Tankless Water Heater Service

Tankless Water Heater Problems

Tankless heaters tell you when something's wrong. An error code on the display, water that turns cold mid-shower, or a unit that won't fire at low flow are the most common signals.

• An error code on the unit's display
• Water that goes from hot to cold during use
• The unit doesn't fire at low flow
• Reduced flow or less hot water in hard water areas

How to Read a Tankless Error Code

Most tankless heaters show a numbered code on the front display when something is wrong. The code points to a specific system, such as ignition, flame detection, venting, water flow or overheating, but the numbers differ by brand, so look it up in the owner's manual or on the manufacturer's website. Write the code down before you call; it often tells the plumber which parts to bring. Repeated flow or overheating codes in hard water areas often point to scale in the heat exchanger.

How Tankless Water Heaters Are Serviced

Service usually starts with the error code, which points to a specific system. Many problems trace back to scale in the heat exchanger, which is cleared by circulating a descaling solution through the unit.

1. Read the error code or diagnose the symptom.
2. Check gas supply or electrical, venting and inlet filters.
3. Descale the heat exchanger if needed.
4. Repair or replace components, then test at several flow rates.

What Affects the Cost of Tankless Water Heater Service

For an existing unit, cost depends on whether it needs descaling, a part or a full repair. For a new install, the gas, venting and electrical work around the unit often costs as much as the heater.

• Repair, descaling or a new installation.
• For a new install: gas line upsizing, new venting or electrical upgrades.
• Unit size, based on how much hot water you use at once.
• Whether service valves for flushing are already installed.

When a Tankless Heater Problem Is Urgent

• You smell gas near the unit.
• The unit is leaking.
• There's no hot water and an error code won't clear.

Descaling Tankless Heaters in Hard Water Cities

Tankless units heat water through a narrow heat exchanger, so scale hurts them faster than tank heaters. In Phoenix (about 10 to 16 grains per gallon), San Diego (about 16) and Indianapolis (about 19 on average), descaling on a regular schedule, and often a softener, keeps a tankless unit from throwing error codes and losing output.

Local plumbing details: Phoenix, San Diego, Indianapolis

Water Hardness by City

What our city pages say about water hardness:

• Joliet, IL: Very hard, about 22 grains per gallon east of Midland Avenue and 12 west of it.
• Spring Valley, NV: Very hard; the Las Vegas Valley Water District reports about 16 to 17 grains per gallon (280 to 291 ppm).
• Mesa, AZ: Very hard, 12 to 22 grains per gallon depending on the water source serving your area.
• Plymouth, MN: Very hard, about 24 grains per gallon.
• Burbank, CA: Very hard, averaging about 16 grains per gallon (2016 report).
• San Antonio, TX: Very hard, typically 15 to 20 grains per gallon.
• St. Joseph, MO: Very hard, about 222 ppm (about 13 grains per gallon).
• Lafayette, IN: Very hard, 19 to 22 grains per gallon.

Before the Plumber Arrives

• Write down any error code on the display.
• Note the brand and model from the unit's label.

Related Plumbing Problems

• No Hot Water: Troubleshooting Gas and Electric Water Heaters
• Water Heater Leaking: Causes and What to Do

Tankless Water Heater Questions