Tankless Water Heater Not Heating Your Water? Columbia Homeowners’ Guide

Losing hot water is frustrating, especially when it happens without warning. If you’re a Columbia homeowner with a tankless water heater that isn’t heating your water, one minute everything may seem fine, and the next you’re standing at the sink with nothing but cold water. Tankless water heaters are popular across Columbia and the Midlands, but when they stop heating, it can be confusing to figure out why.

The good news is that most cases where a tankless water heater is not heating fall into a few common categories. Some issues are simple and safe to check on your own. Others need professional attention. This guide breaks down what’s usually going on and what to do next.

Why Tankless Water Heaters Sometimes Stop Heating Water

Tankless systems work differently than traditional water heaters. Instead of storing hot water, they heat it on demand. To do that, the unit relies on steady water flow, power or gas supply, and internal sensors working together.

When any of those pieces are off, you may end up with no hot water, lukewarm water, or hot water that cuts in and out. Most problems are diagnosable once you know where to look.

Common Reasons a Tankless Water Heater Is Not Working

Homeowners usually notice one of a few patterns when a tankless water heater is not producing hot water.

You may see:

• No hot water at any faucet
• Water that starts hot and turns lukewarm
• Hot water that cuts out during use
• The unit appears on but isn’t heating

Each of these points to a different type of issue.

Not Enough Water Flow to Activate the Unit

Tankless water heaters need a minimum flow rate to turn on. If water flow is too low, the unit won’t activate the heating elements.

This can happen when:

• Multiple fixtures are running at the same time
• Aerators or filters are clogged
• Flow-restricting fixtures reduce water movement

What this means: The unit may be working correctly, but it’s not sensing enough flow to heat the water.

Power or Gas Supply Problems

If your tankless water heater has no hot water at all, power or gas is one of the first things to check.

Common causes include:

• A tripped breaker
• A shut-off gas valve
• Temporary gas pressure issues

What this means: Without power or fuel, the unit can’t heat water, even if everything else is fine.

Error Codes or Safety Shutoffs

Tankless systems are designed to shut down when they detect a problem. Error codes are a way for the unit to tell you something isn’t right.

Error codes often relate to:

• Overheating protection
• Venting or airflow issues
• Ignition or sensor faults

What this means: The system is protecting itself. Resetting without understanding the cause can make the problem return.

Mineral Buildup or Scale Inside the System

Over time, minerals in the water can build up inside the heat exchanger. This is common in tankless systems that haven’t been flushed regularly.

Scale buildup can:

• Reduce heating efficiency
• Cause inconsistent water temperature
• Trigger error codes or shutdowns

What this means: The unit may still run, but it can’t transfer heat properly. When your tankless water heater is not heating, call a professional plumber in Columbia, SC at (803) 590-8908.

Ignition or Heating Component Failure

In gas units, ignition components can wear out. In electric systems, heating elements can fail.

Symptoms may include:

• The unit turns on but never heats
• Hot water works briefly, then stops
• Repeated error codes

What this means: Internal parts may need repair or replacement.

What You Can Safely Check Yourself

Before calling for service, there are a few things most homeowners can check safely.

You can:

• Confirm the unit has power or gas
• Look at the display for error codes
• Reset the unit if the manufacturer allows it
• Make sure water flow is not restricted

What not to do:

• Don’t open the unit
• Don’t bypass safety features
• Don’t repeatedly reset without understanding the issue

If these checks don’t restore hot water, it’s time to stop and get help from the experts at Meetze Plumbing.

Why the Water Temperature May Be Inconsistent

Some homeowners don’t lose hot water completely. Instead, the temperature fluctuates.

Common reasons include:

• Cold inlet water during winter months
• Multiple fixtures running at once
• Demand exceeding the unit’s capacity

What this means: The system may be undersized for current usage, or conditions have changed since installation.

When a Tankless Water Heater Needs Professional Repair or Replacement

You should call a plumber if:

• The unit repeatedly shuts down
• Error codes won’t clear
• There’s no heat after basic checks
• You see leaks or signs of internal damage

At that point, a professional plumber can determine whether repair makes sense or if it’s time to think about replacement. Age of the unit, frequency of issues, and overall condition all factor into that decision. This is also a good time to compare tankless vs tank water heaters, since each option offers different benefits when it comes to upfront cost, energy efficiency, and long-term performance.

If you’re also noticing other symptoms, such as a water heater making weird noises or performance that keeps getting worse, those can be signs of deeper problems. When it’s time to replace your water heater, call the team you can trust at Meetze Plumbing in Columbia, South Carolina.

Getting Your Hot Water Back

A tankless water heater not heating is stressful, but most issues are fixable. Many problems come down to flow, power, maintenance, or components that wear over time.

If your tankless water heater has no hot water and basic checks don’t help, it’s best to have it looked at before the issue causes more downtime.

If you need help, call Meetze Plumbing at (803) 590-8908 to schedule service. We help Columbia homeowners troubleshoot tankless water heaters and get hot water back safely.

FAQs

Why is my tankless water heater running but not heating?

This usually points to flow issues, scale buildup, or a failed heating component.

Can mineral buildup stop a tankless water heater from heating?

Yes. Scale can block heat transfer and cause the unit to shut down or heat poorly.

Is it safe to reset a tankless water heater?

Only if the manufacturer allows it. Repeated resets without fixing the cause can lead to more problems.

How long should a tankless water heater last?

With proper maintenance, tankless systems often last longer than traditional tanks, though lifespan depends on usage and water quality.