Step-by-Step Guide to Fix Tankless Water Heater Errors

A practical, easy-to-follow guide to help you fix common tankless water heater errors. Learn quick troubleshooting steps to restore hot water fast.

Introduction

Tankless water heaters are known for delivering endless hot water, high efficiency, and long-term reliability. But even the best systems can run into occasional issues—error codes, inconsistent temperature, or the dreaded no hot water situation. Whether you’re dealing with a tankless water heater not heating, unusual error codes, or general performance problems, knowing what to do next can save time, stress, and money.

In this guide, we’ll walk you step-by-step through how to fix tankless water heater issues, understand common error codes, and perform basic tankless water heater troubleshooting safely and effectively.

Why Tankless Water Heaters Stop Working

Before diving into repairs, it helps to know what causes tankless water heater problems. Some of the most common reasons include:

Mineral buildup from hard water
Low water pressure or flow restrictions
Gas supply issues (for gas models)
Electrical problems (for electric units)
Blocked air intake or exhaust vents
Ignition or flame sensor failure
General lack of tankless water heater maintenance

Understanding the cause helps you determine the right fix and avoid recurring issues.

Step-by-Step Guide to Fix Tankless Water Heater Problems

1. Check for Error Codes

Modern tankless units display error codes that point to the issue. Common tankless water heater error codes include:

Error 11/12 – Ignition failure
Error 16 – Overheating
Error 29 – Condensation problem
Error 61 – Fan motor failure
Error 99 – Combustion issue

Look up your brand’s code chart (Rinnai, Navien, Noritz, Takagi, Bosch, etc.). If you can’t find it, check the manual or manufacturer website.

Fixing tip:
Reset the unit after reading the code. If the code returns, follow the repair steps below.

2. Confirm Water Flow

A tankless water heater needs steady water flow to activate.

Check for:

Closed or partially closed supply valves
Clogged aerators, showerheads, or filters
Frozen pipes (in winter)

Fix:
Open all valves fully, clean aerators, or thaw pipes if needed.

3. Inspect for Mineral Buildup

Hard water is a major cause of tankless water heater not heating properly.

Signs of scale buildup:

Temperature fluctuation
Reduced water flow
Rumbling or hissing noises
Frequent error codes

Fix:
Flush your tankless water heater using a pump, two hoses, and vinegar or descaling solution. For best results, professional flushing once a year is recommended—especially in Michigan’s hard-water regions.

4. Check the Gas Supply (Gas Models)

Gas issues are one of the most common reasons tankless water heaters stop working.

Check:

Is the gas valve fully open?
Do other gas appliances work?
Is the gas line sized correctly?
Is there a gas leak or low supply?

Fix:
Ensure the gas valve is open. If you suspect supply or sizing issues, call a licensed HVACR technician immediately—never attempt to repair a gas line on your own.

5. Clean the Air Intake Filter

A clogged air intake filter restricts airflow and triggers combustion errors.

Fix:
Remove the intake filter, rinse it with water, let it dry, and reinstall it.

6. Examine the Venting System

Improper or blocked venting causes overheating, shutdowns, or no hot water.

Look for:

Loose vent connections
Birds’ nests or debris blocking the vent
Frozen exhaust in winter
Incorrect venting materials

Fix any visible blockage. For venting errors or installation issues, professional repair is usually required.

7. Check the Electrical Supply

Electric tankless systems may stop working due to electrical faults.

Check:

Tripped breaker
Loose wiring
Faulty outlet
Burnt components

Reset the breaker or replace a faulty outlet. If wiring is damaged, call a technician—electric repairs can be dangerous.

8. Test the Temperature Setting

A simple fix: your hot water may not feel hot because the temperature is set too low.

Recommended setting:
120°F–125°F for most homes.

9. Reset the Tankless Water Heater

Sometimes glitches cause temporary malfunctions.

Fix:

Turn off the unit
Wait 30 seconds
Turn it back on

If the problem persists, continue troubleshooting or call Michigan HVACR for expert tankless water heater repair.

Tankless Water Heater Maintenance Tips

Preventing issues is easier than fixing them. Follow these tankless water heater maintenance practices:

Annual Descaling: Removes mineral buildup
Clean Air Filter Every 6–12 Months
Flush System Once per Year
Inspect Vents and Drain Lines
Test Pressure Relief Valve
Check Gas and Electrical Connections
Have Professional Maintenance Annually

Regular maintenance drastically reduces tankless water heater problems and prolongs lifespan.

When to Call a Professional

While many homeowners can perform basic tankless water heater troubleshooting, certain issues require a licensed HVAC technician—especially those involving:

Gas leaks
Electrical issues
Internal component failure
Repeated error codes
Heat exchanger problems
Persistent no hot water situations

Michigan HVACR specializes in tankless water heater repair, installation, and maintenance throughout the state. If DIY steps don’t fix the problem, we are here to help.

FAQs

1. Why is my tankless water heater not heating water?

Common causes include mineral buildup, ignition failure, low water flow, or blocked vents. Start by checking error codes and confirming water flow.

2. How often should I flush my tankless water heater?

At least once a year. In hard-water areas like much of Michigan, every 6–9 months is recommended.

3. Can I fix tankless water heater error codes myself?

Some can be resolved with basic troubleshooting. Gas or electrical-related codes should always be handled by a professional.

4. Why does my tankless water heater make a loud noise?

Usually from mineral buildup inside the heat exchanger. Flushing the system should help.

5. Why do I get no hot water at all?

Possible reasons include lack of gas supply, tripped breakers, frozen pipes, or clogged filters.