Weil-McLain Ultra Series Boiler Error Codes
Weil-McLain Ultra series condensing boilers use a built-in diagnostic display that shows error codes on the front panel. The Ultra controls also store fault history accessible via the service menu.
Ultra Series Error Code Table
| Code | Fault Description | Common Cause | Action |
|---|---|---|---|
| E01 | Ignition failure | No gas, spark, or sensor | Check gas pressure and igniter |
| E02 | Flame loss | Gas pressure instability | Check gas supply |
| E03 | High limit | Boiler overheating | Check pump, flow rate, thermostat |
| E04 | Condensate backup | Clogged condensate drain | Clear condensate line |
| E05 | Flue temp high | Blocked flue or combustion issue | Inspect flue and heat exchanger |
| E06 | Low water pressure | Pressure below 10 PSI | Add water, check expansion tank |
| E07 | Outlet temp sensor | Failed outlet sensor | Check and replace sensor |
| E08 | Inlet temp sensor | Failed inlet sensor | Check and replace sensor |
| E09 | Return temp sensor | Failed return sensor | Check sensor wiring |
| E10 | Stack temp sensor | Flue temp sensor failure | Check sensor wiring |
| E11 | Combustion air/vent fault | Blocked intake or vent | Inspect intake and exhaust |
| E12 | Fan fault | Failed combustion fan | Check fan amps and RPM |
| E13 | Gas valve fault | Gas valve failure | Check valve voltage and resistance |
| E14 | Low gas pressure | Gas supply issue | Check supply and regulator |
| E15 | High gas pressure | Gas pressure too high | Check regulator setting |
Most Common Ultra Series Faults
E01 ΓÇö Ignition Failure
Check gas supply pressure at the inlet (3.5ΓÇô5 in. w.c. natural gas). Verify gas valve opens on call for heat. Check igniter electrode for cracks or carbon buildup. Clean flame sensor rod.
E03 ΓÇö High Limit
Ultra boilers require adequate flow to prevent overheating. Check system pump operation, verify all zone valves are not stuck closed, and confirm expansion tank pre-charge is correct (typically 12 PSI for residential).
E04 ΓÇö Condensate Backup
The Ultra is a condensing boiler producing up to 2 gallons of condensate per hour at full fire. The neutralizer cartridge and drain line must be clear. Replace neutralizer media annually. Check drain line for kinks or obstructions.
E06 ΓÇö Low Water Pressure
The Ultra will lockout below 10 PSI system pressure. Check for system leaks, waterlog expansion tank (drain tank, verify pre-charge = cold fill pressure, typically 12 PSI), and check backflow preventer fill valve operation.
Parts Commonly Needed
| Part | Notes |
|---|---|
| Neutralizer cartridge | Amazon | Annual replacement |
| Inlet/outlet sensors | Amazon | Check resistance |
| Igniter | Amazon | Check for cracks |
| Gas valve | Amazon | Test coil resistance |
| Expansion tank | Amazon | Check pre-charge before replacing |
| Circulation pump | Amazon | Check for seized impeller |
Pro tip: Weil-McLain Ultra boilers store up to 10 fault codes with timestamps. Access via Service → Fault History menu on the display. Reviewing fault timestamps helps identify whether faults are intermittent or consistent with specific heating demand patterns.