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Rinnai Tankless Water Heater No Hot Water: Error Code, Flow, and Flame Fixes

Quick Answer

Rinnai tankless not producing hot water: check the error code on the controller. Code 11 = no ignition (check gas supply valve is open, gas pressure at least 4 inches water column). Code 25 = scale surging in the heat exchanger (annual descaling with vinegar solution required). Code 10 = blocked air intake or exhaust - check for bird nests or debris.

Rinnai tankless water heaters display error codes on the front panel when hot water is not produced. The most common Rinnai no-hot-water codes: Error 11 = no ignition (dirty flame rod, gas supply issue, or igniter failure). Error 12 = flame loss during operation (gas pressure fluctuating or venting issue). Error 14 = thermal fuse activated (overheating from scale buildup). LC = scale buildup in heat exchanger (descale with vinegar). The #1 DIY fix for Rinnai Error 11: clean the flame rod with fine sandpaper or steel wool. The flame rod detects the pilot flame through electrical conductivity - oxidation on the rod prevents detection, and the unit thinks the flame went out. After cleaning, reset by pressing the ON/OFF button twice. If Error 11 persists, check that the gas supply valve is fully open and the gas line is not kinked.

RinnaiWaterheaterSeverity: mediumDifficulty: intermediate75% DIY Success

Time to Fix

15–90 min

Difficulty

intermediate

Parts Cost

—

Tools Needed

Multimeter, Screwdriver

What Does the NO-HOT-WATER Code Mean?

Rinnai no hot water: Error 11 = clean flame rod with sandpaper (#1 fix).

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Code 11 - ignition failure35%

Code 12 - flame loss mid-operation25%

Code 25 - heat exchanger scale buildup20%

Code 10 - air/exhaust blockage15%

Flow sensor fault5%

Symptoms You May Notice

Appliance exhibits no hot water behavior

Can you reset a Rinnai waterheater to clear the NO-HOT-WATER code?

Unplug 60 seconds. Plug in and test.

Tools Required for Diagnosis

MultimeterScrewdriverFlashlight

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

Follow the brand-specific diagnosis in the guide above.

Check for error codes on display or LED patterns.

Run manufacturer diagnostic mode if available.

Frequently Asked Questions

How much does Rinnai waterheater repair cost?

Most repairs $100-400 depending on the component.

Worth repairing or replacing?

If under 18 years and repair under 50% of replacement cost, repair.

DIY or professional?

Many fixes are DIY. Gas and sealed systems need professionals.

Last verified for technical accuracy on March 14, 2026