Rinnai Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater 25 Error Fix: Condensate Drain Blockage

Error code 25 on the Rinnai Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater means: Condensate Drain Blockage. The condensate drain system is blocked or restricted. This code applies to condensing models only (RU series, RUR series, RX series, and RSC combo boilers). Condensing tankless water heaters extract additional heat from exhaust gases, causing water vapor in the exhaust to condense into liquid. This acidic condensate (pH 3-4) must drain properly through the condensate trap, neutralizer (if installed), and drain line. Error 25 indicates the condensate level switch or sensor has detected backed-up condensate. Common causes: (1) Clogged condensate neutralizer — the calcium carbonate media in the neutralizer dissolves over time and can clog. Replace the media or the entire neutralizer cartridge. (2) Blocked drain line — sediment, algae growth, or ice (in cold installations) can block the condensate drain tubing. Flush the drain line with warm water. (3) Frozen condensate line — if the drain line runs through an unheated space, condensate can freeze and block the line in winter. Insulate the drain line or reroute to a heated area. (4) Failed condensate sensor. Non-condensing models (V, RL, RE series) should not display this code.

The most successful fix is "Replace the Condensate Neutralizer Cartridge" (medium difficulty, ~30 minutes). Estimated DIY cost: $15-$25. HomeMD has 2 community-ranked fixes for this error.

This error is rated warning severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Replace the Condensate Neutralizer Cartridge") is rated medium difficulty and takes about 30 minutes. Tools needed: Adjustable pliers, Bucket, Gloves.

DIY cost: $15-$25. Professional repair typically costs $120-$180. Many homeowners save money by trying the top-ranked community fix first.

The Rinnai Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater has 8 other known error codes, including: 02 (Ignition Failure), 03 (Bath Fill Function Abnormality), 05 (Blocked Exhaust / Air Supply), 10 (Blocked Exhaust — Air Pressure Switch), 11 (No Ignition), and 3 more.

Error code 25 also appears on 8 other Rinnai models: Rinnai RE180iN RE Series Non-Condensing Tankless Water Heater, Rinnai RL75iN RL Series Tankless Water Heater, Rinnai RL94iN RL Series Tankless Water Heater, Rinnai RSC160iN Condensing Combi Boiler, Rinnai RU130iN Sensei Super High Efficiency Plus Tankless Water Heater, Rinnai RUR199iN Sensei Recirculating Tankless Water Heater, and 2 more. The fix may vary by model, so check each model's specific page for tailored repair steps.