Rinnai Tankless Water Heater Error Codes: RU and V Series

Quick Answer

Rinnai tankless water heater error codes indicate specific system faults like ignition failure or venting issues. The most common fix is checking the gas supply and air intake for blockages before performing a power reset.

Rinnai units are finicky about air and gas ratios, so when they throw a code, they mean business. Ignore it and you're looking at a cracked heat exchanger or burned-out gas valve down the road, both of which cost way more than fixing the original problem. Honestly, about 70% of the codes I clear in the field don't require a single new part, just some cleaning and a proper reset.

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About These Rinnai Waterheater Error Codes

OK so here's the deal. Rinnai codes are two-digit numbers and each one points to a specific system, which is actually really useful when you're trying to figure out what's wrong. Gas, venting, ignition, heat exchanger, each one has its own number. I always check the gas shutoff and vent cap first before I even open the cabinet, because that combination solves more than half the service calls I get on these units.

Most Common Error Codes

Dirty or failing flame rod (codes 11, 12, 15)40%

Gas supply off or low pressure (codes 10, 11, 17)24%

Combustion fan failure or blockage (codes 63, 61)14%

Venting restriction or backpressure (codes 55, 12)12%

Scale buildup on heat exchanger (codes 14, 32)10%

Symptoms You May Notice

A two-digit number flashing on your digital controller right after the unit tried and failed to fire up.
You turn on a hot tap and get cold water, or maybe a brief burst of warm and then nothing.
You can hear the igniter clicking away but the burner never actually lights, or it catches for a second and then cuts right back out.
A faint exhaust smell near where the vent pipe exits the building, especially on windy days when there's some backflow happening.
The unit makes its normal startup sounds but shuts off completely within about 5-10 seconds of trying to fire.

Tools Required for Diagnosis

Phillips #2 screwdriverFlat-head screwdriver (for terminal blocks and panel clips)Flashlight or headlamp (for vent inspection inside and out)Digital multimeter (Fluke 117 or equivalent)Manometer or U-tube gauge (for gas pressure testing)Fine Scotch-Brite pad (for flame rod cleaning)Adjustable wrenchDescaling pump kit or submersible pump with bucket (for heat exchanger flush)

How to Identify Your Error Code

Frequently Asked Questions

How do I read the error code on my Rinnai water heater?

The code shows as a two-digit number right on your digital controller display. If you've got multiple units linked together, the controller usually specifies which unit is throwing the fault. Missed it before you reset? Hold the Priority button for about five seconds to get into maintenance mode, then scroll through the last nine stored faults. Write down exactly what you see, because that number is the difference between a $15 flame rod cleaning and a $400 service call to diagnose something you could've told me over the phone.

Can I reset a Rinnai error code without fixing the problem first?

You can try, but you're almost certainly wasting your time. Rinnai units are built to protect themselves from damage, so if they see a real fault, they'll keep shutting down until you fix the actual cause. I've been doing this 15 years and I've seen maybe a handful of cases where a simple reset cleared a genuine problem long-term. Usually it just buys you 20 minutes before the code is back. Fix the root cause first, then reset.

What are the most common Rinnai error codes?

Code 11 is by far the most common thing I see on service calls. It means ignition failure, and nine times out of ten it's a flame rod with carbon buildup that just needs a quick scrub with a fine Scotch-Brite pad. No parts, no tools really, five minutes. Code 10 is next, usually gas supply or a blocked exhaust. Code 14 is the thermal fuse tripping because the unit overheated from scale buildup on the heat exchanger. Code 25 is a condensate sensor issue and that's specific to the RU condensing series.

Do all Rinnai RU and V series models use the same error codes?

Mostly yes. Rinnai keeps their diagnostic language pretty consistent across the lineup, which is genuinely nice when you're trying to troubleshoot. The main difference is the RU condensing series has extra sensors for the condensate trap, so you'll see codes like 25 that a V series owner will never deal with. The V series is non-condensing, so its code list is a bit shorter. But the core codes like 10, 11, 12, 14, 31, and 32 work the same way across both lines.

When should I call a technician for a Rinnai error code?

If you've confirmed the gas is on, the vent's clear, and you've done both a soft and hard reset and the code keeps coming back, call someone. Anything involving the gas valve itself, the main PCB, or descaling the heat exchanger with a pump system requires tools most homeowners don't have. Gas valve alone is usually $180-300 in parts. The PCB can run $250-400. And if you smell anything burning or see scorched components inside the cabinet, don't even try to reset it. Shut it down and call a tech.

How do I know if my heat exchanger needs descaling?

Code 14 is your first clue, but there's another easy tell. If your tankless unit used to handle two showers running at once but now struggles with one, scale is probably choking the heat exchanger passages. A descaling kit runs about $40-60 and pumps white vinegar or a commercial descaler through for a couple hours. I replaced three heat exchangers last month that honestly could've been saved with regular maintenance. If you're on hard well water, descale every two years. City water, you can usually stretch it to three or four.

Related Rinnai Waterheater Error Codes

Code: 11Rinnai Code 11: No Ignition Fix for RU and V Series Tankless Heaters Code: 12Rinnai Code 12: Flame Failure During Operation Code: 10Rinnai Code 10: No Gas Supply or Gas Valve Failure Code: 63Rinnai Code 63: Combustion Fan Error Code: 17Rinnai Code 17: Gas Valve Abnormality Code: 61Rinnai Code 61: Combustion Fan Motor Failure Code: 14Rinnai Code 14: Thermal Fuse Blown on Heat Exchanger Code: 55Rinnai Code 55: Combustion Abnormality Detected Code: NO-HOT-WATERRinnai Tankless Water Heater No Hot Water: 6 Causes and Fixes Code: 79Rinnai Code 79: Combustion Air Temperature Sensor Fault Code: 15Rinnai Code 15: Burner Ignition Lockout Code: RESETHow to Reset a Rinnai Tankless Water Heater: All Models Guide Code: 52Rinnai Code 52: Modulating Gas Valve Error Code: 25Rinnai Code 25: Bath Fill Error (ThermaCirc Models)Code: 32Rinnai Code 32: Outlet Water Temperature Too High

Same Fix on Other Brands

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Models Known to Experience HUB Errors

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

RUR98iN, RU199iN, RU98eN, V65iN, RL75iN, RU160iP, V94iN, RU180iN, V75iP, RU199eN

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 14, 2026