HVAC Code Lookup

Rheem Furnace Code 59

Soft lockout

Water sensed in the collector box. The control has detected water backing up in the collector box for at least ten seconds and has stopped gas heating. Repeated occurrences send the furnace into a one-hour lockout showing 59 alternating with 10. Cooling still works.

Manual wording: “WATER SENSED ... The IFC looks for current flow from these pins to determine if water is present in the collector box.”

Documented for: (-)97V, (-)96V condensing furnaces

Likely causes, most common first

  1. A blocked condensate drain or the drain trap has become blocked and cannot allow condensate water to flow properly
  2. Wiring to the sensors has been damaged and exposed wiring is touching the furnace sheet metal
  3. Water sensor has been removed from the collector box with wires still attached and the metal probe is touching the sheet metal portion of the furnace

What you can safely check yourself

  • Check the condensate drain line and trap for a clog, and check that the condensate pump (if you have one) is working and its float is not stuck.
  • Make sure the drain line is not kinked, frozen at an outside wall, or draining into a backed-up floor drain.
  • Power cycle once at the furnace switch after clearing the drain.

When to call a technician

If the drain is clear and code 59 returns, the collector box, sensors or their wiring need a technician.

A Rheem furnace throwing this code repeatedly has a reason — clearing the code without fixing the cause just hides it.

Sources

Other Rheem codes