Residential plumbing ยท Denver Metro, Colorado
Tankless water heater repair and descaling
Most tankless problems, like error codes, ignition failures, temperature swings and low flow, trace back to scale in the heat exchanger, a clogged inlet filter, gas supply or venting. Descaling through the isolation valves fixes many of them and should be done periodically anyway.
Tankless heaters are reliable when they're maintained and sized right. When they act up, the unit usually tells you something through an error code on the display. That code plus a few questions about what you're seeing gets most diagnoses started.
Common problems
- Error codes and ignition failures: often gas supply, venting or flame sensing issues.
- Hot and cold swings: scale, a dirty filter, low flow below the unit's minimum, or a sizing problem.
- Reduced flow or pressure: clogged inlet filter or scaled heat exchanger.
- Unit shuts off mid-shower: flow dropping below the activation threshold, overheating from scale, or venting faults.
- Noise: scale can cause kettling sounds in the heat exchanger.
Descaling, step by step
With the unit off and the isolation valves closed, a small pump circulates a descaling solution (often food-grade vinegar or a manufacturer-approved product) through the heat exchanger for the time the manual specifies. Then it's flushed with fresh water, the inlet filter is cleaned, and the unit is restarted and tested. Without isolation valves, they need to be added first.
How often
It depends on your water hardness and how much hot water you use. Manufacturer manuals give intervals, and many units display a maintenance reminder. Hardness varies widely across the metro by provider; your utility's annual water quality report lists it.
Repair or replace?
Most tankless parts are replaceable: igniters, sensors, fans, control boards and valves. A cracked heat exchanger on an older unit is the main reason replacement comes up. The U.S. Department of Energy notes most tankless heaters last more than 20 years, so a repair is usually worth considering.
Signs of scale buildup
- Hot water takes longer to reach temperature or never quite gets there
- Flow at the hot tap drops over time
- Rumbling or kettling sounds while the burner runs
- Scale or overheat error codes
- The maintenance reminder is lit
Keeping scale down
Scale forms faster at higher temperatures, so setting the unit no hotter than you need helps. Clean the inlet filter screen when you descale. Follow the manufacturer's interval for your water hardness; your provider's annual water quality report gives the hardness figure. If the unit was installed without isolation valves, adding them makes every future descaling quicker and cheaper.
Signs your tankless needs service
- An error code on the display
- Water turns cold in the middle of a shower
- Reduced hot water flow
- Unit won't fire
- Maintenance reminder showing
- It hasn't been descaled in years
How a visit goes
- Read the codeAnd ask what's been happening.
- Check gas, venting and flowThe usual causes first.
- Descale and cleanHeat exchanger and inlet filter.
- Repair parts if neededThen test under real demand.
What's different here
- Cold incoming water. Winter supply water is much colder, which lowers a unit's flow at a given temperature. Size for winter.
- Altitude. Follow the manufacturer's altitude settings or derating.
- Hardness varies. Some metro providers deliver harder water than others, which changes how often a unit needs descaling.
What affects the cost
Every home is set up differently, so we price the job after we've seen it. These are the things that move the number.
- DiagnosisError codes narrow it down quickly.
- PartsSensors are small; control boards and fans cost more.
- DescalingEasier with existing isolation valves.
- Adding valvesIf the original install skipped them.
- Venting fixesSome faults are vent-related.
- Unit ageOlder units may have discontinued parts.
Questions we hear
How do I know if my tankless needs descaling?
Reduced flow, temperature swings, kettling noise or a maintenance reminder on the display are common signs.
Can I descale a tankless water heater myself?
With isolation valves, a pump and the manual, many homeowners do. If the unit has no isolation valves, they need to be installed first.
Why does my tankless shut off during a shower?
Flow can drop below the unit's minimum, scale can trigger overheating protection, or there's a venting or gas issue.
What do tankless error codes mean?
Each manufacturer has its own list in the manual. Tell us the brand and code and we can usually narrow it down on the phone.
Is it worth repairing an older tankless unit?
Usually, if the heat exchanger is sound. Most parts are replaceable.
Do you service brands you didn't install?
Call with the brand and model and we'll tell you straight whether we can help.
Does a lower temperature setting reduce scale?
Yes, generally. Scale forms faster at higher water temperatures. Set it as low as your household comfortably needs.
What happens if I never descale my tankless?
Scale insulates the heat exchanger, reduces output and flow, and can trigger overheat errors. Over time it shortens the unit's life.
Can scale damage a tankless water heater permanently?
Heavy, long-term scale can overheat and stress the heat exchanger. Regular descaling prevents most of that.
Why does my tankless show a flow or ignition error?
Common causes are a clogged inlet filter, gas supply problems, venting obstructions or a failing igniter or flame sensor. The error code narrows it down.
How long does descaling take?
Usually around an hour of circulation plus setup, flushing and testing, depending on the manufacturer's instructions and how scaled the unit is.
Related services
Water Heater Repair & Replacement
Tank water heaters that leak, run out of hot water or won't light. Repaired when it makes sense, replaced when it doesn't.
Tankless Water Heaters
Wall-mounted tankless installs sized for Colorado winters, plus repair and descaling for the units you already have.
Tankless water heater repair and descaling near you
We're based in Thornton and work across the Denver Metro:
Emergency plumber by city
Water leaking now? Shut off the main, then call.
Something leaking, dripping or cold?
Call and tell us what's going on, or pick a time online. If it's not something we handle, we'll say so.