Hard water scales the heating elements and internal passages of all electric tankless units. Annual descaling in hard water keeps your Tempra Plus performing at rated capacity and extends element life.
When to descale
| Water hardness | Descaling frequency |
|---|---|
| 0-5 gpg (soft) | Every 3-4 years |
| 5-10 gpg (moderate) | Every 2 years |
| 10-15 gpg (hard) | Annually |
| 15+ gpg (very hard) | Annually + water softener strongly recommended |
Symptoms requiring immediate descale
- Reduced flow rate at hot taps over time
- Output temperature dropping below setpoint despite adequate kW capacity
- Breaker trips under load that weren\'t happening before (scaled element draws more amps)
- Audible popping or hissing from the unit (boiling on scale-insulated elements)
What you need
- Descaling pump kit (Stiebel-compatible isolation kit OR generic circulator pump with hoses)
- 2-3 gallons white vinegar OR commercial descaler (Rydlyme, CLR, or similar)
- Bucket for circulation
- Two hoses for inlet and outlet connections
Procedure
- Power OFF at all breakers. Verify with voltage tester — Tempra Plus has multiple double-pole breakers; all must be off
- Close shutoff valves on the inlet and outlet (most Tempra installs ship with these; if not, install before descaling)
- Open hot tap downstream briefly to relieve pressure
- Connect descaling pump: drain port to inlet shutoff; outlet shutoff to bucket return
- Pour 2-3 gallons descaler into bucket
- Start pump. Circulate for 30-60 minutes. You\'ll see foam forming as scale dissolves
- Stop pump. Disconnect descaling rig
- Flush with fresh water via the inlet shutoff into the bucket until pH neutral (no foaming when tested with descaler)
- Open inlet shutoff fully. Run cold water through Tempra for 2-3 minutes to fully flush
- Open outlet shutoff. Verify good flow through the unit
- Restore power at all breakers
- Test hot water at a fixture; verify output temperature meets setpoint
Vinegar vs commercial descaler
- White vinegar: $3-5/gallon at grocery store, food-safe, mild. Adequate for annual maintenance descaling. Slower acting; needs longer circulation
- Rydlyme: $35-50/gallon. Faster acting, professional-grade, slightly more aggressive on heavy scale. Used by contractors
- CLR: $20-30/gallon. Mid-grade; good for moderate scaling
What NOT to use
- Muriatic acid (hydrochloric acid): too aggressive, damages stainless components
- Sulfamic acid in high concentration: can damage seals and gaskets
- Lye / sodium hydroxide: alkaline; doesn\'t dissolve scale (which is alkaline)
If descaling doesn\'t restore performance
Severe scale that has bridged across heating elements may require element replacement, not just descaling. After descaling:
- Test each element with ohm meter (Tempra Plus has multiple elements depending on size)
- Healthy element: 4-15 Ω depending on wattage
- Open (OL) or shorted (near 0) = replace
- See element test guide
Prevention is better than cure
In 10+ gpg water, the math favors installing a whole-home water softener ($1,500-2,500) over annual descaling and shortened element life. Softeners pay back through extended water heater life, longer dishwasher and washing machine life, reduced soap and detergent usage, and preserved fixture finishes.
Bottom line
Annual descaling in hard water. White vinegar is adequate; commercial descaler is faster. Always power off all breakers first. After descaling, test element resistance — descaling can\'t resurrect a burnt element.