Annual descaling is required to maintain warranty on Westinghouse tankless water heaters (gas and electric). Skipping descaling voids the heat exchanger warranty — which is the most expensive component.
When to descale
| Water hardness | Recommended frequency |
|---|---|
| Soft (0-5 gpg) | Every 2-3 years |
| Moderate (5-10 gpg) | Annually |
| Hard (10-15 gpg) | Annually + softener strongly recommended |
| Very hard (15+ gpg) | Softener required for warranty |
Symptoms requiring immediate descale
- E14 (overheat) fault codes on gas tankless
- Reduced output temperature despite normal gas pressure / electrical supply
- Audible popping or knocking from heat exchanger
- Reduced flow rate at hot taps over time
- "Cold sandwich" effect — short bursts of cold water during long hot draws
What you need
- Tankless descaling pump kit (Stiebel-compatible, Westinghouse OEM, or generic circulator with hoses)
- 2-3 gallons white vinegar OR commercial descaler (CLR, Rydlyme, or similar)
- Service shutoffs already installed (typical install includes these)
- Bucket for circulation
- Two hoses for inlet and outlet connections
Procedure (gas tankless WGRGH)
- Power OFF at the unit\'s breaker (120V control circuit)
- Close gas supply at the unit shutoff
- Close inlet and outlet shutoffs (cold supply and hot outlet)
- Open the service drain ports on the inlet and outlet shutoffs
- Connect descaling pump: inlet drain port → bucket → outlet drain port
- 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 inlet shutoff into bucket until pH neutral
- Open inlet shutoff fully. Run cold water through tankless for 2-3 minutes to flush
- Open outlet shutoff. Verify good flow
- Restore gas and power
- Test hot water at a fixture; verify temperature stability
Procedure (electric tankless WET)
Same general procedure with electrical specifics:
- Power OFF at ALL breakers. WET-18 has 2; WET-27 has 3; WET-36 has 4. Verify with voltage tester
- Close inlet/outlet shutoffs
- Connect descaling pump via service ports
- Circulate descaler 30-60 minutes
- Flush with fresh water until pH neutral
- Open shutoffs
- Restore power at ALL breakers
- Test operation
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. Used by contractors
- CLR: $20-30/gallon. Mid-grade; good for moderate scaling
What NOT to use
- Muriatic acid: too aggressive, damages stainless components
- Sulfamic acid high concentration: can damage seals
- Lye: alkaline, doesn\'t dissolve scale
Hard water solution: install a softener
For water above 10 gpg, descaling annually becomes a hassle. The math favors installing a whole-home water softener ($1,500-2,500):
- Eliminates descaling requirement
- Extends heat exchanger life
- Reduces sediment buildup throughout plumbing
- Preserves dishwasher and clothes washer life
- Maintains tankless warranty (Westinghouse requires softener at >7 gpg)
Bottom line
Annual descaling in hard water. Required for Westinghouse tankless warranty. White vinegar is adequate; commercial descaler is faster. Always power off all breakers (electric) or gas + breaker (gas) first. Hard water installs need a softener.