If your Stiebel Eltron Tempra Plus water heater is not making hot water, the problem usually falls into one of four buckets: no power, not enough flow to activate the heater, water demand that exceeds the model’s heating capacity, or an internal fault such as scale buildup, a tripped thermal cutout, sensor failure, or flow sensor issue. The fastest way to troubleshoot is not to start replacing parts. Start with the model number, breaker status, actual gallons per minute at the hot fixture, and the display or error state.
On our job sites, we treat a Tempra Plus as both a plumbing appliance and a major electrical load. That matters. These are hard-wired, whole-house electric tankless heaters. They do not need gas combustion venting, but they can require multiple 240 V circuits, large copper conductors, and enough panel capacity to support 12 kW to 36 kW of demand. A Tempra 24 Plus can be a good fit in the right house, but it will disappoint if it is asked to serve too many fixtures at once in cold-water conditions.
This guide walks through the same sequence we use in the field: safe homeowner checks first, then flow and temperature diagnostics, then model-specific electrical and plumbing issues, then error codes, maintenance, costs, permits, and the line where a licensed electrician or plumber should take over.
Start With These Three Checks Before Opening Anything
Before anyone removes the cover, resets internal safety devices, or tests live voltage, gather three facts. They solve a surprising number of service calls.
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1. Confirm the exact Tempra Plus model
Look for the model number on the unit label: Tempra 12 Plus, 15 Plus, 20 Plus, 24 Plus, 29 Plus, or 36 Plus. The model tells you the electrical load, minimum activation flow, and realistic hot-water capacity. The current Tempra line ranges from 12 kW to 36 kW at 240 V.
The larger units are not just slightly bigger appliances. They can require multiple double-pole breakers and substantial service capacity. Manufacturer-recommended minimum main service is typically 100 A for Tempra 12 and 15, 125 A for Tempra 20, 150 A for Tempra 24, 200 A for Tempra 29, and 300 A for Tempra 36, depending on the total load in the home.
#1 Best Overall
- On demand a continuous and unlimited supply of hot water
- Sleek design saves space and no venting required, It also features two different temperature memory presets, making it easy to adjust for personalized needs.
- Requires hard-wired 240 or 208-volt electric service, with a maximum draw of 28,800 watts at 240 volts or 21,600 watts at 208 volts
- Requires 3 separate dedicated 40 amp breakers with 8 gauge copper wiring, and a minimum of 200 amp total service to the residence
2. Measure hot-side flow at the fixture
Do not guess by feel. Use a bucket and a timer. Run the hot side only into a 1-gallon or 5-gallon bucket and calculate gallons per minute. For example, if a shower fills a 1-gallon bucket in 24 seconds, that fixture is flowing 2.5 gpm.
Activation flow matters. Tempra 12 activates at about 0.37 gpm. Tempra 15, 20, and 24 activate at about 0.50 gpm. Tempra 29 and 36 activate at about 0.77 gpm. If an ultra-low-flow lavatory faucet, clogged aerator, partially blocked shower head, or fouled inlet screen keeps flow below that threshold, the heater may not fire even though the unit is not actually failed.
3. Check the display, power light, and error code
Note whether the display is on, whether the power light blinks, and whether an error code appears. If the power light blinks or the outlet temperature drops during high demand, reduce fixture flow and retest. On a Tempra Plus, reduced flow can be normal behavior. The Plus models use Advanced Flow Control, which intentionally throttles flow when demand exceeds heating capacity so the outlet temperature does not crash.
No Hot Water: The Practical Diagnostic Sequence
When a homeowner says, “We have no hot water,” we separate that into two cases: the unit is not turning on at all, or the unit turns on but cannot heat the water enough. The fix depends on which one you have.
Check the breakers, but do not stop there
Tempra Plus units are fed by dedicated 240 V circuits. Some models use more than one double-pole breaker. A partially tripped breaker can be easy to miss because the handle may sit between ON and OFF. Turn the affected breaker fully OFF, then back ON, if you can do so safely and your panel is properly labeled.
If the breaker trips again, stop. Repeated breaker resets are not troubleshooting. They are a warning sign. Possible causes include a wiring fault, failed component, incorrect breaker or conductor sizing, moisture intrusion, or internal overheating condition. That is electrician territory.
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Manufacturer-listed causes for no hot water include insufficient flow, clogged unit filter screen, clogged faucet aerator or shower head, a clogged or non-spinning flow sensor, and reversed hot/cold plumbing. That is why we check both ends of the system. A blocked shower head can mimic a heater failure just as convincingly as a dirty inlet screen.
Remove and clean faucet aerators and shower head screens first. These are homeowner-safe tasks. If flow improves and the heater begins working, the heater was not the root cause. If multiple fixtures have low hot-side flow, the inlet filter, service valves, plumbing restriction, or flow sensor may need professional service.
Verify plumbing orientation
Tempra units require cold water into the right-side connection and hot water out from the left-side connection. Connections are 3/4 in. NPT. Reversed plumbing can cause no heat, erratic heat, or poor operation that looks like an electrical problem.
This is especially worth checking after a remodel, relocation, or replacement. We have seen beautiful mechanical rooms where the problem was simply crossed piping. Do not assume it is correct because the unit is new.
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Water Is Lukewarm: Capacity, Flow, Voltage, or Scale
Lukewarm water is the most common Tempra Plus complaint, and it is often not a defective heater. Electric tankless performance depends on temperature rise: how many degrees the heater must raise incoming water at a given flow rate.
A useful benchmark: a 24 kW unit at 240 V can raise roughly 3.0 gpm by about 54 F. If incoming water is 50 F and you want 104 F shower water, that is a 54 F rise. One 2.0 to 2.5 gpm shower may work well. Add a second shower, a tub filler, or a washing machine, and the heater may hit its limit.
Rank #2
- CONTINOUS FLOW – Hot showers will never be interrupted again. Enjoy continuous, on-demand hot water with an unlimited supply, when you want it without wasting any energy when not needed
- SPACE & ENERGY SAVER – Its small, sleek white design saves space yet still provides endless hot water for your whole house, and no venting is required. Eco friendly unit saves energy with auto-modulation
- SILENT OPERATION – One electronic switch will activate the hot water heater and it’s noise free while in use. Digital temperature display is easy to read, while the interior solid copper heating system does all the power work
- TEMPRA 24 TREND – This specific model is 24kW, 240V, requires a min recommended electric service of 150 A, and offers an output water temperature of 68° to 140°F. Check our guides below to compare features of our various Trend and Plus models, each available in different kW levels
- WARRANTIES INCLUDED – Stiebel Eltron’s top-rated electric tankless water heaters perform with the highest standards for comfort and reliability. Our 7-Year Leakage and 3-Year Parts Warranties are included with purchase
In colder regions, incoming winter water can be much lower than summer water. A system that feels excellent in September can feel undersized in January. That is not a seasonal mystery; it is math.
| Symptom | Likely Cause | First Check | Who Should Handle It |
|---|---|---|---|
| No display or no heat anywhere | Breaker off, lost leg of power, wiring issue | Check all dedicated double-pole breakers | Homeowner for breaker check; electrician for testing |
| Hot water starts then turns lukewarm | Demand exceeds capacity or voltage drops under load | Measure gpm and compare to model capacity | Plumber/electrician if persistent |
| One fixture has poor heat | Clogged aerator, shower head, or fixture mixing issue | Clean aerator and compare another fixture | Homeowner or plumber |
| Flow drops when multiple fixtures run | Advanced Flow Control is limiting flow to preserve temperature | Run one fixture at a time, then add demand | Usually normal; plumber if sizing is wrong |
| Error 2 or Error 3 | Temperature sensor fault or cable issue | Record code and call technical support | Licensed pro |
| Heat gets worse over months | Scale on elements or clogged filter | Review descaling history and water hardness | Plumber for flush/service |
Reduce flow and retest
If the water gets hotter when you reduce the shower flow, the heater is probably working but overloaded. That points to sizing, fixture flow, incoming water temperature, or electrical supply. It does not automatically mean the control board or heating elements are bad.
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Voltage should be checked while the heater is actually running, not only at rest. Long conductor runs, undersized wiring, loose terminations, or panel issues can create voltage drop. Low supply voltage is a manufacturer-listed cause of water not hot enough.
This is not a homeowner test. A Tempra Plus contains high-voltage circuits, and larger models can draw serious current. Have a licensed electrician verify voltage, breaker sizing, conductor sizing, terminations, and load calculations.
Look for scale buildup
Scale on heating elements reduces heat transfer and can contribute to overheating or thermal cutout problems. Hard-water homes may need descaling every 6 to 12 months. If the original installation omitted isolation valves, flushing becomes more labor-intensive because the plumber may need to modify the piping before maintenance can be done cleanly.
Understanding Advanced Flow Control on Tempra Plus Models
The “Plus” in Tempra Plus matters. Stiebel Eltron’s Advanced Flow Control is designed to reduce water flow when demand exceeds the heater’s capacity. The goal is to maintain set temperature instead of allowing a sudden cold-water drop.
That means a flow reduction is not always a malfunction. If two showers, a dishwasher, and a lavatory faucet are running at the same time, the unit may throttle flow. From the user’s perspective, it can feel like the shower pressure dropped. From the heater’s perspective, it is doing exactly what it was designed to do.
The proper test is simple: run one hot fixture at a measured flow rate and record inlet temperature, outlet temperature, and setpoint. Then add fixtures one at a time. If the unit performs normally at one fixture but reduces flow at high demand, the issue is likely capacity, not a broken heater.
Error Codes 2 and 3: What They Mean
Tempra Plus error reporting includes Error 2 for inlet temperature sensor failure and Error 3 for outlet temperature sensor failure. Error 3 may involve an outlet sensor cable connection or require technical support.
When an error code is present, write it down before cycling power. Also record the model, serial number, set temperature, breaker configuration, measured flow, inlet temperature, and outlet temperature. Stiebel Eltron publishes US technical support at 800-582-8423. Calling support before opening the unit can save time, especially when a sensor or canister issue is suspected.
The unit has no average-user-serviceable internal parts. Manufacturer guidance is clear that malfunctions should be handled by a licensed plumber or electrician. Removing the cover, testing voltage, resetting internal thermal cutouts, replacing sensors, and working on wiring are professional tasks.
Can You Reset a Tempra Plus Yourself?
You can reset external breakers if it is safe to access your electrical panel and the breakers are labeled. That is where homeowner reset work should stop.
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- Reduces flow rate to maintain output temperature
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Internal thermal cutout resets are different. The manual warns not to reset the thermal cutout unless all breakers feeding the unit are completely off. On larger models, that may mean multiple double-pole breakers. If a thermal cutout tripped, the heater overheated or detected a safety condition. Resetting it repeatedly without finding the cause can damage equipment and create a safety hazard.
Common reasons a thermal cutout may trip include low flow, scale buildup, clogged filter screen, failed component, wiring problem, or incorrect installation. A licensed pro should determine why it tripped before putting the heater back into regular service.
Maintenance: Filters, Aerators, Descaling, and Water Quality
Tankless electric heaters are compact, but they are not maintenance-free. Water quality directly affects service life and may affect warranty coverage. Hard water is the main enemy because minerals can accumulate on heating elements and inside the water path.
Homeowner-safe maintenance
Clean faucet aerators and shower heads when flow drops or temperature becomes inconsistent. Check that hot-side valves are fully open. Keep the area around the heater accessible. Note any change that happened before the problem started, such as a new low-flow fixture, bathroom remodel, plumbing repair, or electrical panel work.
Professional maintenance
A plumber can clean the unit filter screen, verify flow through the heater, service isolation valves, flush/descale the unit, and check for reversed plumbing or restrictions. In hard-water homes, a 6 to 12 month descaling interval is a practical starting point. Homes with very hard water may need treatment equipment to protect the heater and other fixtures.
After descaling, we like to document flow rate, inlet temperature, outlet temperature, setpoint, and any error history. Those numbers make future troubleshooting much faster.
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Costs vary because a Tempra Plus problem can be as simple as a clogged aerator or as involved as electrical service upgrades. For basic, favorable-site professional installation, the May 2026 Homewyse national benchmark for a tankless electric water heater is about $1,642 to $1,925 per heater. That excludes permits, major electrical or plumbing modifications, hazardous-material work, and general contractor markup.
In the real market, installed tankless electric projects commonly land around $2,400 to $5,000 or more when panel capacity, new circuits, relocation, removal, difficult access, or high-labor markets are involved. Unit-only retail pricing for common Tempra Plus models such as the Tempra 24 Plus and Tempra 29 Plus is often in the mid-$600s to low-$700s range, varying by model, retailer, and location.
| Work Item | Typical 2026 Cost Pattern | What Drives the Price |
|---|---|---|
| Diagnostic service call | Trip charge or first-hour minimum | Local labor rate, plumber vs electrician, access, time on site |
| Aerator or shower head cleaning | Low cost if DIY | Fixture condition, mineral buildup, replacement parts |
| Professional descaling | Moderate service cost | Isolation valves, access, water hardness, flush time |
| Flow sensor, sensor cable, or control diagnosis | Variable repair cost | Error code, part availability, warranty status, labor |
| Breaker, wire, or voltage correction | Can be significant | Number of 240 V circuits, conductor size, panel capacity, run length |
| Full replacement | About $1,642-$1,925 basic benchmark; often $2,400-$5,000+ with modifications | Model size, electrical work, plumbing changes, permits, inspection |
The biggest variance driver is electrical infrastructure. A Tempra 36 Plus is not a like-for-like swap in a house with limited service capacity. Before replacing a unit, verify the home can support the model under the local electrical code and actual panel load.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Permits and Code: Do Not Skip the Local AHJ
Water heater replacement rules are local. The authority having jurisdiction, or AHJ, controls whether a permit is required, what drawings are needed, and whether inspection is required. Tankless electric units can trigger both plumbing and electrical review because they involve water piping plus high-amperage circuits.
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Permit fees vary widely. Examples from 2026 references include about $103 for a water-heater replacement permit in Palatine, Illinois, $180 in Bend, Oregon, and a reported $131 minimum water-heater replacement permit in Houston. Those examples are not universal prices. Your city or county may be lower, higher, or may require different submittals.
Permit review is not just paperwork. Inspectors may look at breaker sizing, wire sizing, disconnect requirements, working clearances, bonding, pressure range, pipe materials, and whether the unit is installed according to the manufacturer’s instructions. For Tempra units, remember the normal operating pressure range is 30 to 150 psi, water connections are 3/4 in. NPT, and the maximum outlet temperature is up to 140 F depending on flow rate.
When to DIY vs When to Hire a Pro
A smart homeowner can do useful troubleshooting without taking unsafe risks. The dividing line is simple: anything outside the cover and away from live electrical testing may be reasonable; anything inside the unit or involving wiring belongs to a licensed professional.
Reasonable homeowner checks
Confirm the model number. Check the display and write down error codes. Verify all dedicated breakers are on. Clean faucet aerators and shower heads. Measure fixture flow with a bucket and timer. Reduce shower flow and see whether temperature improves. Check whether the problem started after new fixtures, plumbing work, or electrical work.
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- Reduces flow rate to maintain output temperature
- Backlit multifunction display
- Output temperature presets
- Energy savings calculator
Call a licensed plumber
Hire a plumber for filter screen cleaning, descaling, isolation valve installation, reversed hot/cold piping, flow sensor service, water pressure concerns, leaks, or persistent low hot-side flow. Also call a plumber if hard water is recurring and the home may need treatment.
Call a licensed electrician
Hire an electrician for voltage testing, breaker trips, conductor sizing, panel load analysis, loose terminations, new circuits, service upgrades, or any sign of heat damage at the panel or heater. Measure voltage under load, not only at rest, because voltage drop can cause “not hot enough” complaints even when the unit appears powered.
Field Checklist for a Better Service Visit
If you are calling a contractor or Stiebel Eltron technical support, collect the following before the appointment: model number, serial number, breaker sizes, number of double-pole breakers, conductor sizes if known, setpoint, inlet water temperature, outlet temperature, measured hot-side gpm, water pressure if known, error code, and whether the power light blinks under high demand.
Also note the home’s main service size: 100 A, 125 A, 150 A, 200 A, 300 A, or other. This is especially important for Tempra 24, 29, and 36 Plus models. A service call goes much better when the technician can separate an appliance fault from an undersized installation.
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The Bottom Line
For Tempra Plus troubleshooting, start simple and measure. Check the model, breakers, flow rate, fixture restrictions, setpoint, and display state. If the heater works at one fixture but struggles under multiple fixtures, you may be seeing the limits of temperature rise or the unit’s Advanced Flow Control doing its job. If there is an error code, repeated breaker trip, suspected voltage drop, thermal cutout issue, or need to open the cover, bring in a licensed plumber or electrician.
That approach protects the homeowner, avoids unnecessary parts, and gets to the real cause faster: power, flow, capacity, scale, plumbing orientation, or a genuine internal fault.
Frequently Asked Questions
Why is my Stiebel Eltron Tempra Plus not making hot water?
Common causes include breakers turned off, insufficient flow to activate the heater, a clogged inlet filter, clogged faucet aerator or shower head, reversed hot and cold plumbing, a stuck flow sensor, or an internal fault. Start by checking all dedicated breakers, measuring hot-side flow, and recording any display error code.
What do Tempra Plus error codes 2 and 3 mean?
Error 2 indicates an inlet temperature sensor failure. Error 3 indicates an outlet temperature sensor failure and may involve the outlet sensor cable connection. Record the code, model, serial number, flow rate, and setpoint, then contact Stiebel Eltron technical support or a licensed technician.
Can I reset a Tempra Plus water heater myself?
You can safely reset external breakers if your panel is accessible and labeled. Internal thermal cutout resets require all breakers feeding the unit to be completely off and should be handled by a licensed pro because the trip may indicate overheating, scale, low flow, wiring trouble, or component failure.
Why does my Tempra Plus only get lukewarm during showers?
The most common reason is that fixture demand exceeds the heater’s temperature-rise capacity. A 24 kW unit at 240 V can raise about 3.0 gpm by roughly 54 F. Cold incoming water, high-flow shower heads, multiple fixtures, scale buildup, or low voltage under load can all cause lukewarm water.
How often should a Tempra Plus be descaled in hard-water areas?
In hard-water homes, plan on descaling every 6 to 12 months. Very hard water may require more frequent service or water treatment. Scale on heating elements can reduce performance, shorten service life, and contribute to overheating problems.
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Permit rules are local. Many jurisdictions require a water-heater replacement permit, and tankless electric units may involve both plumbing and electrical review. Example 2026 permit references range from about $103 to $180 in some cities, but your local AHJ controls the actual requirement and fee.
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Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
