Symptoms
- Puddle or drip near the base of the furnace
- Water stains on the floor around the unit
- May appear only while the furnace is actively running
Likely causes
- CommonClogged or disconnected condensate drain lineA blockage backs water up until it overflows somewhere in the system.
- CommonCracked condensate drain trap or tubingPlastic fittings can crack with age, especially where they connect to the furnace.
- PossibleFailed condensate pumpIf the pump can't keep up or has failed, water backs up and overflows.
- PossibleHumidifier attached to the furnace leaking separatelyA whole-house humidifier's water line or drain can be the real source, not the furnace itself.
- Less commonImproperly sloped or damaged ductwork causing condensation drip (non-condensing furnaces)In older furnace types, flue condensation can occasionally drip if the vent pipe is pitched wrong.
What to do
- Turn the furnace off to stop the leak from getting worse while you investigate.
- Trace the water back to its source; follow the condensate line from the furnace to where it drains.
- Check all tubing and fittings for visible cracks or loose connections.
- If there's a humidifier attached, check its water supply line and drain separately.
- Clear any visible clog in the drain line as described for a clogged condensate line.
- Mop up standing water and place a towel or pan under the unit until the cause is fixed to prevent floor damage.
- If you can't find or fix the source, leave the furnace off and call a technician rather than risk water damage or electrical issues.
Tools and parts
- Towels
- Bucket
When to call a pro
Call an HVAC technician if you can't locate the leak source, if it involves a cracked internal component, or if water has reached electrical parts.
Safety
Use caution
Keep water away from electrical connections and the control board; if water has reached electrical components, leave the furnace off and call a technician.