Question about Aprilaire 600 Humidifier

3 Answers

Aprilaire 600 only operates in test mode...

The system is installed in automatic mode and operates in "test mode" but will not operate out of "test mode".

Outside temperature is 35-40 degrees and the resistance of the temp. sensor at the humidistadt measures ~27 k Ohm (corresponds to the suggested impedance for this temp.). The humidifier is installed in the supply plenum and the humidistadt is located about 5 feet (farther form furnace) away from the humidifier.

On a side note, I used the manual mode resistor with similar results.

Posted by on

  • 8 more comments 
  • Dragon man Dec 07, 2007

    Have you got your problem fixed? I am having the same problem, only work at test mode and show E3 code once have it set. if you have the problem fixed, please email me thank you in advance.

  • Anonymous Dec 12, 2007

    I have the same problem. My humidifier works in test mode, but won't work in any other mode.

  • chasjl Dec 29, 2007

    Just completed install. My shows 27K ohms from the temp sensor and 30% HH but will not run the humidifier. Test mode works. I think I'll convert it to manual until I can call Aprilaire on Monday.

  • chasjl Dec 29, 2007

    Well, it dosen't work in manual mode either. Only works in test.

  • 34Scarab Dec 30, 2007

    Same Issue, I have a 600A. I have a continue 24v to R & C,
    and 24v to W/G & Cf when heat is called for from the furnace.
    I have 28.5k ohms of resistance in my outdoor temp sensor (35F).

    If the furnace is on and I go to test mode the
    solenoid turns on and the water is applied to the humidifer. If I
    wait 10-15 sec and return the dial out of test mode to a setting of
    7, the humidifer remains on until the call for heat turns
    off. Turning off part seem to be OK. If I repeat the
    process but this time turn the dial CCW, the humidifer will shutdown
    when the dial get around 4, RH of the return is indicating humidity
    level of 40%. I switched to the manual resistor and the same
    results of than the turn off level is at 6 on the dial instead of 4.

    Summary Humidifer seem to know the correct level RH, and it shuts
    down prooerly when the call for heat has end. But it doesn't know
    when to turn on without going in to manual mode. I guess I'll be
    calling Monday also, unless someone has the magic answer. Thanks

  • snuffysmith Dec 31, 2007

    Same as others. Works fine in test mode, shuts off as soon as it is out of test mode. I now find the outside temperature sensor isn't even outside---I traced the wire and found and found the sensor just sitting up above the vent work hanging free as a bird. Is it possible my inside humidity is high enough that the unit just won't kick on? ---Dick G

  • jeffj Jan 05, 2008

    UPDATE: Aprilaire said the humidistats need recalibration so I sent them back to them a couple of weeks ago. Will let you know how it turns out.

  • Raydean Jan 09, 2008

    Same as Jeff. I get a 30% reading only on the humidistat, regardless where the control is set. The test mode does operate the water solenoid.
    I found that the humidifier control circuit board had heated to a point where these were scorch marks on the board above the wire tearmials from the furnace control board. What the this. 600A

  • Anonymous Dec 07, 2008

    Same problem. The read out indicates 47% and has not changed. The unit never turns on except in the test mode. My furnace guy said that it is working properly because it works in the test mode. I will now ask him to replace it.

  • Anonymous Dec 28, 2008

    My aprilare oly operates in test mode and I just replace the filter. How do I get it to work in normal mode



3 Answers

Thank you, got my problem fixed, after spend $275.00 call the service man to come. it come up to all about wrong wiring.all working and happy:) now.

Posted on Jan 05, 2008

  • Level 1:

    An expert who has achieved level 1.

  • Contributor
  • 1 Answer

Well I fixed my problem. It was my fault. I was using installation instructions that I printed from the web, they were for a model 600. The model 600A has a different control and wiring. The model 600 required only one 24V power supply to the R & C terminals. I ran the furnace accesssory power (110v) to the supplied transformer and then to the R & C as required by the model 600. But on the 600A this must be run to the W/G & Cf pair and a seperate continuously powered 24V must be connected to the R&C pair. I bought another transformer, wired everything using the correct diagram and it works great. BTW the E3 code indicates an open circuit on the temperature sensor. Maybe you clipped the wire while stapling it to the joists. Good luck.

Posted on Dec 29, 2007


Call Aprilaire and tell them, this is happining everywhere

Posted on Dec 12, 2007

1 Suggested Answer

  • 2 Answers

SOURCE: I have freestanding Series 8 dishwasher. Lately during the filling cycle water hammer is occurring. How can this be resolved

Hi there,
Save hours of searching online or wasting money on unnecessary repairs by talking to a 6YA Expert who can help you resolve this issue over the phone in a minute or two.

Best thing about this new service is that you are never placed on hold and get to talk to real repairmen in the US.

Here's a link to this great service

Good luck!

Posted on Jan 02, 2017

Add Your Answer

Uploading: 0%


Complete. Click "Add" to insert your video. Add



Related Questions:

1 Answer

Replaced water panel and the light keeps blinking to change it agai...model 700

Sorry to read about your problem, I hope this helps you out.
did you hit the reset

Digital Humidifier Control (Model 700): (Automatic or Manual mode) Check system operation and reset Change Water Panel indicator by setting the knob to "Test/Reset". With HVAC blower operating and HVAC calling for heat, humidifier will operate for one minute. DO NOT LEAVE IN TEST MODE AS HUMIDIFIER WILL NOT OPERATE.

I tried to help you. Please help me and Rate/Vote on my response. We take the time to answer your question. take the time to rate us.Thanks and good luck

4 Thumbs - Very Helpful
3 Thumbs - Helpful
2 Thumbs - Somewhat Helpful
1 Thumb - Not Helpful

Dec 29, 2010 | Aprilaire 700 Humidifier

1 Answer

Aprilaire 700. It works on fan on mode but not otherwise. It's never on and the humidity reading is always way below the setting. It should turn on automatically to bring the humidity up, right?

It appears your Aprilaire model 700 is wired to only operate when your HVAC fan is operated by your thermostat. Your HVAC installer can wire the humidifier control to operate the humidifier during a heat call, fan call or to turn on the fan when there is a need for humidification. Please contact your HVAC installer to have them change the wiring.

Thank you for giving us the opportunity to be of service

Brad Uselmann
Technical Support
Research Products Corporation

Nov 01, 2010 | Aprilaire 700 Humidifier

1 Answer

How difficult is it to change from manual to automatic mode on my model 700 humidifier?

Based on the information that I have found changing the humidifier from a manual setting to an automatic setting is somewhat easy. It will require you to remove the little blue resistor that is located at the humidistat on the two screws labeled odt and replace that with an outdoor temperature sensor part 8052 that needs to be ran to the outside of the home. Depending on your technical abilities you may be able to perform this procedure, but may need to get a contactor involved.

Feb 09, 2010 | Aprilaire 700 Humidifier

1 Answer

Water only runs with humidistat in test/reset mode. Aprilaire 600 with an Aprilaire 56 Automatic Humidistat, both about 5 years old. Water line is clear, and test mode runs fine for the 1 minute interval....

you need to make sure your humidity level in the house isnt higher then what your humidifier will provide at any givin outdoor temp. this chart is in the owners manual. you cant remove the wires going to the ODS or it will give an error unless you have a resistor to put in its place. Anyway if the humidifier works in test mode according to AA it works so you may have higher humidity than you think, the highest your gonna get is 45% as the temp outside drops it will allow less humidity so it doesnt cause window condinsation (property damage) here is a copy of the chart. the #s on the left are the dial setting
TABLE 2 – % Relative Humidity Guide
Outdoor Temperature (°F)
-10°F 0°F 10°F 20°F 30°F 40°F
10% 10% 10% 15% 20% 25%
2 10% 10% 15% 20% 25% 30%
3 10% 15% 20% 25% 30% 35%
4 15% 20% 25% 30% 35% 40%
5 20% 25% 30% 35% 40% 45%
6 25% 30% 35% 40% 45% 45%
7 30% 35% 40% 45% 45% 45%

Nov 28, 2009 | Aprilaire 600 Humidifier

1 Answer

Chronotherm Three thermostat vs Buderus Logamatic Computer.

The outdoor thermostat senses the the temp of the outside air, and adjust the boiler water temp according to what it knows is best. The reason that the boiler is running longer is the old boiler used to be constantly sending 180ish degree water to the baseboard, now that water may only be 140ish degrees. The idea behind this is to reduce off cycle heat loss, as the greater the temp difference between the air temp and water temp, the quicker you loss heat. The theory in boiler run time is this, the less times it starts and stops, and the long run times will give you the best efficiency. Hope this answers you questions.

Sep 28, 2009 | Honeywell Power Humidifier: Furnace...

1 Answer

Aprilaire 600: water only runs in "Emergency" Heat mode

When your unit is on normal the outside unit works and the inside only the fan runs. your heat pump does not remove any humidity when it operates so the installation cotractor did not wire it to operate then. you can change the wiring on the humidifier to operate all the time by wiring it to the fan (g) terminal then it should work just turn it all the way to the lowest humidity when you are in cooling mode.

Jan 07, 2009 | Aprilaire 600 Humidifier

1 Answer

Error Code E3

I have the same type of Aprilaire humidifier unit with automatic temperature sensing control. My unit also displayed the 'E3' code. The HVAC technician was on site today and replaced the temperature sensing unit that is located outside the house. The humidifier is functioning normally once again.

Dec 03, 2008 | Aprilaire 600 Humidifier

2 Answers

Aprilaire 600 Humidifier


I had this problem several years ago. In order for the water to flow, the outside temperature sending unit must indicate to the controller that it is less than 60F. If not, the unit will not operate outside of test mode. Check the temp outside where your sending unit is (could the sun be heating that side of the house?) and ensure that the circuit to the sending unit is working. I had a bad wire splice inside a wire nut stopping the circuit. Took me a long while to figure it out.

If the outside temp and your sending unit circuit is ok, I wish you luck on your troubleshooting.


Nov 10, 2008 | Aprilaire 600 Humidifier

1 Answer

Not operating-controller questions

are you having problems with your fan blade rotating in the wrong direction? Is yours pushing or pulling water through the water panel? I am very unhappy with my humidity levels in my house.

Nov 02, 2008 | Aprilaire 700 Humidifier

1 Answer

Aprilaire 760 w/ Auto-Trac quit

Have you changed the pad and cleaned it out ?

Feb 02, 2008 | Aprilaire 700 Humidifier

Not finding what you are looking for?
Aprilaire 600 Humidifier Logo

2,594 people viewed this question

Ask a Question

Usually answered in minutes!

Top Aprilaire Humidifiers Experts

Paul Carew

Level 3 Expert

3408 Answers


Level 2 Expert

69 Answers


Level 1 Expert

21 Answers

Are you an Aprilaire Humidifier Expert? Answer questions, earn points and help others

Answer questions

Manuals & User Guides