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.

In my experience, Code 15 usually points to a 'dirty' ignition where the burner actually lights but the flame looks wrong to the sensors. I often find this on units installed near laundry rooms or kitchens where lint and grease coat the burner plate. It is a more sensitive fault than a standard ignition failure, often requiring a deep cleaning of the burner manifold rather than just swapping out parts.

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

What Does the 15 Code Mean?

Think of Code 15 as the Rinnai way of saying the combustion quality is unsafe. While a Code 11 is a total failure to spark, this code means it fired up but the mix was off. Nine times out of ten, we are looking at gas manifold pressure issues or a burner surface covered in white scale flakes that fell from the heat exchanger.

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?

You can clear the lockout by tapping the power button on the controller off and then back on. However, if the unit fails to stay lit after two resets, stop and check the burner. Repeatedly forcing a reset with an abnormal flame can lead to soot buildup inside the heat exchanger, which turns a simple cleaning into a very expensive repair.

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.

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

Frequently Asked Questions

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

Code 11 is a 'no-show' where the unit never saw a flame at all. Code 12 is a 'dropout' where it was running fine but the flame vanished. Code 15 is the 'picky' code. It means the unit successfully lit, but the flame signal was messy, unstable, or didn't meet the safety parameters programmed into the board. It is a warning that combustion is happening, but it is not happening correctly.

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

To clean the burner, you need to be careful. After shutting off the gas, I use a soft nylon brush to sweep away any debris like scale or dust. Never use a wire brush or high pressure compressed air, as you can easily deform the burner ports or blow junk further into the gas manifold. If there is greasy buildup from being near a kitchen, a little rubbing alcohol on a lint free cloth works wonders to restore the surface.

Why would Code 15 appear after a power outage?

When the power comes back on, the PCB runs a self-diagnostic. If the unit was in the middle of a heating cycle when the power cut, there might be residual heat or unburned vapors in the chamber. That first attempt to relight can be a bit 'rough' as the fan recalibrates its speed. Usually, one or two manual resets will clear this 'ghost' code and the unit will return to normal operation.

Is Code 15 the same as a hard lockout?

No, it is a soft lockout. A hard lockout, like a blown thermal fuse, requires you to replace a part before the unit will ever turn on again. Code 15 can be reset from the controller. That said, if you find yourself resetting it every morning, you are ignoring a growing problem. Most likely, your burner is getting dirty or your gas regulator is starting to fail, and eventually, the unit will stop resetting entirely.

Can a gas pressure spike cause Code 15?

Gas pressure spikes are a classic trigger for Code 15. If your house regulator is sticking or if you are on a propane system with a new tank, the initial burst of gas can be too much for the Rinnai to handle at the moment of ignition. This creates a rich, unstable flame. I always use a manometer to watch the pressure the second that gas valve clicks open to ensure it stays within the range listed on the rating plate.

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

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 14, 2026