Quick answer: Most tankless water heater problems in Richardson, Frisco, Denton, and across DFW come from mineral scale in the heat exchanger, ignition or gas supply issues, clogged inlet filters, or venting problems. The majority can be repaired, often with descaling and part replacement. A tankless unit that’s properly maintained can last 20 years, so repair is usually worth it unless the heat exchanger has failed on an older unit.
Why Tankless Units Need Repair in North Texas
A tankless water heater heats water instantly as it passes through a narrow heat exchanger. That design is efficient, but it’s sensitive to hard water. North Texas water carries enough calcium and magnesium to coat those passages with scale. As scale builds up, the unit overheats, loses flow, and eventually throws an error code or shuts down.
If you’re still deciding whether tankless is right for your home, start with our complete tankless water heater guide. This post is for homeowners whose tankless unit is already acting up.
Common Tankless Problems (and What They Usually Mean)
Error code on the display. Every brand uses its own codes, but they fall into a few families:
Ignition or flame failure (for example, Navien E003): gas supply, igniter, flame rod, or venting
Scale or lime warnings: the heat exchanger needs descaling
Overheat codes: often scale restricting flow
Fan or vent codes: a blocked intake or exhaust, or a failing combustion fan
Write the code down before you call. It speeds up diagnosis and helps our technician bring the right parts.
Hot water fluctuates or turns cold mid-shower. This can be a partially clogged inlet filter, scale buildup, or a flow rate too low to keep the burner lit. It’s also sometimes a mixing valve or fixture problem rather than the heater itself.
Unit won’t fire at all. Check that the unit has power, that the gas valve is open, and that nothing is blocking the vent. If all three check out, the likely causes are the igniter, flame rod, or control board.
Not enough hot water for multiple showers. The unit may be undersized, or the gas line may be too small to feed it at full output. This is a common issue after DIY or builder-grade installs.
Water leaking from the unit. Look at the isolation valves, pressure relief valve, and condensate line first. A leak from the heat exchanger itself is more serious.
Descaling: The Repair That Prevents Most Repairs
In hard water areas like Richardson, Frisco, and Denton, we recommend descaling every tankless water heater once a year. Homes with very heavy use or no water softener may need it more often. Descaling involves:
Shutting off power, gas, and water to the unit
Connecting a pump to the isolation valves
Circulating a descaling solution through the heat exchanger
Flushing, cleaning the inlet filter, and checking for proper flow and ignition
Skipping descaling is the #1 reason we see tankless heat exchangers fail early in North Texas.
Repair or Replace Your Tankless Water Heater?
Repair if the unit is under 12–15 years old, or the problem is scale, an igniter, a flame rod, a fan, a sensor, or a board.
Consider replacement if:
The heat exchanger is cracked or leaking
The unit is 15+ years old and needs a major part
Parts are discontinued for your model
The unit was badly undersized from the start
Tankless Repair in Richardson, Frisco, Denton and Across DFW
Lone Star Water Heaters repairs and maintains Navien, Noritz, Rheem, A.O. Smith, and other major tankless brands. We serve Richardson, Frisco, Denton, Plano, Carrollton, and the full DFW metro.
24/7 emergency service and same-day appointments
Fully stocked trucks for one-visit repairs
Family- and veteran-owned, licensed (RMP 42483)
Water heaters only, so tankless diagnostics are a core skill for us, not a side service
Tankless Water Heater Repair FAQs
How often should a tankless water heater be descaled in North Texas?
At least once a year. Hard water across DFW builds scale in the heat exchanger faster than in soft water areas.
Why does my tankless water heater show an error code?
Most codes point to ignition, scale, overheating, or venting. Write the code down and call a technician. Repeatedly resetting the unit can hide a gas or venting problem.
How long do tankless water heaters last?
Up to about 20 years with regular descaling. Units that are never descaled often fail much earlier in hard water areas.
Do you repair tankless water heaters in Richardson and Frisco?
Yes. We offer same-day tankless repair throughout Richardson, Frisco, Denton, Plano, and all of DFW.
Call 888-844-8105 or visit www.lonestarhotwater.com for tankless water heater repair.