Rinnai Code 15: Burner Ignition Lockout

Quick Answer

Rinnai Code 15 is a burner ignition lockout that indicates an abnormality was detected specifically during the ignition sequence, not a simple failure-to-ignite like Code 11. The distinction is that Code 15 can occur when the burner lights but the flame quality is immediately abnormal, triggering the combustion monitoring system. Contamination on the burner surface from scale, oil residue, or chemical deposits is the leading cause. Gas pressure outside the acceptable operating range is the second most common trigger. A flame rod that is fouled to the point of providing an intermittent or noisy signal can also cause Code 15. PCB fault is the least common but possible cause.

RinnaiWaterheaterSeverity: highDifficulty: intermediate70% DIY Success

Time to Fix

25–90 min

Difficulty

intermediate

Parts Cost

$12 – $25

Tools Needed

Screwdriver set, Fine steel wool or 400-grit emery cloth

Wrong code?

Not seeing 15 on your display?

Select what your appliance is actually doing and we'll take you to the right guide.

burner ignition lockout

NavienE003

What Does the 15 Code Mean?

Burner locked out after an abnormal ignition sequence, not a simple no-ignition failure. Burner contamination and gas pressure issues are the top causes.

Most Likely Causes

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

Burner surface contaminated with scale deposits, oil residue, or chemical buildup40%

Gas pressure outside the unit's acceptable operating range during ignition24%

Flame rod fouling causing intermittent or unreliable flame signal14%

Venting backpressure disrupting the air-fuel mixture at ignition12%

PCB sending incorrect ignition timing or spark duration10%

Symptoms You May Notice

Code 15 on controller display
Clicking ignition sounds followed by a brief flame and then shutdown
Slight smell of unburned gas near unit immediately after attempted ignition
Unit has produced Code 11 or 12 intermittently before showing Code 15
No hot water despite repeated reset attempts

Can you reset a Rinnai waterheater to clear the 15 code?

After cleaning the burner and flame rod, or after addressing gas pressure, reset by pressing the power button off and on. Allow the fan pre-purge cycle (approximately 30 seconds) to complete before evaluating whether ignition succeeds. If Code 15 returns on the third attempt after repair, call a technician.

Tools Required for Diagnosis

Screwdriver setFine steel wool or 400-grit emery clothSoft-bristle brush (for burner)FlashlightManometer (for gas pressure verification)

Diagnostic Checklist

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

Attempt a single soft reset by pressing the power button off

Attempt a single soft reset by pressing the power button off, waiting 30 seconds, and pressing it back on. Run one hot water demand. Note whether Code 15 returns immediately or after a brief period of operation.

Cut power and gas

Inspect and clean the flame rod

If you have a manometer

Inspect the vent termination for any condition that could cause

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name	OEM Number	Estimated Price
Flame Rod (Flame Sensor)100074985 · $12–$25	100074985	$12 – $25

Verify part fitment for your Rinnai model

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs

Labor Approach

Our Verdict

REPAIR

Estimated Cost: $19 (Parts) vs $1250 (New Machine)

Frequently Asked Questions

What is the difference between Rinnai Code 11, Code 12, and Code 15?

Code 11 means the unit never ignited during 3 attempts; no flame was detected at all. Code 12 means the unit successfully lit but the flame went out during operation. Code 15 means the unit began an ignition sequence but an abnormality was detected at or immediately after ignition, causing a lockout. Code 15 is more specific to the quality of the ignition event, not simply whether ignition occurred or sustained.

How do I clean the burner on a Rinnai water heater?

Turn off gas and power. Remove the burner access panel. Use a soft-bristle brush to gently dislodge deposits from the burner surface and ports. Do not use metal brushes, wire, or compressed air directed into ports, as this can damage the burner material. For oil residue, wipe gently with a cloth moistened with isopropyl alcohol and allow to dry completely before reassembling.

Why would Code 15 appear after a power outage?

After a power outage, the PCB may reset its timing parameters. In some cases the ignition timing or spark duration is slightly off after a hard power reset, especially on older units. This can cause a momentary abnormal ignition event on the first startup after power is restored. A single occurrence of Code 15 immediately after a power outage is often transient and resolves on the next reset and heating attempt.

Is Code 15 the same as a hard lockout?

Code 15 is a safety lockout but it is a resettable lockout, not a hard permanent lockout. You can clear it by pressing the power button. Unlike Code 14 (thermal fuse) which requires a physical repair before the unit will operate again, Code 15 simply requires a reset after addressing the root cause. If Code 15 returns every cycle, treat it as an unresolved fault requiring diagnosis.

Can a gas pressure spike cause Code 15?

Yes. An elevated gas pressure at the exact moment of ignition creates an overly rich mixture at the burner, which can cause an abnormal ignition event that the combustion sensor detects and flags. This is more likely in the morning during low-usage hours when utility supply pressure is highest, or on LP systems when the tank is newly filled and pressure is at maximum. Measuring gas pressure under firing conditions with a manometer can confirm this pattern.

Related Rinnai Waterheater Error Codes

Code: HUBRinnai Tankless Water Heater Error Codes: Complete Guide Code: 11Rinnai Code 11: No Ignition Fix for RU and V Series Tankless Heaters Code: 12Rinnai Code 12: Flame Failure During Operation Code: RESETHow to Reset a Rinnai Tankless Water Heater: All Models Guide

Same Fix on Other Brands

Navien waterheaterE003: Navien E003 Error Code: Ignition Failure Fix for NPE and NCB Series

Models Known to Experience 15 Errors

This repair applies to most Rinnai waterheaters with this error code. Common model numbers include:

RUR98iN, RU199iN, RU98eN, V65iN, RL75iN, RU160iP

Last verified for technical accuracy on March 14, 2026