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Troubleshooting Tankless Water Heater Not Heating

Home | Blog | Published on September 26th, 2025

Tankless water heaters offer energy-efficient, on-demand hot water—but when they stop working, the impact is immediate. Whether you’re dealing with lukewarm water or none at all, it’s important to understand the common causes and when to call in the professionals. Real HVAC Services is here to help homeowners and businesses in Salisbury, MD quickly restore comfort with expert tankless water heater service.

HVAC technician testing electrical components on tankless water heater in Salisbury, MD

Common Reasons Your Tankless Water Heater Isn’t Heating

Power or Gas Supply Issues

If your tankless water heater isn’t turning on at all, the problem could stem from a tripped circuit breaker, blown fuse, or a disrupted gas supply. These types of issues can involve complex electrical or gas line concerns, so it’s always safest to have a licensed technician handle the inspection and any necessary repairs.

Mineral Buildup

Over time, hard water minerals like calcium and magnesium can accumulate inside the heat exchanger, restricting water flow and reducing the unit’s ability to heat properly. This buildup is a common reason for lukewarm or fluctuating water temperatures. Regular professional descaling is key to maintaining peak performance.

Cold Water Sandwich Effect

If you’re experiencing alternating hot and cold water bursts, you may be dealing with what’s known as the “cold water sandwich” effect. This occurs when residual hot water in the pipes is followed by a brief blast of cold water before the heater warms up again. Though not a mechanical issue, it can often be minimized with adjusted usage patterns or plumbing modifications.

Blocked Air or Exhaust Vents

Tankless systems require clear air intake and exhaust paths to function safely and efficiently. If vents become blocked by debris, animals, or snow, the system may shut down as a safety precaution. Because venting is connected to combustion, only trained professionals should inspect and resolve these issues.

System Overload

Tankless water heaters have a maximum capacity. If too many fixtures are drawing hot water simultaneously, the unit can become overloaded, leading to inconsistent temperatures or temporary shutdowns. A Real HVAC Services technician can help you evaluate whether usage adjustments or a higher-capacity system would better suit your needs.

Ignition or Flame Failure

When your unit clicks but doesn’t ignite, the problem could be related to low gas pressure, dirty ignition components, or a failing igniter. These issues can prevent the burner from firing and should be addressed by a professional with the proper diagnostic tools and training.

What You Can Safely Check

  • Confirm power is on and breakers are not tripped
  • Check for water supply to the unit
  • Try reducing simultaneous hot water use
  • If accessible, clean or replace the unit’s homeowner-friendly filter per the manual

If these steps don’t fix the issue, or if you suspect a gas, ignition, or venting problem, it’s time to call Real HVAC Services for expert assistance.

Why Choose Real HVAC Services?

At Real HVAC Services, we offer professional tankless water heater repair and maintenance for homeowners and businesses across Salisbury, MD and nearby areas. Our certified technicians are trained to diagnose and repair ignition systems and burner components, perform descaling and flushing services, clear and correct venting issues, conduct comprehensive system inspections and tune-ups, and recommend upgrades or replacements when needed.

We treat your home or business like it’s our own—with prompt, respectful service and a commitment to doing the job right.

Don’t let cold water ruin your day. Contact Real HVAC Services now for fast, reliable tankless water heater repair in Salisbury, MD.

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