59 Water sensed / blocked drain

What the control is telling you

Condensate has reached the electronic water level sensor and gas heat is shut down. If it happens again within 5 minutes of the next attempt in the same heat call, the control enters a 1-hour lockout (59 and 10 alternate). On first start-up or after summer the dry trap may cause this up to 4 times while it primes.

Applies to: R95P (R95PA040-115)

Likely causes

• Blocked condensate drain, trap or vent
• Dry trap on first firing (self-priming)
• Condensate line tied into a common drain with an A/C coil located below
• Freezing drain line

Test and repair steps

1. Check the condensate trap, drain line and drain vent for blockage; clear and flush.
2. On a new install or first firing of the season allow the trap to prime (may repeat up to 4 times, more likely on horizontal installs).
3. Make sure the furnace drain is not tied into a common drain with an A/C coil below the furnace.
4. Check heat tape if the drain runs through unheated space.
5. Check the drain vent riser height option chosen (overflow vs. shutoff).
6. Check the water sensor and its wiring if the drain is clear.

Settings for these units

Clearance to combustibles (all models) · R95P

Same values for R95PA040 through 115.

Column order read from a rotated drawing header - confirm on the furnace clearance label.

Models that show this code

6 models in R95P

Other codes on the same units

• 22 Main limit open
• 26 Line and neutral reversed
• 33 Rollout switch (MRLC) open
• 55 Pressure switch stuck closed
• 57 Pressure switch stuck open
• 58 Water sense circuit open
• 61 Blower fault - blower not running
• 93 Internal control fault