Run capacitor
Common no-start and weak-compressor failure point. Match the microfarad and voltage rating.
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 - Ignition Failure
Check gas supply pressure at the inlet (3.5-5 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 - 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 - 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 - 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 | Annual replacement |
| Inlet/outlet sensors | Check resistance |
| Igniter | Check for cracks |
| Gas valve | Test coil resistance |
| Expansion tank | Check pre-charge before replacing |
| Circulation pump | Check for seized impeller |
Need Replacement Parts?
Before ordering, match the water-heating part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
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.