Aprilaire 600 problem

the float may be bad or sticking allowing water to run continusly even when unit is off.

Doesn't the float valve on the water sump control the level of water in the sump?

Do you have water to the valve? (Like loose the nut on the tubing-- does water come squirting out?)

If not, you can't get humidity into your system, without water in that sump or pan!
The mat can be turning-- but if it is not SOAKING WET!-- you get no humidity in the house!.

Could the main shut off valve be plugged?--

Bottom line is-- the Humidifier needs a steady supply of water-- It will go thru gallons of water every day, this time of the year!

Mack B

Apply power directly to the solenoid valve from the transformer and check if the solenoid opens and lets water in, If not then the solenoid is bad. If the solenoid does open up by applying power directly from transfomer then check the wiring make sure it's all tight and that the currentsensing relay/sail switch is good. Also i would check to make sure there is a strainer on the inlet of the solenoid valve and that it is clean, sometimes sediment builds up on the inside of the solenoid and can shorten the life of it.

if your using an outdoor thermostat then it may not be connected properly or the manual mode resistor wires are touching. these are connected on the humidistat just to the right of the H H terminals

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
1 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%

Yes, just check to see if you have 24 volts going into the solenoid. If you do and it is not opening its probably bad. Since you verified the water lines, filter, orifice and saddle valves are not obstructed. Change the solenoid valve. When you price the part. (it's not cheap) consider paying about 30% more and just change the whole unit.
Good luk
HVAC Teacher

the change water panel light is just a timer. it does not sense that the water panel actually needs to be replaced. sounds like you have a solenoid issue. if you have water to the solenoid and are certain you are getting 24v to it, the solenoid is ethier bad or plugged with calcium. most likely calcium. sometimes you can take them apart and clean them. so, it you can hear clicking at the solenoid when you turn the humidstat up and down. try cleaning it.

http://www.aprilaire.com/themes/aa/en/manuals/600a.pdf Read page thirteen and there is a inlet water filter that may be cloggeed. Let me know if you need anything else.

solenoid valves dont just burn up just like that you have a recurring restriction due to bad water.Check the saddle valve at the water heater first then check for postive water flow at inlet to the solenoid valve,if you have water flow the valve is clogged with sediment.

Your solenoid may have seized. The best way to check is remove the cover off the humidifier pad housing, remove the rubber tube of the distribution tray and see if water comes out while in the test mode. If you have a volt meter you can test to see if you have 24volts at the two wires connected to the solenoid. If you have 24volts there but no water ,the solenoid is bad if not you may have a bad humidistat or humidifier transformer depending on how it is wired.