Descaling is the most important maintenance task for tankless water heaters. Mineral buildup in the heat exchanger reduces efficiency, causes error codes, and can lead to expensive repairs. Here's what Mount Pleasant, Charleston, and Daniel Island homeowners need to know.
Why Tankless Water Heaters Need Descaling
How Scale Forms
Even in moderately hard water (like Charleston's), minerals accumulate inside the heat exchanger over time. When water is heated, calcium and magnesium precipitate out and coat the internal surfaces.
What Scale Does
Reduces Efficiency: Scale insulates the heat exchanger, requiring more energy to heat water.
Restricts Flow: Buildup narrows water passages, reducing flow rate.
Causes Overheating: Poor heat transfer leads to elevated temperatures and error codes.
Damages Components: Severe scale can crack heat exchangers, requiring expensive replacement.
Signs Your Tankless Needs Descaling
Error Codes
Most tankless units display error codes when scale causes problems:
| Brand | Common Scale-Related Codes |
|---|---|
| Navien | E003, E004, E110 |
| Rinnai | 11, 12, LC (lime/scale) |
| Rheem | Various overheat codes |
| Noritz | 11, 12, 16 |
Check your owner's manual for specific code meanings.
Performance Issues
- Hot water temperature fluctuates
- Flow rate has decreased
- Unit cycles on and off rapidly
- Takes longer to get hot water
- Lower maximum temperature
Time-Based
Even without symptoms, descale annually to prevent problems.
How Often to Descale
| Water Hardness | Descaling Frequency |
|---|---|
| Soft (0-3 GPG) | Every 2 years |
| Moderate (3-7 GPG) | Annually |
| Hard (7-10 GPG) | Every 6-9 months |
| Very Hard (10+ GPG) | Every 4-6 months |
Charleston Area Recommendation: Annual descaling for most homes. Charleston's moderately hard water (3-5 GPG) means yearly service keeps units running well.
Coastal Properties (Sullivan's Island, Isle of Palms): Annual descaling, possibly more frequently if you notice reduced performance.
Professional vs. DIY Descaling
Professional Descaling
Cost: $150-$300 Time: 45-90 minutes Includes:
- Full descaling with commercial solutions
- System flush
- Inspection of components
- Error code clearing
- Performance verification
Pros:
- Thorough cleaning
- Identifies other issues
- No risk of damage
- May be required for warranty
DIY Descaling
Cost: $50-$100 (equipment and solution) Time: 1-2 hours
Required Equipment:
- Submersible pump
- Two 5-gallon buckets
- Descaling solution (white vinegar or commercial)
- Hoses to connect to isolation valves
Pros:
- Lower cost
- Can do on your schedule
Cons:
- Requires isolation valves (most units have them)
- Risk of improper procedure
- Doesn't include professional inspection
DIY Descaling Steps
Prerequisites
Your tankless must have isolation valves (most modern units do). If not, professional service is required.
What You'll Need
- Submersible pump (1/6 HP sump pump works)
- Two 5-gallon buckets
- Two washing machine hoses or similar
- 2-3 gallons white vinegar OR commercial descaler
- Screwdriver to open access panel
Step-by-Step Process
Step 1: Prepare
- Turn off gas supply (or power for electric)
- Turn off cold water supply to unit
- Close hot water isolation valve
Step 2: Connect Hoses
- Connect hose from pump to cold water service port
- Connect hose from hot water service port to bucket
- Place pump in second bucket
Step 3: Add Descaling Solution
- Pour 2-3 gallons white vinegar into pump bucket
- Commercial descalers work faster but cost more
Step 4: Circulate
- Turn on pump
- Solution circulates through heat exchanger
- Continue for 45-60 minutes (vinegar) or per product instructions
- Solution should flow freely; reduced flow indicates blockage
Step 5: Flush
- Remove pump from solution
- Place in bucket of clean water
- Flush for 5-10 minutes to remove descaler
Step 6: Restore
- Remove hoses
- Close service ports
- Open isolation valves
- Turn on gas/power and water
- Test operation
Commercial Descaling Solutions
White Vinegar
Pros:
- Cheap and readily available
- Food-safe
- Effective for light to moderate scale
Cons:
- Slower acting (45-60 minutes)
- Less effective on heavy scale
- Strong smell
Commercial Descalers
Flow-Aide, Calci-Free, etc.
Pros:
- Faster acting (15-30 minutes)
- More effective on heavy scale
- Less odor
Cons:
- More expensive ($15-$30)
- Must be thoroughly flushed
Preventing Scale Buildup
Scale Inhibitors
Inline scale inhibitors reduce (but don't eliminate) scale formation.
Cost: $100-$200 installed Effectiveness: Extends time between descaling
Water Softener
Whole-house softener virtually eliminates scale.
Cost: $1,500-$4,000 installed Effectiveness: Near-complete scale prevention
Lower Temperature Setting
Higher temperatures accelerate scale formation. Setting output temperature to 120°F instead of 140°F reduces scale.
What Happens If You Don't Descale?
Short-Term (1-2 Years)
- Gradually reduced efficiency
- Higher gas/electric bills
- Slightly reduced flow
Medium-Term (3-5 Years)
- Error codes appear
- Significant flow reduction
- Unit may shut down
- Intermittent hot water
Long-Term (5+ Years)
- Heat exchanger damage
- Expensive repairs ($500-$1,500)
- Premature unit failure
- Complete replacement needed
Heat Exchanger Replacement Costs
If descaling is neglected too long:
| Component | Cost |
|---|---|
| Heat exchanger (part) | $300-$800 |
| Labor | $200-$400 |
| Total | $500-$1,200 |
Compare to annual descaling: $150-$300/year
Warranty Considerations
Many manufacturers require documented annual maintenance for warranty coverage. Check your warranty terms. Navien, Rinnai, and other major brands may void coverage if scale damage results from lack of maintenance.
Service Areas
Water Heater Doctors provides professional tankless descaling throughout the Charleston Lowcountry:
Mount Pleasant - All neighborhoods. Daniel Island - Residential and commercial. Charleston - Downtown, West Ashley, James Island. Sullivan's Island - Full service. Isle of Palms - Including Wild Dunes.
FAQ: Tankless Descaling
How do I know if my tankless needs descaling? Error codes, reduced flow, temperature fluctuations, or it's been over a year since last service.
Can I use CLR or other household cleaners? White vinegar is safe. Commercial descalers designed for tankless are ideal. Avoid harsh chemicals not designed for this purpose.
How long does descaling take? DIY: 1-2 hours. Professional service: 45-90 minutes.
Do all tankless water heaters need descaling? Yes, all tankless units accumulate scale. Some water conditions cause faster buildup than others.
What if descaling doesn't fix my error code? Scale may have caused damage, or there's an unrelated issue. Professional diagnosis is recommended.
Keep your tankless running efficiently with regular descaling. Water Heater Doctors provides professional descaling service throughout Charleston, Mount Pleasant, Daniel Island, Sullivan's Island, and Isle of Palms. Call (843) 990-6524 to schedule your annual maintenance.