Pentair Max-E-Therm ERR HLS Error
The ERR HLS error on a Pentair Max-E-Therm indicates the high temperature limit switch has opened. This occurs when water temperature after the first pass through the heat exchanger exceeds 135F.
This error will auto-clear when the temperature falls below 135F.
What Causes ERR HLS?
The high limit switch is a safety device that prevents the heater from overheating the water. It opens when water temperature gets too high.
Common Causes
- Low water flow: Not enough water moving through heat exchanger
- Dirty filter: Restricting water flow
- Scale buildup: In heat exchanger reducing heat transfer
- Improper gas pressure: Too high causing excessive heat
- Failed high limit switch: Switch stuck or failing
- Oversized heater: Heater too large for the pool/spa volume
Troubleshooting Steps
Step 1: Allow Cool Down
- Turn off heater
- Keep pump running to circulate water
- Wait for water to cool below 135F
- Error should auto-clear
Step 2: Check Water Flow
- Verify pump is running properly
- Check filter pressure (clean if high)
- Ensure bypass valves are closed
- Confirm all isolation valves are open
Step 3: Inspect Heat Exchanger
Scale buildup reduces heat transfer efficiency:
- Look for signs of scale in visible areas
- Check water chemistry history (high calcium?)
- Professional descaling may be required
Step 4: Verify Set Point
- Check temperature set point on control panel
- Ensure it's not set excessively high
- Spa mode should not exceed 104F
Step 5: Check Gas Pressure
Requires qualified technician:
- Verify manifold pressure is correct for heater model
- Check gas regulator operation
- Inspect gas orifices for proper size
If Error Keeps Recurring
- Have heat exchanger professionally cleaned
- Test high limit switch
- Verify heater is properly sized for application
- Check for proper water chemistry maintenance
Prevention
- Maintain proper water chemistry (especially calcium and pH)
- Keep filter clean
- Run pump at adequate speed during heating
- Have heater inspected annually