Tankless Water Heater Repair or Replace? 5 Questions That Settle It
Whether to put money into the old unit or buy a new one is the question nearly every owner with a failed tankless asks. Tankless water heater repair or replace comes down to the same five questions, and the honest answer is that most faults are repairs: the parts can be replaced and scale can be cleaned off. The exception is a heat exchanger that has started to leak on an older unit.
Prices below are estimates, not quotes. A technician finds the fault first and agrees the price in writing before work starts. To have the fault found, get a technician out.
1. What exactly failed?
Flow sensors, igniters, flame rods, thermistors, fans, gas valves and circuit boards are all replaceable parts, and scale is cleaned out by descaling. The heat exchanger is the one expensive part. A fault code on a unit that was never flushed is often a descale first, not a replacement.
The estimated ranges to keep in mind: a diagnosis visit at $100 to $250, a descale at $150 to $350, part repairs at $150 to $800 and a heat exchanger replacement at $1,000 to $2,500.
2. How old is it?
Gas tankless units commonly last 20 years or more with maintenance, and some manufacturers put it at 15 to 20. Electric tankless units commonly last 7 to 10. A part failure at six years is a repair. The same part at 18 years on a gas unit, or at nine on an electric one, is worth weighing against replacement, because the next failure is closer. The data plate has the model and serial number, which you will want for any warranty question.
3. What does the warranty cover?
Heat exchanger warranties commonly run 12 to 15 years and parts around 5, and they depend on registration and maintenance. Some makers cover their stainless exchangers for 15 years in a home. Labor is a different matter: owners report that a warrantied exchanger can still leave a large labor bill. A maker can also ask whether the unit was descaled, so the dates of your flushes matter. Check the model and serial number against the warranty before you decide.
4. How do the two sets of numbers compare?
A heat exchanger replacement is estimated at $1,000 to $2,500. A new unit installed is estimated at $2,500 to $5,500, included here for context. On an older unit, an exchanger quote that approaches the low end of that range is the point to ask for a replacement price too. One owner was warned that after an exchanger replacement on an old unit you can see one small part failure after another.
A swap can also change the price. Most tankless units need a larger gas line than a tank heater, commonly 3/4 inch, and a like-for-like replacement is simplest when the gas line and venting are already right. Ask for both quotes in writing.
5. Why did it fail, and will it happen again?
Water quality is the usual reason a heat exchanger leaks: an owner who lost two exchangers in four years was told so. If scale, or a unit installed without service valves, caused the failure, a new unit on the same water is likely to repeat it. Flushing on schedule (see how to flush a tankless water heater), service valves, and a scale filter or a softener are what change that. Fix the cause whichever way you decide.
Home warranty and homeowners cover
If you have a home warranty plan, call it before paying for any work, because some plans send their own technician and some ask for proof of yearly flushes. Homeowners insurance is a separate thing again: read your policy to see how it treats appliance wear compared with water damage.
The short version
A part fault on a young unit is a repair. A scale code on a unit that was never flushed is a descale first. A heat exchanger leak on a unit near 20 years, or a repair quote close to the price of a new unit, is the moment to price a replacement as well. If the fault is a leak, the leak guide helps you tell which source you have, and the guide to codes helps if the unit is showing one.
Quick answers
Can a tankless water heater be repaired?
Yes, in most cases. Igniters, flame rods, flow sensors, thermistors, fans, gas valves and boards can all be replaced, and scale can be descaled. A leaking heat exchanger on an old unit is the main exception.
How much does it cost to fix a tankless water heater?
Most part repairs are estimated at $150 to $800 and a descale at $150 to $350, plus an estimated $100 to $250 for the diagnosis visit.
How much does it cost to replace a heat exchanger on a tankless water heater?
A heat exchanger replacement is estimated at $1,000 to $2,500. A warranty can cover the part but not always the labor.
What is the lifespan and the average warranty of a tankless water heater?
Gas units commonly last 20 years or more with maintenance, and electric units 7 to 10. Heat exchanger warranties commonly run 12 to 15 years and parts around 5.
Can a plumber fix a tankless water heater?
Many licensed plumbers can, especially for flow, leaks and valves. Codes and gas faults go better with a technician who works on tankless units often, so ask whether they work on your brand.
Still no hot water?
A technician who works on tankless units can test it and price the fix in writing.
