Stiebel Eltron Water Heater Error Codes

Common Symptoms

• Tempra LED display shows E1 — upper heating module overheated
• Tempra LED display shows E2 — lower heating module overheated
• Tempra LED display shows E3 — inlet water thermistor fault
• Tempra LED display shows E4 — outlet water thermistor fault
• Tempra LED display shows F1 — flow sensor fault
• Hot water flow rate is reduced but no error code appears (AFC behavior — normal)
• SHC/SH storage tank: no display, no hot water, ECO reset button needed

Most Likely Causes

1. 1

   E1 — Upper Heating Module Overheat (Thermal Cutout Trip)

   E1 indicates the upper heating module's thermal cutout has tripped due to overheating. Primary cause in hard water areas: mineral scale (calcium/magnesium) coating the module walls, reducing heat transfer and causing local overheating. Secondary causes: inadequate flow through the unit (inlet valve not fully open, clogged inlet filter, or flow below the minimum), or a failed thermostat sensor. The thermal cutout is a resettable safety device — press the red reset button on the Tempra unit. If E1 recurs, descale the unit with the Stiebel Eltron descale kit (part 234584) or CLR flush.

2. 2

   E2 — Lower Heating Module Overheat (Thermal Cutout Trip)

   E2 is identical in cause and remedy to E1 but relates to the lower heating module. Tempra 20, 24, and larger models have multiple heating modules; E1 and E2 can occur independently or together. Scale buildup in the lower module is the most common cause in areas with water hardness above 10 grains per gallon. Reset with the red reset button; if E2 recurs within a short operating period, descale the unit.

3. 3

   E3 — Inlet Water Thermistor Fault

   E3 indicates the inlet water temperature sensor (thermistor) is reading outside the expected range — either an open circuit (sensor wiring disconnected or sensor failed) or a reading that falls outside the plausible range. The Tempra uses the inlet thermistor to calculate the required temperature rise. A failed inlet thermistor causes the unit to shut down as a safety precaution. Check the thermistor wiring connections before ordering a replacement thermistor.

4. 4

   E4 — Outlet Water Thermistor Fault

   E4 indicates the outlet water temperature sensor (thermistor) has failed or its reading is outside the expected range. The outlet thermistor verifies that delivered water temperature matches the set point — a failed sensor prevents the unit from confirming delivery and triggers shutdown. As with E3, check wiring connections at the thermistor before replacement.

5. 5

   F1 — Flow Sensor Fault

   F1 indicates the flow sensor has either failed to detect flow when flow is expected, or is reading an implausible flow value. The flow sensor is a turbine-type sensor in the cold water inlet. Causes: mineral scale or sediment jamming the turbine wheel, a broken turbine, or a failed sensor wiring connection. Remove and inspect the flow sensor for debris; clean the turbine. If the turbine is damaged, replace the flow sensor assembly.

6. 6

   No Code — Advanced Flow Control (AFC) Reducing GPM

   Advanced Flow Control is not a fault — no error code is displayed. AFC activates when the Tempra's heating element cannot raise inlet water to the set temperature at the current demand. The unit reduces flow rate (GPM) automatically to deliver water at the set temperature rather than delivering lukewarm water. Users experience reduced water pressure at hot fixtures. There is no reset needed. To restore full flow: lower the temperature set point, reduce simultaneous fixture demand, or verify the breaker and wiring are correctly sized for the Tempra model.

7. 7

   SHC/SH Storage Tank — No Display, ECO Thermostat Reset Needed

   SHC/SH storage water heaters have no digital display and show no error codes. When the ECO (energy cutoff) high-limit thermostat trips, the tank produces no hot water but gives no indication other than cold water at the tap. Diagnosis: remove the access panel, fold back the insulation, and look for the red ECO reset button above the thermostat dial. Press it firmly. If the ECO trips again, the thermostat may be set above 140°F, the element has failed, or there is scale buildup on the element reducing heat transfer.

Quick DIY Checks

1. 1Step 1 — Read the Tempra display. The Tempra LED panel displays error codes directly. Note the exact code displayed (E1, E2, E3, E4, or F1). If the display shows a normal temperature reading but hot water flow is reduced, this is AFC — not an error code — go to Step 3. If the display is blank, go to Step 8 (no power / breaker check).
2. 2Step 2 — E1 or E2: red reset button procedure. Locate the red reset button on the front of the Tempra unit. On most Tempra models, it is a small red button behind a cover on the front panel or on the side panel — consult the unit's installation manual for the exact location on your specific model. Turn off the dedicated breaker. Wait 5 minutes for the module to cool. Turn the breaker back on. Press and release the red reset button. Open a hot tap and verify the E1/E2 code has cleared and hot water flows. If E1/E2 returns within 5–10 minutes of operation, proceed to the descale procedure (Step 4).
3. 3Step 3 — AFC behavior (no code, reduced flow): confirm this is AFC and not a fault. Check that the Tempra display shows the normal set temperature (no error code). Measure the cold inlet water temperature with a thermometer (or check your local utility's reported groundwater temperature for the season). Calculate: if your set temperature is 120°F and cold inlet is 45°F, the required temperature rise is 75°F. At 75°F rise, the Tempra 20 (19.2 kW) delivers approximately 0.8 GPM maximum. If your demand exceeds this (e.g., simultaneous shower + kitchen sink), AFC will reduce flow. Solution: lower the set temperature to reduce required temperature rise, reduce simultaneous fixtures, or upgrade to a Tempra 24 Plus or Tempra 36 Plus with higher kW capacity.

1. 4Step 4 — Descale procedure for E1/E2 (after reset, if code recurs). Turn off the dedicated Tempra breaker. Close the cold water supply valve to the unit and open a hot tap to depressurize. The Stiebel Eltron descale kit (part 234584) includes a pump adapter fitting and hose. Alternatively, use a submersible pump, two garden hoses, and a 5-gallon bucket with 4 gallons of undiluted white vinegar or CLR. Connect the inlet hose from the pump bucket to the cold inlet, and the outlet hose from the hot outlet back to the bucket. Run the pump to circulate the descaling solution through the unit for 60 minutes. After descaling, flush with clean water for 15 minutes. Restore cold water supply and breaker. Verify E1/E2 does not return. Install a scale inhibitor filter on the cold supply if water hardness exceeds 10 GPG.
2. 5Step 5 — E3 or E4 (thermistor fault): turn off the Tempra breaker. Remove the front panel. Locate the inlet thermistor (E3 — on the cold water inlet side) or outlet thermistor (E4 — on the hot water outlet side). Inspect the thermistor wiring connector for corrosion, moisture, or a loose connection — reseat the connector firmly. Restore power and check if the code clears. If the code persists, test the thermistor resistance with a multimeter: a typical NTC thermistor at room temperature should read 10–15 kΩ (consult the Tempra service manual for the exact spec for your model). An open circuit or zero resistance indicates thermistor failure — contact Stiebel Eltron at 1-800-STIEBEL to order a replacement thermistor.
3. 6Step 6 — F1 (flow sensor fault): turn off the Tempra breaker and close the cold water supply. Remove the front panel. Locate the flow sensor on the cold water inlet — it is a turbine-type sensor with a wiring harness. Disconnect the wiring harness and remove the sensor from its port (using an adjustable wrench or socket). Inspect the turbine wheel inside the sensor for scale, sediment, or debris — clean with white vinegar if scaled. Verify the turbine spins freely. Reinstall the sensor, reconnect the wiring harness, restore cold water supply and breaker. If F1 persists after cleaning, the flow sensor turbine is damaged — contact Stiebel Eltron for a replacement flow sensor.
4. 7Step 7 — SHC/SH storage tank (no display — ECO reset procedure): turn off the dedicated SHC/SH breaker. Remove both access panels on the side of the tank (upper and lower) and fold back the insulation pads. Locate the red ECO reset button above the thermostat dial on each panel — there may be both an upper and lower thermostat assembly. Press and release the red ECO reset button firmly on each assembly (you should feel or hear a click). Also verify the thermostat dial is set to the correct temperature (140°F maximum for safety). Reinstall insulation and panels, restore the breaker, and allow 45–60 minutes for the tank to fully reheat before testing.
5. 8Step 8 — Blank display / no power: go to the electrical panel and locate the dedicated Tempra breaker (double-pole). Verify the breaker amperage matches the Tempra model spec (Tempra 12 = 60A; Tempra 20 = 100A; Tempra 24 Plus = 100A; Tempra 29 Plus = 125A; Tempra 36 Plus = 150A). A tripped breaker is in the middle position — push fully to OFF then back to ON. If the breaker trips again immediately under load, do not reset repeatedly — call an electrician. A breaker that trips on reset indicates a short circuit in the heating module or wiring.

Repair vs Replace

Recommended Tools & Parts

• Stiebel Eltron Descale Kit (Part 234584)

  Stiebel Eltron's descale kit for Tempra electric tankless water heaters, designed to clear mineral scale that causes E1/E2 overheat faults. Includes adapter fittings for the Tempra's inlet and outlet.

  $40–$60

  Buy on Amazon →

• CLR Calcium Lime Rust Remover

  Alternative to the Stiebel Eltron descale kit for clearing mineral scale causing E1/E2 codes. Use undiluted. Flush thoroughly with water after use. Effective for moderate hard water scale on Tempra heating modules.

  $10–$20

  Buy on Amazon →

• Digital Multimeter

  Required for testing thermistor resistance (E3/E4 diagnosis) and verifying 240V power is off before internal sensor work.

  $15–$35

  Buy on Amazon →

• Non-Contact Voltage Tester

  Mandatory safety tool for confirming the 240V Tempra circuit is dead before removing panels or touching internal wiring, thermistors, or the flow sensor.

  $15–$30

  Buy on Amazon →

Links are Amazon affiliate links (tag: fixitfastai-20). Prices are estimates.

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