How a tankless water heater works
When you open a hot tap, a flow sensor tells the unit that water is moving. The burner or elements fire, and the heat exchanger raises the temperature as the water passes through. Close the tap and the unit shuts down, so nothing is kept hot between uses.
Every unit has a maximum temperature rise at a given flow rate. Ask for more hot water than it can heat, say two showers and a dishwasher at once, and the temperature drops. That limit explains a lot of complaints that are not faults at all.
Signs your tankless unit needs attention
Start with what you notice at the tap. The pattern usually tells us where to look first.
Slow to heat
Hot water takes a long time to reach a far bathroom. Some of that wait is cold water already sitting in the pipe, but a scaled exchanger or a clogged inlet screen can add to it.
Temperature swings
Hot, then lukewarm, then hot again, often when a second fixture opens. Flow limits, a weak flow sensor, scale or a gas supply that is too small can all cause this.
The cold water sandwich
A burst of hot water, a short cold stretch, then hot again after you pause a shower. It is a known tankless habit and sometimes improved with settings or a recirculation setup.
An error code on the display
Codes usually point to ignition, flame sensing, venting or flow. Write the code down, because the manual and the unit's error history narrow the cause quickly.
Weak hot flow only
Cold water runs normally but hot is thin. A partly blocked inlet filter screen or heat exchanger is the usual suspect.
Rumbling or popping
Scale can make water boil in small pockets inside the exchanger. That sound is a descaling conversation, not a reason to ignore the unit.
Damp spots at the unit
Leaks at a union, a service valve or the condensate line leave moisture below the heater. Shut the unit off and take a photo before you call.
If you smell gas or see water pouring from the unit
A gas smell means leave the building and call the gas utility or 911 from outside. Do not flip switches or look for the source. We come after the gas company says the home is safe.
For a steady leak, turn off the gas or power to the unit, then close the cold-water isolation valve below it. If that valve is missing or will not turn, close the main water shutoff, usually where the line enters the house.
Planning tankless water heater work?
Call for a clear price before work starts, and ask about same-day appointments when available.
Why winter changes tankless performance in Zionsville
NWS climate normals for Indianapolis, the nearest long-term station, give a January average low of 20.9 F. Water entering a house in winter is usually colder than in summer, so the unit must add more heat to reach the same setting. A shower that stays hot in July can run lukewarm in January at the same flow.
If that matches your house, ask us to compare the unit's maximum temperature rise with the flow of your fixtures. Also check where the unit sits. Most tankless heaters rely on electrical freeze protection, so one in an unheated garage or crawl space can freeze during a power outage in a hard cold snap. Your manual lists the rules for your model.
How we find why a tankless unit underperforms
We start with the display history and the code table in the manual. Then we check the basics in order. That means the inlet filter screen for debris, hot and cold flow at a fixture, gas pressure on a manometer while the unit fires, and the vent and combustion air path.
A flow sensor or temperature sensor that reads wrong gets tested before it is replaced. If the heat exchanger looks scaled, we confirm with flow and temperature rise readings, then talk through descaling. You hear what we found before any parts are ordered.
Flushing and descaling a tankless water heater
Minerals come out of the water when it is heated, and the narrow passages of a tankless heat exchanger collect them as scale. The early signs are longer waits for hot water, lower flow, noise and error codes. Flushing pushes a manufacturer-approved descaling solution through the exchanger so those deposits dissolve and rinse away.
A proper flush needs isolation valves with drain ports on the hot and cold lines, plus a small pump and hoses. Many units were installed without them, and we can add the valves during the same visit. We also clean the inlet screen, because debris there looks like scale at the tap.
How often to flush depends on your water and your maker's manual. Your water bill names your utility, and its annual water quality report lists hardness. You can also test your tap with a kit from a hardware store. If the water is hard, softening or filtration ahead of the heater can slow scale, though that is a separate decision.
Descaling has limits. It cannot repair a cracked exchanger, a failed circuit board or a leaking fitting, and a unit that has gone years without a flush may not recover fully. We tell you which case you are in.
Repair, descale or replace
The right move depends on what failed and how old the unit is. This is how we usually sort it.
| What you see | What we usually do | Honest trade-off |
|---|---|---|
| Slow heat, noise, low hot flow | Clean the inlet screen, flush and descale | Works only if the exchanger is intact, and it may need repeating |
| Ignition or flame error codes | Test the igniter, flame sensor and gas pressure | A gas line that is too small brings the code back |
| Hot and cold swings | Test the flow and temperature sensors, review fixture flow | Sometimes the unit is simply sized below your demand |
| Leak at a union or valve | Replace the fitting or valve | A leak from inside the exchanger usually means replacement |
| Older unit with repeat failures | Compare repair cost with a new unit | A newer model can bring venting or gas updates |
Repair makes sense when the failed part is small compared with the unit's remaining life. The US Department of Energy lists tankless heaters at about 20 years, so a mid-life unit with one bad sensor is usually worth fixing. Past that age, or with a cracked exchanger, we will say so plainly.
Tankless or tank, an honest comparison
Tankless is a good fit for some houses and a poor one for others. We cannot promise savings on your bills, because they depend on how much hot water you use and what your fuel costs.
What tankless does well
- DOE lists about 20 years of life, against 10 to 15 for tank models
- No stored tank to keep hot between uses
- Wall-mounted, which frees floor space
- Hot water does not run out during one long shower
What to weigh before switching
- Gas models often need a larger gas line and special venting
- Installation work is bigger than a like-for-like tank swap
- Output is limited when many fixtures run or the incoming water is cold
- Units need periodic flushing, and savings are not guaranteed
What a tankless installation involves
A gas tankless unit draws far more gas at full fire than a tank heater, so the existing gas line is often too small. We size it from the unit's gas input and the length of the run, which can mean new pipe from the meter. Venting is the other big item, since many units need sealed vent runs to the outside, and condensing models drain acidic condensate that needs a proper disposal path.
Electric tankless units pull heavy current and may need a dedicated circuit, which is licensed electrician work. Permit rules vary, so ask the Zionsville Planning & Building Department before work starts. If you are swapping a tank for a tankless, our water heater installation page covers the planned-install side, and plumbing installation covers new gas and water lines.
What affects the price of tankless water heater work
Tankless jobs vary more than almost any plumbing work, so we quote after we see the house.
Repair or installation
A descale or sensor swap is a service visit. A new unit adds the heater, the labor to set it and the removal of the old one.
Gas line size
If the run from the meter cannot feed a tankless unit at full fire, the line has to be upsized.
Venting and condensate
Vent material, run length and where the condensate drains all change the scope.
Isolation valves
Adding service valves lets the unit be flushed, and it adds a little to the first visit.
Access and location
A unit in an open utility room is simpler than one in a tight closet or an unheated garage.
Standard homeowner policies usually cover sudden and accidental water damage, such as a burst pipe, and usually do not cover gradual leaks, wear or the failed part itself. Check your policy and ask your agent.
Call us and we will give you a clear price for your unit and your house before work starts.
Call (317) 740-1302Who should work on your tankless heater
Indiana licenses plumbing contractors and journeyman plumbers, and the state's online license verification lets you look up anyone who offers to open a gas appliance. Do it for us too. We are licensed and insured, and we give a clear price before work starts.
We do not promise energy savings, and we will tell you if your gas supply or vent path makes tankless a poor fit. If a tank is the better answer, our water heater replacement and water heater repair pages cover it. We serve Zionsville and nearby towns, and neighboring Whitestown in Boone County.
Frequently asked questions
Follow the schedule in your maker's manual, and shorten it if your water leaves white crust on fixtures. Your utility's annual water quality report lists hardness, and a store-bought test kit checks your tap directly.
A unit that has never been flushed is worth checking now, since scale builds quietly.
Often the delay is cold water already in the pipe between the heater and the tap. A scaled exchanger, a clogged inlet screen or a unit working near its limit in winter can make it longer. We measure flow and temperature rise to tell which one it is.
Codes differ by brand, but most point to ignition, flame sensing, venting or flow. Write down the code and when it appears, then check the manual's table. Some codes clear with a reset, and repeat codes need testing of the part behind them.
Some homeowners with isolation valves already installed do a flush with a pump and the maker's approved solution. It is a gas or electric appliance, so never alter the vent, gas line or controls yourself. If the unit lacks valves or has error codes, call a licensed plumber.
We cannot promise that. Savings depend on how much hot water you use, your fuel cost and what the installation requires. The US Department of Energy lists tankless heaters at about 20 years of life, which is longer than a tank, but upfront work can be larger.
Often yes, but it is more than a swap. We check the gas line size, the vent path, the electrical needs and the space. Permit rules vary, so ask the Zionsville Planning & Building Department about your project.
Yes. We serve Zionsville and nearby towns, including Whitestown, and the same checks apply there. If a leak or gas smell cannot wait, our 24/7 emergency line is open any time.