Element resistance testing is the first diagnostic step on any Stiebel Eltron "no hot water" or "lukewarm" complaint. A 10-minute multimeter test identifies which element (if any) has failed before you order parts.
What you need
- Multimeter with Ω (resistance) function
- Phillips and flathead screwdrivers
- Voltage tester (verify power is OFF before touching anything)
- Phone camera (photograph wiring before disconnecting)
Procedure
- Power OFF at all breakers. Tempra Plus has 2-3 high-amperage breakers. ALL must be off
- Verify with voltage tester at the unit terminals — confirm no voltage present
- Open the unit per service manual
- Photograph wiring at the contactor before disconnecting
- Disconnect one element\'s leads at the contactor (isolate that element)
- Set multimeter to Ω — auto-range or 200Ω scale
- Touch probes to the element terminals
- Read resistance and compare to spec
- Repeat for each element (Tempra 24/29/36 Plus have 3 elements)
Expected values by Tempra Plus model
| Model | Element count | Wattage each | Healthy Ω | Acceptable range |
|---|---|---|---|---|
| Tempra 12 Plus | 2 | 7.2 kW | ~8 Ω | 7-10 Ω |
| Tempra 15 Plus | 2 | 7.2 kW | ~8 Ω | 7-10 Ω |
| Tempra 20 Plus | 2 | 9.6 kW | ~6 Ω | 5-7 Ω |
| Tempra 24 Plus | 3 | 8 kW | ~7.2 Ω | 6-9 Ω |
| Tempra 29 Plus | 3 | 9.6 kW | ~6 Ω | 5-7 Ω |
| Tempra 36 Plus | 3 | 12 kW | ~4.8 Ω | 4-6 Ω |
Interpreting results
- OL or infinite resistance: element failed open (burned out). Replace
- Near 0 Ω: element shorted internally. Replace
- Out of spec by more than 20%: element degraded. Will run hot, draw more current, eventually fail. Plan replacement
- Within spec: element healthy. Issue is elsewhere (contactor, control board, voltage)
Element-to-ground short test
Critical secondary test. With multimeter still on Ω:
- Touch one probe to an element terminal
- Touch the other probe to the unit housing/ground
- Should read OL (open)
- Continuity to ground = element shorted to sheath — replace immediately. Continuing to operate the unit can damage the contactor and trip breakers
What to do with results
| Test result | Action |
|---|---|
| All elements within spec, no ground short | Issue is not element. Check contactor, voltage, control board |
| One element failed | Replace that element. Output capacity will be reduced until replaced |
| Multiple elements failed | Investigate root cause — voltage spike, water damage, hard-water scaling |
| Ground short detected | Replace element immediately; verify breaker condition |
After replacement: re-test
After installing a new element:
- Re-test all elements (verify new element is in spec)
- Re-test element-to-ground (verify no ground short on new element)
- Verify contactor operation by listening for click on call for heat after restoring power and flow
Bottom line
Element ohm test is the cheapest, fastest diagnostic on any electric tankless. Always test before ordering parts. Element-to-ground short test catches dangerous conditions that simple resistance test misses.