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Rheem 59: Water sensed in the collector box; gas heat will not run

Ref. RHEEM-59 · From the Rheem furnace manual · Updated 2026-10-23

Status code59Rheem
What it means

Water sensed in the collector box; gas heat will not run.

Basic checks firstfurnace
How it shows: Dual 7-segment display: 59

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§1Likely causes

  • Blocked condensate drain or drain trap
  • Damaged sensor wiring touching sheet metal
  • Water sensor removed and probe touching sheet metal

§2Safe DIY steps

  1. Turn off power, then check the condensate drain line and trap for blockage
  2. Technicianrepair sensor wiring or reinstall sensor
Safety firstIf you smell gas, do not touch any electrical switch or use a phone in the building; leave immediately and call your gas supplier from outside. Turn off electrical power at the furnace switch or breaker before opening any panel, and never bypass or jumper a limit, rollout or pressure switch. Gas valve, burner, venting, wiring and control-board work should be done by a licensed HVAC technician.

§3When to call a pro

Call a licensed HVAC technician: if clearing the drain does not fix it.

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§4Other Rheem codes

10Rheem

One-hour lockout, caused by repeated failed ignition (11), water sensed (59), dead blower (61), internal fault (93), flame lost 5 times (13) or unexpected flame (14).

11Rheem

Failed ignition. After four failed attempts the control enters one-hour lockout (10).

12Rheem

Low flame sense: flame sense current is weak or marginal. Furnace keeps running.

13Rheem

Flame lost after established.

14Rheem

Flame present with gas valve off. Extremely critical; furnace will not operate.

30Rheem

Open fuse, usually from a 24 VAC short to common or ground.