Rinnai Heat Exchanger Leak in Glendale, AZ: A New Part, Not a New Water Heater

By Pridemark Plumbing · Licensed Arizona Contractor, ROC #319398

A Rinnai heat exchanger leak often shows up like this. You turn on the shower and the water never gets hot. Then you walk out to the tankless heater on the outside wall and find water where it shouldn’t be, heading for the wiring.

That’s how a call started for us in May 2026. A homeowner in the Marbella Ranch neighborhood of Glendale, Arizona 85307 had no hot water, and water was leaking from their outdoor Rinnai tankless toward its electrical parts. They’d lived in the home about two and a half years, they were new to Pridemark Plumbing, and they didn’t know whether the heater was still under warranty.

Why Is My Rinnai Tankless Water Heater Leaking Inside the Cabinet?

Water inside the cabinet, instead of at the pipes underneath, can mean a Rinnai heat exchanger leak. Every gallon of your hot water runs through the heat exchanger’s copper tubes while a gas burner fires below them.

The heat exchanger heats and cools every time a tap opens and closes, and hard water leaves scale, a mineral crust, inside its tubes. When a heat exchanger lets go, the water drips down through the cabinet toward the controls.

Is It a Rinnai Heat Exchanger Leak or Just a Loose Fitting?

Where the water starts tells you. Drips at the connections under the heater usually mean a fitting or valve, often a simpler repair, while water inside the cabinet can mean the heat exchanger. Water from the pressure relief valve’s line means that safety valve is letting water out.

A cracked heat exchanger is on Rinnai’s own troubleshooting chart, which tells technicians to “Check heat exchanger for cracks or separations.” Here, Donnie, our plumber on this job, took the front cover off and traced the water to the heat exchanger itself, so tightening a fitting wasn’t going to fix it. We didn’t record what the inside of the old one looked like, so we can’t tell you exactly why it failed.

Is a Leaking Tankless Water Heater Dangerous?

It can be, because a tankless puts water, gas and electricity in one small box. Rinnai’s manual says not to use the heater if any part has been under water, and to have a licensed professional inspect it right away.

On outdoor units, we pay close attention to where the water went, because the control board sits low in the cabinet.

What should you do first if your tankless water heater is leaking?

Shut off the water, power and gas, and leave the cover on:

1. Turn off the water at the isolation valve right below the heater, the shutoff on the cold line coming in.
2. Turn off the power at the circuit breaker or the heater’s outdoor disconnect switch, as long as you can reach it without touching anything wet.
3. Turn off the gas at the manual gas valve, usually right below the heater.
4. Leave the cover on, and don’t keep resetting the heater to see if it comes back.
5. If you smell gas, leave the area right away. From a safe place, call 911 and Southwest Gas, as Southwest Gas tells its customers.

Does Rinnai’s Warranty Cover a Leaking Heat Exchanger?

It can, and on Pridemark Plumbing’s May 2026 job it did. Rinnai’s warranty covered the parts: the heat exchanger, the burner plate and the gas manifold. Once Donnie found the leak, we opened a warranty case with Rinnai before any repair work, because that answer changes what you pay.

If you bought your home with the tankless already on the wall, this part’s for you. Rinnai’s warranty for its Value Series heaters, which include the V65e, says its coverage “extends to the original purchaser and subsequent owners, but only while the product remains at the site of the original installation.” So the warranty stays with the house.

For a home, Rinnai’s Value Series warranty lists 10 years on the heat exchanger, or 12 if the heater went in with a tankless isolation valve kit, the shutoff and flush valves under the heater. Other parts get 5 years and reasonable labor gets 1, all from the date of purchase, with shorter terms for some recirculation setups. Check yours with the serial number on the rating plate.

Can a Leaking Heat Exchanger Be Replaced, or Do You Need a New Water Heater?

Often it can be replaced, and while the heater’s under warranty, Rinnai makes that call. Out of warranty, the call’s yours. Its warranty says Rinnai “will repair or replace the covered product or any part or component that is defective in materials or workmanship,” and that replacing the whole product “may only be authorized by Rinnai at its sole discretion.”

Three Rinnai heat exchanger jobs we’ve done in 2026 show how that plays out:

• This job, May 2026: a new heat exchanger, burner plate and gas manifold under Rinnai’s warranty, in the same heater.
• Buckeye: a new heat exchanger and fan unit on a Rinnai V65i, with warrantied parts.
• Goodyear, September 2026: a two-year-old RE160e leaking from the bottom, where Rinnai authorized a whole new heater.

Same part, different answers. We’ve also done a whole-unit Rinnai warranty replacement in the same ZIP code. Your heater’s age, model and warranty decide which way it goes, so we get Rinnai’s answer before the repair starts.

What Does a Rinnai Heat Exchanger Repair Involve?

On this heater, the repair took eight steps, from the call to a final inspection:

1. Came out the next day after the call.
2. Traced the leak to the heat exchanger with the front cover off.
3. Opened a warranty case with Rinnai, since the homeowner didn’t know the heater’s warranty status.
4. Walked the homeowner through the repair and told them what they’d pay before we started.
5. Replaced the heat exchanger, along with the burner plate and the gas manifold, the part that feeds gas to the burners.
6. Cleaned the unit.
7. Set the burner gas pressure for low fire and high fire with a manometer, then ran a gas pressure test and a leak test.
8. Inspected the whole install against Rinnai’s installation requirements.

The homeowner had hot water again from the same heater on May 5, the day of the repair. Tankless water heater repair like this is part of our tankless water heater service.

Does the gas pressure need setting after a Rinnai heat exchanger repair?

When the gas manifold is replaced, yes. Rinnai presets the burner gas pressure at the factory and says that under normal circumstances it doesn’t need adjusting during installation. A new gas manifold is a different story, and Rinnai’s troubleshooting chart includes “Ensure high fire and low fire manifold pressure is correct.”

Donnie set the low flame and the high flame with a manometer, a gauge for very low gas pressures, and wrote the settings inside the cover for the next technician who opens your heater. The right numbers depend on the model, the gas type and the altitude, so your heater’s rating plate is the source of truth, not a number from another job. Adjusting gas pressure is a technician’s job, never a homeowner’s.

How Do You Keep a Tankless Heat Exchanger From Scaling Up?

Flush it at least once a year and treat hard water. Those were our two recommendations for this homeowner in Marbella Ranch, and Rinnai’s own paperwork backs both. Across the West Valley, most of the leaking tankless heaters we open have never been flushed.

Water in this part of the West Valley often runs harder than Rinnai allows. Rinnai’s manual sets a maximum total hardness of 200 mg/L, milligrams per liter, for this heater. That’s about 11.7 grains per gallon.

Marbella Ranch homes generally get their water from Liberty Utilities, a private water company, rather than the city. Liberty’s 2025 figures for its Litchfield Park system show 150 to 360 ppm, parts per million, the same as mg/L for water, with a highest average of 233. The City of Glendale’s 2025 figures average 237 ppm. Both averages are over Rinnai’s limit.

Rinnai’s tech sheet says “Hard water must be treated to prevent scale build up or damage to the heat exchanger.” Rinnai’s manual adds, “Damage caused by lime build-up is not covered by the unit’s warranty.” Rinnai’s flush runs undiluted white vinegar through the heat exchanger, and its flushing page says to flush “at least once a year” and to “Never use chemical solutions of any kind.” Our Service Agreement includes a yearly visit with the water heater flush. See a tankless maintenance visit in Buckeye.

A water softener takes most of the hardness out before water reaches the heater, so less scale forms in the first place. Whether to add one is your call, and we’re glad to give you an estimate. See our water softener options.

Can You Replace a Rinnai Heat Exchanger Yourself?

Not by Rinnai’s rules. Its warranty says “All repair parts must be genuine Rinnai parts” and that repairs “must be performed by a qualified professional who is properly trained to do the type of repair.” The job means working on gas and water parts inside a cabinet packed with wiring, then setting the gas pressure with a manometer and leak-testing every gas joint.

You can still do the first steps yourself: shut off the water, power and gas, and take a photo of the heater’s rating plate, the label with its model and serial number.

Questions Homeowners Ask About a Rinnai Heat Exchanger Leak

Is a Rinnai warranty transferable if you bought the house with the heater in it?

Usually, yes. Rinnai’s Value Series warranty covers “subsequent owners,” as long as the heater stays where it was first installed. You’ll need proof of purchase, such as a registration within 30 days of purchase. For a heater that came with a new home, Rinnai can verify the registration with the first buyer’s closing papers.

Can a leaking Rinnai heat exchanger be patched?

It shouldn’t be. Rinnai lists the heat exchanger as a replacement part, its warranty says repair parts must be genuine Rinnai parts, and its manual warns that any alteration to the appliance or its controls can be dangerous and will void the warranty. Replacing it is the fix, and that’s what Pridemark Plumbing did on this May 2026 job.

Does Rinnai’s warranty cover the labor on a heat exchanger repair?

Only in the first year on Value Series heaters: Rinnai lists 1 year of reasonable labor for a home, against 10 years on the heat exchanger, from the date of purchase. On our May 2026 repair, Rinnai’s warranty covered the parts, and we told the homeowner what the rest would cost before we started.

Is Glendale’s water too hard for a tankless water heater?

Often, by Rinnai’s standard. Rinnai’s manual sets a 200 mg/L (200 ppm) hardness limit for its V-series heaters. In 2025, Glendale city water averaged 237 ppm, and Liberty Utilities’ Litchfield Park system listed a highest average of 233. Rinnai says hard water must be treated, so a softener and a yearly flush help protect the heat exchanger.

How long does a Rinnai heat exchanger repair take?

It depends on the part and the warranty case. When Pridemark Plumbing replaced a leaking Rinnai heat exchanger in May 2026, the call came in on May 4, the new heat exchanger was in by early afternoon on May 5, and the hot water was back that day. Until the repair’s done, keep the water, power and gas off if it’s still leaking.