What Error 4xx Means
Error 4xx appears when your W&H Lisa sterilizer detects one of these problems:
- Low water level in the clean water tank
- Poor water quality (contamination, mineral buildup, or non-compliant water type)
- Unacceptable water condition that affects sterilization performance
This is the most common error in dental practices—and the good news? It's almost always fixable in 5 minutes.
Step-by-Step Troubleshooting (5 Minutes)
Step 1: Check the Clean Water Tank Level
- Open the sterilizer door (after the chamber has cooled)
- Locate the clean water tank (sits on top or side of the unit)
- Check the water level against the MIN and MAX marks on the tank
- If below MIN: refill immediately with distilled water
- Close the door and restart the sterilization cycle
Step 2: Check Your Water Type
- ✓ Use: Distilled water or reverse osmosis (RO) water ONLY
- ✗ Do NOT use: Tap water, bottled water, mineral water, or filtered water
Why? Minerals in tap water clog the water line and contaminate your steam.
Prevent Error 4xx: Weekly Water Checks
Add this 2-minute task to your weekly sterilizer maintenance:
- Check clean water tank level—refill if below MIN mark
- Verify you're using distilled or RO water ONLY
- Visually inspect the tank for cloudiness or sediment
- Check the drain water tank—empty if needed
- Look for any leaks around water connections