Tankless water heater repair means finding and fixing the part that’s failed, such as the igniter, a sensor, the circuit board or the heat exchanger. HomeGuide says minor repairs average $50–$300, while bigger repairs run $300–$1,300. The heater’s error code is usually the most useful first clue, and some codes point to scale that a flush can clear rather than a broken part.
Repair costs by part
HomeGuide’s maintenance cost guide lists these averages for common tankless repairs:
| Repair | HomeGuide average |
|---|---|
| Minor repairs | $50–$300 |
| More extensive repairs | $300–$1,300 |
| Heat exchanger replacement | $600–$1,300 |
| Circuit board replacement | $400–$800 |
| Burner or heating element replacement | $400–$800 |
| Pressure relief valve replacement | $80–$150 |
Labor is part of every line. Angi says plumbers charge $45–$200 per hour, depending on experience. A diagnosis that takes longer, or a part that has to be ordered, adds to the bill. The technician sets the final price.
What usually fails, and the codes that point to it
Error codes are how the heater’s control board reports a problem. Here are the common failure groups, with the codes manufacturers tie to each.
The burner won’t light
The heater senses water flow but can’t light or keep a flame. Rinnai lists code 11 as no ignition (the heater is not turning on) and code 12 as no flame. Navien uses E003 for ignition failure and E012 for flame loss. Noritz lists code 11 as ignition failure, and Takagi’s code 111 is also ignition failure. Causes include gas supply, the igniter, the flame sensor and the gas valve. On a Rheem RTGH, code 11 can mean the gas shut-off valve is not fully opened. These are gas-side faults, and a technician should handle them.
Air, exhaust and combustion faults
A blocked intake or vent stops the burner from running safely. Rinnai’s code 10 is an air supply or exhaust blockage. Takagi’s code 991 is imperfect combustion. Noritz code 90 covers a possible blocked air supply or exhaust vent, abnormal combustion, or a clogged condensate drain. Vent work is for a technician only.
Overheating
When the heat exchanger or its outlet runs too hot, the heater shuts itself down to protect itself. Rinnai’s code 14 means the heat exchanger has overheated, and its manual says to check for hot spots from scale. Navien’s E016 means the heat exchanger is overheating, with a flush listed among the fixes. Bosch’s E9 means the temperature limiter has sensed over 220 F, which may indicate scale build-up in the heat exchanger. These codes are worth a flush before anyone replaces parts.
Sensors and the circuit board
Bosch’s A7 indicates a problem related to the outlet hot water temperature sensor. Navien’s E515 is abnormal operation of the PCB (circuit board). Board faults are one of the pricier repairs on HomeGuide’s list. A technician should rule out wiring, power supply and water damage first.
Flow problems
Rheem’s P1 means there is not enough water flow to operate the unit. Takagi’s code 651 is a flow adjustment valve fault, and Takagi’s manual lists a motor drive locked by scale among the causes. A clogged inlet filter or scale in the heat exchanger can cut flow too, which is flush territory.
Leaks
Rinnai’s code 79 means a water leak has been detected. Its manual says to turn off the water supply and contact a licensed professional. A leak inside the cabinet can come from a fitting, a cracked heat exchanger or a relief valve.
The error code hub puts the scale and flow codes for all major brands in one table. Brand pages go further: Navien, Rinnai, Noritz, Rheem, Takagi and Bosch.
When the fix is a flush
Scale causes a share of the calls that sound like repairs. Navien’s E030, exhaust overheating, lists cleaning the inlet filter and flushing the heat exchanger as remedies. Bosch’s E1 means the hot water sensor is reading above 185 F, possibly due to scale build-up. A technician who sees these codes on a heater that hasn’t been descaled in a while will usually start with a flush and descale. That’s cheaper than a part and often clears the code.
Repair or replace?
Tankless heaters last a long time when they’re looked after. The Department of Energy says most have a life expectancy of more than 20 years, and HomeGuide says 15 to 20 years. Compare that with 10–15 years for tank heaters.
Use these points to weigh it up:
- Age. A heater well short of its expected life is usually worth repairing, even for a big part.
- What failed. Sensors, igniters and valves are routine. A heat exchanger at $600–$1,300 is a bigger decision.
- Why it failed. Rheem’s warranty says damage caused by lime, mineral build-up, or scale is excluded, and other brands say much the same. A scale-damaged heat exchanger is usually your cost, not the manufacturer’s.
- What a new one costs. HomeGuide puts a tankless heater with installation at $1,400–$5,600.
The lifespan guide covers replacement timing. If replacing wins, the installation page covers costs and the ThermWise rebate.
What a technician checks
A good diagnosis follows the code, then confirms it. Expect the technician to:
- read the current code and ask what you’ve seen before
- confirm gas supply and pressure at the heater
- inspect the intake and exhaust vents for blockage or damage
- check water flow, the inlet filter and the isolation valves
- test the sensors and look for signs of scale or overheating
- look for leaks inside the cabinet and at the fittings
Utah sets rules on who does this work. Even under the state’s handyman exemption, work on a plumbing system must be done by a licensed electrical or plumbing contractor, and repairing a residential gas appliance requires certification under Subsection 58-55-308(2). The Utah licensing guide explains this and points you to DOPL. Ask the technician about their license when you book.
Before you call
Write down the exact code, including whether it flashes or alternates with the temperature. Note what was running when it appeared. Check whether other gas appliances in the house work. If there’s no hot water at all, the no hot water page lists safe checks. Leave the cover on. If you smell gas, leave the house and call your gas utility from outside.
Call to Book a Flush or a repair visit with a technician who works in your area, whether that’s Lehi, Provo, Draper or West Jordan.