, 1-stage. The AprilAire controller is digital, and the thermostat is Ecobee.   Is there a common or likely mistake during install that could cause these symptoms?

Furnace model: S9V2B080U3PSBA AC model: 4A7A6030J1000A

Furnace Terminals

Humidifier Controller Terminals

Ecobee Terminals

Wiring description

  • What model is the new furnace, and can you post photos of the wiring at the furnace? Oct 8, 2019 at 3:18
  • Furnace: S9V2B080U3PSBA AC: 4A7A6030J1000A Oct 8, 2019 at 3:41
  • I have added pictures, in order: Furnace terminals, Humidifier Controller terminals, Ecobee Thermostat terminals, an attempt to describe the wiring of everything. Oct 8, 2019 at 4:02
  • @ThreePhaseEel, in your opinion, is this "power off when burners fire" behavior normal? Oct 16, 2019 at 19:52
  • I seriously doubt it is normal... Oct 16, 2019 at 23:08

1 Answer 1


Humidifier must run while the furnace runs

Aprilaire model 600 operates on the principle of evaporation. It's an evaporative cooler ("swamp cooler") installed in the heating system. It's installed as a bypass between the furnace outlet and the cold air return; a portion of the hot air coming out of the furnaces goes through the Aprilaire 600, picks up moisture, and goes immediately into the furnace air return.

Because of its operation, it's very important that the water valve can operate while the furnace blower and burners are running. Otherwise, each heating cycle of the furnace can add no more water than whatever is left standing in the humidifier's pad.

ecobee could control the humidifier

The ecobee3 and ecobee4 thermostats can control that Aprilaire 600 directly. Is yours one of these? Do you prefer to use the Aprilaire controller instead, or is this arrangement simply a result of not knowing the Ecobee has this capability? It's not impossible to make everything work correctly with the Aprilaire controller but it's simpler to let the ecobee manage humidity for you.

Wiring for ecobee control of humidifier

When the ecobee is installed there's a setup wizard that figures out whether and how you have a humidifier connected. After getting the wiring sorted out we'll circle back to fixing that configuration (I'll edit it in after you confirm this is the direction you want to go).

If your ecobee model is one that supports accessories there's an easy way and a less-easy way to wire it. The easy way involves the transformer that came with the Aprilaire unit. Make a ring: one transformer wire connects to one water valve wire, the other water valve wire connects to one of the ecobee ACC terminals, the other ecobee ACC terminal connects back to the second transformer wire.

The less-easy way powers the Aprilaire 600 water valve using the transformer that's already in the furnace. This is how I have mine set up, but I don't recall exactly which wires I used. I'll have to edit to add detail on that..

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