Tankless Water Heater Repair in Austin, TX
- Licensed Texas plumbers
- Gas and electric, tank and tankless
- Same-day visits when the schedule allows
Reading the error code before anything gets replaced
A tankless heater tells you what it thinks is wrong, and the display or flashing LED is the starting point. Codes differ by brand and model, so the manual is the authority, but on many Rinnai and Noritz units a 10 points to an air supply or exhaust problem, 11 means the burner did not ignite, 12 means the flame went out, and 16 is an over-temperature fault.
Those codes describe symptoms, not parts. A code 11 might be a closed gas valve, a gas line too small after a regulator change, a dirty flame rod, a failed igniter or a blocked vent, and a technician who replaces the first part on the list can spend an afternoon on the wrong one.
Common tankless faults and what they cost to fix
The figures are typical Austin-area ranges for 2026 and not quotes. They assume a unit under about twelve years old, and a part that is still available.
| Symptom | Likely cause | Typical cost |
|---|---|---|
| Water turns lukewarm or fluctuates | Scale on heat exchanger, clogged inlet filter, failing flow sensor | $150 – $450 |
| Error 11, no ignition | Gas off or restricted, dirty or failed flame rod, igniter, vent blockage | $200 – $600 |
| Error 12, flame lost mid-use | Gas pressure drop, condensate trap blocked, dirty burner | $200 – $550 |
| Error 10 or vent code | Blocked or disconnected vent, bird nest, inadequate combustion air | $150 – $500 |
| Heater fires only at high flow | Flow sensor or water turbine clogged with scale | $180 – $450 |
| Hot water slow to arrive or cold sandwich | Normal tankless behaviour, or a faulty recirculation pump or check valve | $200 – $700 |
| Leak from the unit | Failed water connection, heat exchanger crack, condensate leak | $250 – $1,800 |
| Heat exchanger replacement | Cracked or scaled through | $900 – $2,000 |
What Austin water does to a heat exchanger
Austin Water reports total hardness averaging about 5.4 grains per gallon across 2025, with samples ranging from roughly 4.1 to 7.4, from a Colorado River supply that passes through Lake Travis and Lake Austin. That water is moderately hard, and a tankless heat exchanger is a narrow, hot passage where dissolved minerals come out of solution as scale.
The signs build slowly: reduced flow, temperature swings at low volume, a unit that shuts down on overheating, and error codes that clear when the power is cycled. Private wells in the Hill Country around Dripping Springs and western Hays County can be harder still, and a unit on well water without conditioning often needs descaling every six months instead of every year.
A descale visit, step by step
Descaling is the most valuable thing a tankless owner can do, and it works only if the installation included isolation valves with flush ports.
- Turn off the gas at the shutoff and cut power to the unit.
- Close the hot and cold isolation valves and open the flush-port caps.
- Connect hoses and a small pump to the two ports, creating a closed loop through the heat exchanger.
- Circulate white vinegar or a manufacturer-approved descaling solution for 45 to 60 minutes.
- Flush the loop with clean water until the discharge runs clear, then clean the inlet filter screen.
- Reopen the valves, restore gas and power, and test a hot tap at low and high flow for temperature stability.
Gas supply faults that look like heater faults
Tankless units need far more gas at once than tank heaters, and a fault in the supply shows up as an ignition error. Rinnai's bulletin on gas line sizing notes that most of its models call for three-quarter-inch pipe, with half-inch workable only on short runs at adequate pressure, so a house with a half-inch line installed in the 1990s can start throwing flame errors when other gas appliances run at the same time.
Texas Gas Service delivers gas across most of Austin, and a pressure check at the heater while the furnace or range is running separates a supply problem from a failed part. A smell of gas is not a repair question: leave the house and use the gas company's emergency line from outside.
Freeze damage and exterior units
Outdoor tankless units on Austin homes were exposed to the freezes of February 2021, January 2023 and January 2024. Most models carry built-in freeze protection, but it depends on electrical power, so an outage at the wrong moment leaves the water inside the heat exchanger and condensate lines unprotected.
After a freeze, look for water at the bottom of the case, a drip from the condensate line, or low flow that does not recover once temperatures rise. A cracked heat exchanger is not a DIY repair. The freeze protection guide lists what to insulate and when to drain.
Repair or replace a tankless unit
A well-kept tankless heater can last fifteen to twenty years, and a repair is nearly always right while the heat exchanger is sound. The line moves when a unit is past fifteen years, the heat exchanger itself is cracked or badly scaled, or a main board or fan has failed on a discontinued model.
A new gas tankless replacing an old one typically costs $3,200 to $5,800 installed when the venting and gas line are reusable, so a repair above about $1,500 on a unit past ten years is hard to justify. The cost of a first install is on the tankless installation page, and routine upkeep, including yearly flushes, is part of water heater maintenance.
Straight answers
How do I fix a tankless water heater that is not working?
Check the display for an error code, confirm gas and power are on, clean the inlet filter, and look for a clogged vent or frozen condensate line. If the code returns, a descale or a technician is the next step. Do not open the gas side or the combustion chamber yourself.
Why does my tankless water heater keep going cold in the shower?
A cold burst usually comes from low flow below the minimum needed to fire the burner, scale on the heat exchanger or flow sensor, or an undersized gas line. Hard water causes a lot of this. A descale often fixes it, and a recirculation loop helps the delay at the tap.
How much does tankless water heater repair cost in Austin?
Most repairs run about $150 to $600 in the Austin area, with descaling at roughly $150 to $350. Replacing a heat exchanger or main board can reach $900 to $2,000. These are typical 2026 ranges, and the age of the unit decides whether the repair is worth doing.
How often should a tankless water heater be flushed in Austin?
Once a year on city water is the usual advice, since Austin Water averages about 5.4 grains per gallon. Homes on private wells or with very hard supply may need it every six months. Skipping flushes is the main cause of reduced flow and overheating codes.
Does a tankless heater need maintenance?
Yes. Annual descaling, a clean inlet screen, an inspected vent termination and a check of the condensate drain and neutraliser keep most units trouble-free. Gas models also benefit from a combustion check. Neglect shows up as error codes, lukewarm water and shorter life.
What does error code 11 mean on a Rinnai?
Code 11 means the heater did not ignite when it called for heat. Typical causes are a closed gas valve, weak gas pressure, a fouled sensor or igniter, or an obstructed vent. Other brands use different numbers, so the model's manual is the reference.
Water heater trouble around Austin?
Give your ZIP and the symptom, and the call handles the rest.