Rinnai · Tankless Water Heater Moderate

25 — Condensate Drain Blocked (Condensing Models)

Condensate is not draining from the secondary heat exchanger. The condensate trap or line is blocked or frozen.

Keep using it?
Yes, with caution
DIY difficulty
Moderate
Typical cost
$25-45
Verified against
rinnai.us ↗

The fix

Rinnai condensate trap replacement (104000255 / 107000267, model-specific)

Condensate not draining — trap or line blocked or frozen

$25-45 moderate difficulty 30-45 min Tools: screwdriver, bucket

Diagnose first: This is drain-line plumbing, not the gas/combustion side — safe to clear yourself. First just check the external condensate line and trap for a clog or ice; only replace the trap itself if clearing it doesn't fix the fault. If the line runs outside and freezes every winter, insulating or rerouting it prevents repeat trips.

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Didn't resolve it? Next suspect: Rinnai condensate neutralizer kit (804000074) ($40-60)

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How to fix it

  1. Power off the unit.
  2. Disconnect and clean the condensate trap — flush with warm water.
  3. Inspect the drain line for sags, kinks, or freezing.
  4. Re-route drain with continuous downward slope and insulate any exterior runs.
  5. Re-test by running unit and watching drain output.
  6. If trap and line are clear, replace the condensate level switch.

Why it happens

Typical signs: Code 25 on condensing model (RU, RUR) · Water dripping from cabinet · Reduced or no hot water

  • Condensate trap clogged Sediment or biofilm in trap or float.
  • Frozen condensate line Outdoor or unheated section froze.
  • Improperly sloped drain Negative slope creating water trap.
  • Sagging or kinked drain hose Restricts flow.
  • Failed condensate level switch Float sensor stuck.

More Rinnai tankless water heater codes

02 02 — Power Interruption / Memory Loss 03 03 — Loss of Communication / EZConnect Issue 10 10 — Air Supply or Exhaust Blockage 11 11 — No Ignition 12 12 — Flame Failure 14 14 — Thermal Fuse / Overheat Cutoff

All Rinnai codes → All tankless water heater codes →

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician. Verified against manufacturer documentation: rinnai.us.