Drain pump
Common dishwasher and washer water-removal part.
Aprilaire 700 Humidifier — Fault Indicators Quick Reference
The Aprilaire Model 700 is a fan-powered bypass humidifier that does not display numeric error codes — instead, it communicates issues through LED status indicators and operational symptoms. The 700’s digital control (Model 62 or 76 humidistat) may display fault indicators depending on the model year. Understanding what the system isn’t doing leads to the correct diagnosis.
| Symptom / LED State | Meaning | Quick Fix |
|---|---|---|
| No humidification, LED off | No call for heat or humidity | Verify thermostat is calling; check wiring |
| No humidification, LED on | Solenoid valve fault or water supply issue | Check solenoid, water line, saddle valve |
| Water draining but no humidity | Water panel (evaporator pad) clogged | Replace water panel |
| Continuous water flow (won’t shut off) | Solenoid valve stuck open | Replace solenoid valve |
| White mineral buildup on panel | Hard water — normal, requires more frequent replacement | Replace panel; consider water treatment |
| Fan not running | Fan motor fault or no power | Check 24VAC; test fan motor |
| Overflow / water on floor | Distribution tray cracked; drain clogged | Inspect tray; clear drain |
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Most Common Issues
No Humidification — Water Supply
The Aprilaire 700 requires a 1/4” water supply line connected to a saddle valve on a cold water pipe. If no water enters the unit when it calls for humidity, check: (1) the saddle valve is fully open, (2) the water supply line is not kinked or frozen, (3) the solenoid valve orifice is not clogged with mineral deposits. Remove the solenoid inlet screen and clean it under running water.
No Humidification — Solenoid Valve
The 24VAC solenoid valve opens when the control calls for humidification. To test it: with the system calling for humidity, measure 24VAC across the solenoid terminals. If 24VAC is present but no water flows, the solenoid valve is stuck or failed — replace it. Aprilaire solenoid valves (part 4655) are available at HVAC supply houses for $15–25.
Water Panel (Evaporator Pad) Clogged
The water panel is a pleated aluminum mesh pad coated with mineral deposits over time. As scale builds up, airflow through the panel is restricted and humidification capacity drops. Aprilaire recommends replacing the water panel annually (or more often in hard water areas). The Model 700 uses Water Panel 45 (part 10). Do not clean and reinstall old panels — they are not designed to be cleaned and reused effectively.
Continuous Water Flow
If water flows through the unit even when there is no call for humidification, the solenoid valve is stuck in the open position. This is usually caused by mineral deposits jamming the valve seat open. Shut off the water supply to the humidifier and replace the solenoid valve. Running continuously can overflow the drain and damage flooring.
Fan Motor Fault
The Aprilaire 700 has a small fan motor that draws supply air through the water panel. If the fan doesn’t run, the unit won’t humidify even if the solenoid opens and water is present. Check that 120VAC is present at the fan motor terminals when the unit calls for humidity. If power is present but the fan doesn’t spin, replace the fan motor (Aprilaire part 4028).
Annual Maintenance Checklist
- Replace Water Panel 45 each heating season
- Inspect and clean the distribution tray (the water distribution orifice)
- Check the saddle valve for drips
- Inspect the drain hose for mineral buildup
- Verify 24VAC control signal reaches the solenoid during a call for humidity
- Check that the outdoor sensor (if installed with the 76 humidistat) is mounted correctly
When to Call a Pro
If water is entering the ductwork or appearing on the floor, shut off the water supply to the humidifier and call an HVAC technician. Water in the ductwork can cause mold and significant duct damage.