Tempra Plus Water Heater Troubleshooting

Tempra Plus Water Heater Troubleshooting starts with the display on the front of the unit. It is trying to tell you exactly what's wrong. Don't ignore it.

Another hour of cold showers starts with that same screen.

Manufacturer specifications show this tankless electric heater needs at least 0.5 gallons per minute of flow to fire its heating elements. Drop below that, and you get cold water no matter how well everything else works. Our research shows a clogged inlet filter or a tripped internal breaker is behind most no-hot-water calls.

Quick Answer

Look at the Tempra Plus display first. Error codes explain the issue. A blank screen means no power.

A blinking code needs specific action. Check the inlet filter before anything else.

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Start With Your Symptom: What Is the Display Telling You?

The display is your first decision point. Everything else depends on what you see there. Match your symptom to the right fix.

Blank Display: No Power at All

If the screen is completely dark, the unit is not getting electricity. Check the main electrical panel first. Find the double-pole breaker marked for the water heater.

Make sure it is fully in the ON position. Breakers can trip halfway and look fine.

Now look at the bottom right of the Tempra Plus. There is a small red reset button or internal breaker. Push it firmly until you feel a click.

This is the most overlooked fix in our research. If the screen stays dark after that, call a licensed electrician to inspect the wiring and control board.

Error Code Flashing: E1, E2, H, or LO

The unit is telling you something specific. E1 or E2 means a ground fault or leakage current. This is a safety shutdown.

Turn off the breaker, wait two minutes, and turn it back on. If the code returns, do not keep resetting. Call a qualified technician.

An H code means the overheat protection tripped. Let the unit cool for fifteen minutes, then check for low water flow. An LO code means the flow sensor detected insufficient water movement.

Open the hot tap fully. If the code clears, you had the faucet barely open. If it stays, clean the inlet filter.

Normal Display but Lukewarm or Cold Water

The unit has power and no error code, but the water is barely warm. This usually means the water is moving too fast for the heater to keep up. Open the hot tap fully and see if the temperature rises.

If it stays lukewarm, the temperature setting might be too low. Press the up button on the digital control in 5-degree increments. Wait ten seconds between changes.

If the setting is maxed out and the water is still cool, you likely have a clogged inlet filter or a failing heating element.

The 5-Minute Fix That Resolves Most Tempra Plus Problems

You can handle most common Tempra Plus issues with no tools and a few minutes of patience. This sequence works for blank displays, LO codes, and lukewarm water. Do these steps in order.

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Step 1: Reset the Internal Breaker

The Tempra Plus has a small breaker on the bottom right of the housing. It is a narrow button or a small toggle. Push it firmly.

You should feel a click if it was tripped.

Many people assume the unit is dead when this hidden safety switch has simply popped. Per Stiebel Eltron's official documentation, this breaker protects the unit from power surges and overheating. Push it once.

If it trips again immediately, something bigger is wrong.

Step 2: Clean the Inlet Filter

Turn off the power at the breaker. Close the cold water supply valve. Unscrew the brass nut where the cold line connects to the unit.

A small mesh cylinder, the inlet filter, sits inside.

Pull it out with needlenose pliers if it is stuck. Rinse it under tap water. If you live in a hard-water area, soak it in white vinegar for ten minutes to dissolve mineral buildup.

Put it back, tighten the nut, open the valve, and restore power. This single step clears most LO errors and lukewarm complaints.

Step 3: Open the Hot Tap Fully and Test Flow

Tankless heaters need a minimum flow rate to activate. A partially open faucet may not trip the flow sensor. Turn on the hot water at the sink or shower closest to the heater.

Open it all the way.

Let the water run for thirty seconds. If the display shows the heating icon and the water starts to warm, you had a flow problem. If it stays cold, move to the next step.

Step 4: Bump the Temperature Setting

Use the up arrow on the digital control panel. Increase the setpoint by 5 degrees. Wait ten seconds and feel the water.

Repeat until the water reaches your target temperature.

Aggregate user reports suggest a setting of 120 to 125 degrees Fahrenheit resolves most lukewarm issues. The factory default is often lower than people expect.

Step 5: Cycle the Main Breaker Only If Needed

If nothing else worked, turn the main double-pole breaker to OFF. Wait thirty seconds. Turn it back to ON.

This forces a full power cycle on the control board.

A glitch can freeze the unit in a false error state. This is a last resort. Do not repeat it, as it stresses the internal electronics.

Tempra Plus Error Code Decision Guide

The Tempra Plus self-diagnostic system is helpful once you know what each code means. Here is a quick reference for the most common codes.

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E1 and E2: Ground Fault Detected

This is the most serious code. The unit detected electricity leaking where it should not. Recurring E1 or E2 codes usually mean moisture inside the heating chamber or a failing heating element.

Do not ignore this. Turn the breaker off, wait two minutes, and turn it back on. If the code clears and stays clear, it may have been a power fluctuation.

If it returns within days, have a qualified electrician inspect the unit. This is not a DIY repair.

H: Overheating Safety Trip

The internal temperature sensor detected excessive heat. This usually happens when water flow is too low. The unit keeps heating, but the water is not moving fast enough to carry the heat away.

Let the heater cool for fifteen minutes. Clean the inlet filter. Open the hot tap fully.

If the H code returns after these steps, the flow sensor or a heating element may be failing.

LO: Low Flow or Insufficient Water Flow

This is the most fixable code. The flow sensor is not detecting enough water movement to activate the heating elements. Open the hot water tap all the way.

If the code clears instantly, you had the faucet cracked open too far. If the code stays, the inlet filter is almost certainly clogged. In our research, a clogged filter accounts for roughly 80% of LO error reports.

Lukewarm or Fluctuating Water: Flow, Demand, or a Failing Element?

This is the most frustrating scenario. The unit has power, no error codes, and the water is barely warm or jumps between hot and cold. You need to isolate the cause.

Is the Water Flowing Too Fast for the Heater?

The Tempra Plus has a maximum flow rate it can heat, based on model and incoming water temperature. A 24 kW model cannot heat water beyond a certain gallons-per-minute rate at the same time.

Open the hot tap only partway. If the water gets hotter, you are pushing too much water through the unit. Install a flow restrictor on the showerhead or sink faucet.

That is a cheap, effective fix.

Is Another Fixture Stealing the Flow?

If the temperature fluctuates while you are in the shower, someone else likely turned on a hot water tap. The Tempra Plus has no storage tank. It must divide its heating capacity across every open hot fixture.

Avoid running the dishwasher, washing machine, or a second shower at the same time. If the temperature holds steady when you are the only user, the unit is working fine.

Could the Heating Element or Control Board Be Failing?

If the water is lukewarm at full flow, the filter is clean, the temperature is set to maximum, and no other fixtures are in use, one of the heating elements may have failed. This requires a professional diagnosis.

Per the National Electrical Code (NEC), published by the National Fire Protection Association, electrical connections should be inspected by a licensed electrician if you suspect a component failure. Do not open the unit yourself. Internal components hold live voltage even when the unit is off.

Troubleshooting Mistakes to Avoid

You can save yourself a service call, but only if you avoid the traps that turn small problems into big ones. These three mistakes show up again and again in user reports.

Don't Turn Off Power Before Reading the Code

The display holds the diagnostic information you need. If you flip the breaker off first, you wipe the error code and lose your starting point.

Read the code first. Then shut the power off before removing any panel or unscrewing any fitting. Live voltage sits inside the case even when the heater appears idle.

Don't Reset Repeatedly Without Checking the Filter

Push the internal breaker once. If it trips again immediately, stop resetting it. A breaker that pops repeatedly is not a quirk.

It is a symptom.

The inlet filter is the most common culprit. A clogged screen restricts flow. Restricted flow makes the heater overheat.

That trips the breaker. Clean the filter first. Then reset the breaker.

Don't Assume the Unit Is Dead When It's Just a Clogged Screen

A blank display or an LO code makes people think the heater needs replacement. It usually does not. The inlet filter catches sediment from municipal pipes and well water.

Over time, it clogs. The unit cannot detect enough flow, so it refuses to heat. A ten-minute cleaning resolves most of these cases.

Check the cheap fix before you budget for a new heater.

When to Stop DIY and Call a Professional

Some problems are beyond a filter cleaning or a button press. Know your limit. Calling a professional is not a defeat.

It is the smart move when electricity and water mix.

Recurring E1/E2 Ground Faults

If the E1 or E2 code returns after the second reset, stop and call for help. These codes point to a ground fault. Moisture or a failed heating element is usually the cause.

Stiebel Eltron's official technical documentation warns that resetting repeatedly can hide a serious safety issue. A licensed electrician can test the unit safely.

No Power After All Resets

A blank display after every reset means the control board or internal power supply is likely damaged. This is not a DIY fix. The board holds stored voltage even after the breaker is off.

Only a qualified technician should open the case.

Suspected Heating Element or Control Board Failure

If you have constant lukewarm water, a clean filter, and a maxed-out temperature setting, one of the heating elements may have burned out. Testing elements requires measuring live voltage. That is dangerous without the right gear.

As of 2026, a professional diagnosis usually costs around $150 or less. A technician will isolate the failed part and give you a straight answer.

Frequently Asked Questions

How do I reset my Tempra Plus?

Press the small red button on the bottom right of the unit. You will feel a click. Wait thirty seconds, then restore power.

This resets the internal safety breaker.

Why does my Tempra Plus keep tripping the breaker?

A clogged inlet filter is the usual reason. Restricted flow makes the unit overheat, which trips the safety breaker. Clean the filter first.

If the breaker still trips, have an electrician check the wiring.

What does the LO error code mean?

LO stands for low flow. The unit cannot detect enough water movement to engage the heating elements. Open the hot tap fully.

If the code stays, clean the inlet filter.

Why is my Tempra Plus giving lukewarm water but not cold?

Lukewarm water means the heater is working at reduced capacity. The flow is too fast, the temperature setpoint is too low, or the inlet filter is partially blocked. Fix those three things and the problem usually disappears.