Fluctuating Water Temperatures

The most common complaint we hear is water that goes from hot to lukewarm or even cold during a single use. This is often called a cold water sandwich, where the unit struggles to maintain a steady flame while water flows through it. This is usually caused by a malfunctioning flow sensor or a partially clogged heat exchanger that cannot keep up with the demand.

In areas with hard water like ours, mineral buildup can insulate the heat exchanger. This prevents the unit from consistently heating the water as it passes through the system. When the sensors detect the water is not reaching the right temperature, they might throttle the unit down or cause it to cycle on and off rapidly.

The Impact of Inconsistent Heat

This does not just make for an uncomfortable shower experience. It also indicates the unit is struggling and using much more energy than it should. The constant cycling puts unnecessary stress on the ignition system and the gas valves, which can shorten the lifespan of your heater.

Our technicians will perform a diagnostic check on all the internal sensors to see where the communication is breaking down. We can conduct a professional descaling service to flush out the heat exchanger and restore its original heating efficiency. This typically smooths out the temperature and makes your hot water reliable again.

Low Hot Water Pressure

If you notice a significant drop in hot water pressure at all your faucets, the problem is likely inside the tankless unit itself. This is different from a plumbing leak, which usually only affects one area of the house. When the whole house loses hot water pressure but the cold water stays strong, the unit is the bottleneck.

Scale and sediment from the local water supply can build up inside the narrow copper pipes of the unit. These deposits also gather at the inlet and outlet valves, creating a restriction that slows the flow of water. Over time, this blockage can become severe enough to reduce your hot water to a tiny trickle.

Restoring Your Water Flow

This buildup puts immense strain on your home’s pipes and the internal pump of the water heater if it has one. We use specialized pumps and cleaning solutions to safely dissolve these mineral deposits without damaging the sensitive internal components. We do not use harsh chemicals that could corrode the copper; we use solutions designed specifically for tankless systems.

Once the lines are cleared, you will notice an immediate difference in how fast your tubs fill and how well your high-flow showerheads perform. Keeping these passages clear is the best way to ensure your system does not overheat. A clear path for water means the heat exchanger can transfer energy efficiently without getting too hot.

Strange Noises Like Knocking or Gurgling

Tankless water heaters should be relatively quiet during operation, usually making just a slight whirring sound from the fan. If you start hearing loud humming, clanking, or gurgling sounds, it points to a serious issue with sediment or boiling water inside the heat exchanger. This is a critical warning sign that the unit is not operating within its safe parameters.

The clanking or “kettling” sound is caused by water getting trapped behind layers of scale and boiling instantly. This creates small steam bubbles that pop and create pressure spikes inside the heat exchanger. If this continues, the constant vibration and pressure can cause the metal to fatigue and eventually crack.

Preventing Heat Exchanger Damage

A cracked heat exchanger is often the end of the road for a tankless unit because the part is so expensive to replace. A technician will immediately inspect the unit to see if the noise is coming from the burner or the water path. In most cases, catching this early and performing a professional descaling service can resolve the issue before permanent damage occurs.

We also check the internal fan and motor during these calls. Sometimes debris or a failing bearing can cause a loud humming noise that resonates through your walls. Identifying the specific type of noise helps us pinpoint whether we are looking at a plumbing issue or a mechanical failure.

The Unit Shuts Off or Displays an Error Code

Modern tankless heaters have built-in diagnostics that will shut the system down and display a numeric error code if a problem is detected. These codes are there to protect you and the machine from dangerous conditions like overheating or exhaust gas backup. If your unit is showing a code, it has sensed something that could cause a breakdown or a safety hazard.

These codes can point to a range of issues, from simple vent blockages to complex ignition failures. In our wooded areas, it is common for small animals or debris to find their way into the exterior vent terminals. While a simple reset might get the hot water back for an hour, a recurring error code signals an underlying problem that needs professional diagnosis.

Interpreting Diagnostic Codes

Our technicians are trained to interpret the diagnostic codes for all major tankless brands. We do not just look at the code and swap a part; we find out why the part failed in the first place. Whether it is a dirty flame sensor or a faulty circuit board, we find the root cause to ensure the repair lasts.

Safety is the main reason these codes exist. For example, if the unit detects that the exhaust is not venting properly, it will shut down to prevent carbon monoxide from entering your home. We take these codes seriously and ensure every safety limit is tested before we leave your house.

What’s Causing My Tankless Water Heater Problems?

Mineral Buildup and Scale

The number one cause of tankless issues in Tennessee is scale from hard water. Our local water contains minerals like calcium and magnesium that solidify when they are heated. These deposits coat the inside of the heat exchanger, acting like a thick layer of insulation between the burner and the water.

Your unit is forced to work much harder and fire its burners longer to heat the water through that layer of scale. This drives up your utility bills and causes excessive wear and tear on the burner assembly. The fix involves a professional descaling, or “flushing,” of the system to remove every bit of buildup.

How Professional Flushing Works

Our technicians circulate a specialized, non-toxic solution through the unit for about an hour. This solution reacts with the calcium to dissolve it back into the liquid so it can be rinsed away. We recommend this service annually for most homes in the area to prevent major mechanical failures.

If you wait too long between flushes, the scale can become so thick that the solution cannot penetrate it. At that point, the heat exchanger may be permanently restricted. Regular maintenance is the only way to protect the high investment you made in your tankless technology.

Ignition or Flame Failure

If you can hear the unit click several times but it fails to produce hot water, you likely have an ignition problem. This can be caused by a dirty flame sensor that cannot “see” the fire, or a clogged gas orifice that isn’t letting enough fuel through. Over time, carbon deposits can build up on the igniter, preventing it from creating a strong enough spark.

Gas pressure issues can also prevent the unit from staying lit. If your gas regulator is failing or the line is undersized for the unit’s high demand, the flame will flicker out as soon as it starts. This is a common issue in older homes that were retrofitted with tankless units without upgrading the gas infrastructure.

Solving Electronic and Gas Issues

Our technicians will safely inspect the entire ignition sequence, from the gas valve to the control board. We check the voltage at the igniter and the microamps at the flame sensor to ensure everything is within factory specs. Sometimes a simple cleaning of the sensor is all it takes to get you back in business.

If the control board is the problem, we can diagnose which circuit has failed. Modern boards are sensitive to power surges and humidity, which are both common in our climate. We ensure your unit is properly grounded and protected to prevent these electronic failures from happening again.

Blocked Venting or Air Intake

Your tankless unit needs a clear path for air intake and exhaust to operate safely. These units move a lot of air because they burn gas at a very high rate to heat water instantly. Blockages in the pipes prevent proper combustion and cause the unit to shut down to prevent damage.

Debris, nesting birds, or even heavy spider webs can obstruct the vent terminals on the outside of your home. If the unit cannot pull in enough fresh air, the flame will be “lazy” and produce soot, which further clogs the heat exchanger. This creates a cycle of poor performance that eventually leads to a total lockout.

Ensuring Proper Ventilation

We thoroughly inspect the entire venting system from the unit all the way to where it exits your home. We check for proper slope in the pipes to ensure condensation does not back up into the heater. In Sparta, we often find that local environmental factors like high humidity can cause moisture to trap debris in the screens.

We make sure your venting meets all local safety codes. Improper venting is not just a performance issue; it can lead to dangerous exhaust gases staying inside your utility room or crawlspace. Our team ensures the seals are tight and the air path is completely clear.

What to Expect When Flatt’s Heating and Cooling Visits Your Home

When you call Flatt’s Heating and Cooling for service, we send a qualified technician who understands the specific needs of tankless technology. We do not just show up and start changing parts. First, the technician will listen to your description of the problem and look at any error codes the unit has stored in its memory.

Next, they will perform a multi-point inspection of the entire system. This includes checking the water inlet filter, assessing the condition of the heat exchanger, and testing the gas pressure. We also look at the electrical connections to ensure the unit is receiving steady power without interference.

Before any work begins, the technician will explain exactly what they found and what the repair options are. We believe in being transparent about what is necessary to get your hot water back and what can wait. Once you approve the work, we proceed with the service, whether it’s a descaling flush or a mechanical repair. Finally, we test the unit through several cycles to ensure the water temperature is stable and the unit is operating quietly.

Why You Shouldn’t Postpone Tankless Water Heater Service

Ignoring the warning signs from your tankless unit is a costly mistake that usually leads to a much larger bill later. What starts as a minor issue, like slight scale buildup, can quickly turn into a permanent failure of the heat exchanger. Since the heat exchanger is the most expensive part of the system, protecting it should be your top priority.

A struggling unit also consumes significantly more gas or electricity to do its job. The money you think you’re saving by delaying a service call is often being spent on higher utility bills month after month. You are essentially paying for the repair through your energy company without actually getting the benefit of a fixed machine.

Problems like poor combustion or blocked exhaust vents are serious safety hazards. These issues can lead to carbon monoxide buildup or fire risks if the unit is allowed to continue running in a degraded state. A scheduled service call to fix a small problem is far less expensive and disruptive than an emergency situation where you have no hot water and a potential safety risk in your home.