Symptom, likely cause and who fixes it
Error codes differ by brand, so the manual's code table is the only reliable translation. These are the general families.
| Symptom | Likely cause | Try this | Call a plumber when |
|---|---|---|---|
| Cold or lukewarm water at a low-flow tap | Flow below the unit's minimum firing rate, or a clogged aerator | Open the tap further and clean the aerator | The unit still will not fire at full flow |
| Water hot, then fading in a long shower | Demand exceeds capacity at your temperature rise | Run fewer fixtures at once or lower the set temperature | You suspect the unit is undersized |
| Ignition or flame failure code | Low gas supply, a closed gas valve or a dirty flame sensor | Check the gas shutoff and reset once | The code returns or you smell gas |
| Exhaust, vent or air supply code | Blocked or damaged vent, or a clogged condensate trap | Clear snow, leaves or nests from the outdoor terminal | You see soot or exhaust spilling |
| Reduced flow, rattling or a scale code | Scale on the heat exchanger or a clogged inlet screen | Clean the screen and flush with descaler | The flush does not restore flow |
| Water under the unit | Loose fitting, a failed isolation valve or a condensate line | Shut off the water and snug accessible fittings | Water comes from inside the cabinet |
A code that clears after one reset was probably a passing glitch. A code that comes back is information about a real fault, so stop resetting and start checking.
Flow rate and why a tankless heater goes cold
A tankless unit does not fire until water moves past its flow sensor, typically around half a gallon per minute. A trickle from a clogged aerator can stay under that line, and the burner never lights.
The other limit is capacity. Maximum flow depends on how far the heater must raise the temperature. Water entering at 50 degrees and leaving at 120 is a 70 degree rise. A 199,000 BTU unit at roughly 90 percent efficiency moves about 5 gallons per minute at that rise, which is half of its advertised rate at a gentler rise.
A 2.5 gallon per minute shower plus a dishwasher fill and a running kitchen tap can exceed that, and the heater answers with lukewarm water. Staggering uses fixes this without touching the unit.
Flushing scale with white vinegar
Check your manual first, since some brands name an approved descaler and warranty terms can depend on it.
Power down
Turn off the power switch or unplug the unit, close the gas valve, and close the cold and hot isolation valves.
Connect the loop
Attach hoses to the service ports on both isolation valves. Place a small submersible pump in a 5 gallon bucket and run one hose from the pump to the cold port and one from the hot port back to the bucket.
Add the descaler
Pour in about 3 to 4 gallons of undiluted white vinegar, or the descaler the manufacturer approves.
Circulate
Run the pump for 45 to 60 minutes. Water that turns cloudy or fizzes shows the vinegar is working. In very hard water, repeat with fresh vinegar.
Rinse and clean the screen
Drain the vinegar, flush with clean water for about five minutes, and pull the cold inlet screen to rinse off trapped grit.
Restore and test
Open the isolation valves, bleed air at a hot tap, restore gas and power, then run hot water and watch for the code or temperature problem that started this.
Flushing is maintenance, not a permit job. If the flush does not bring flow back, the heat exchanger may be too far gone, and that is a call for tankless water heater service.
Cold water or a repeating code? Call (385) 488-1892 to book tankless water heater service in Herriman.
Call (385) 488-1892Herriman's water and permit rules, and what they mean for your unit
Herriman's own water page calls local water very hard, with wells at 25 to 60 grains per gallon and Jordan Valley Water Conservancy District supply at 10 to 12. A heat exchanger scales faster on that water than the manufacturer's average-water schedule assumes. Plan a flush at least once a year, and consider a water softener upstream of the heater.
The city moves to its JVWCD-only winter source from mid-October and brings wells back as demand rises in spring. The city also suggests checking softener settings with the season. If you flush once a year, do it in autumn, after the well-blended summer months have left their mineral load behind.
Herriman requires a permit for replacing or adding a water heater and asks for a gas diagram on tankless units. Cleaning, flushing and part swaps count as maintenance. Replacing the unit does not, so call the building department at 801-446-5327 before you swap one.
Herriman's gas utility is Enbridge Gas. If you smell gas, leave the house, then call 911 and Enbridge at 1-800-767-1689 from a safe place. Do not troubleshoot a suspected gas leak.
Gas supply and venting checks that are safe to do
Gas-fired tankless units draw a lot of fuel at once, often 150,000 to 200,000 BTU per hour. A line sized for a tank heater may starve one when another gas appliance is running. Signs include ignition codes on cold mornings or a flame that fades when the stove lights.
You can check that the gas valve is open and that the outdoor vent terminal is clear. You should not alter vent runs, change pipe size or adjust combustion settings. That work needs a licensed plumber or gas technician and often an inspection.
Neighbors follow the same logic. Riverton says work on regulated gas and plumbing systems needs a permit, and Census data shows about 85 percent of occupied homes in West Jordan heating with utility gas.
Hand it off when
Stop troubleshooting and call a licensed plumber in these cases.
- You smell gas, see soot at the vent, or hear a repeated ignition click with no flame.
- The same error code returns after a flush and a fresh reset.
- Water leaks from inside the cabinet or from the heat exchanger.
- The gas line, vent run or unit location needs to change.
- The unit is a decade or more old and failures are stacking up, which is the moment to compare repair with water heater installation of a new unit.
Questions homeowners ask
Does the mid-October water source change affect my tankless heater in Herriman?
Yes, indirectly. The city shifts to its JVWCD-only winter source from mid-October, and that water is softer than the local wells. Scale builds fastest in the well-blended months, so a flush in autumn clears the summer's deposits. If you run a softener, the city advises checking its settings as the source changes.
How often should I descale a tankless water heater?
Manufacturers commonly recommend once a year, and very hard water argues for yearly or more often. A softener upstream can stretch the interval. Watch for slower flow, rattling or a scale code as the signal to flush sooner.
Why do I get a cold burst between hot water?
Water sitting in the pipe cools while the unit is off, so a short pause leaves a cold slug before the heater fires again. Running the tap a few seconds smooths it out.
Can I use vinegar on any brand?
Most brands accept white vinegar for a flush, but some name their own descaler and may tie warranty terms to it. Read the manual first. Never use a stronger acid or any cleaner that the maker does not approve.
Should I repair or replace an older tankless unit?
Well-maintained units often run 15 to 20 years, but a unit with a cracked heat exchanger or repeated failures costs more to nurse along than to replace. A plumber can weigh repair against replacement once the code and the unit's age are known.
What error code means call a plumber?
Any ignition, flame, exhaust or overheat code that returns after one reset and a clean inlet screen. Those point at gas, venting or the heat exchanger, which are not homeowner repairs.
Stuck on an error code? Call (385) 488-1892 for a licensed plumber, or see tankless water heater service.
Call (385) 488-1892Sources and standards
Local rules and figures in this guide come from the public sources below. Fees and codes change, so confirm the current version before you act on it.