25 Moderate Moderate DIY

Rinnai Tankless Water Heater 25 — Condensate Drain Blocked (Condensing Models)

Rinnai Tankless Water Heater · Error code 25

What 25 Means

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

Symptoms

  • Code 25 on condensing model (RU, RUR)
  • Water dripping from cabinet
  • Reduced or no hot water

Common Causes

1
Condensate trap clogged

Sediment or biofilm in trap or float.

2
Frozen condensate line

Outdoor or unheated section froze.

3
Improperly sloped drain

Negative slope creating water trap.

4
Sagging or kinked drain hose

Restricts flow.

5
Failed condensate level switch

Float sensor stuck.

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.

Parts You May Need

If diagnosis points to a failed part, these are the common replacements. As an Amazon Associate we earn from qualifying purchases.

Common replacement Condensate trap assembly View on Amazon→ Common replacement Condensate neutralizer cartridge View on Amazon→

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 →

Verified against manufacturer documentation: rinnai.us

Always unplug an appliance before servicing it. This guide is for informational purposes and is not a substitute for a qualified technician.