E01 = ignition trial failed after the configured number of attempts (typically 3-5). The control locks out for safety. Most common Westinghouse WGRGH fault code.
Diagnostic sequence
1. Verify gas supply
- Gas shutoff at meter and at tankless unit — both fully open
- Other gas appliances working (range, dryer, furnace) — confirms gas to the house
- LP tank not empty (if propane application)
2. Inspect inlet water filter
Westinghouse WGRGH includes an inlet water filter. Clogged filter restricts flow below activation threshold; control may report E01 ignition failure because flow sensor never confirmed adequate flow before ignition attempt.
- Close inlet shutoff; relieve pressure
- Remove filter housing; pull strainer
- Rinse, soak in vinegar if scaled
- Reinstall
3. Inspect igniter electrode
- Pull burner cover (after gas off)
- Visual: gap between electrode and ground ~0.10-0.12"
- Eroded or cracked = replace
- Carbon deposits = clean with steel wool
4. Clean flame sensor
- Flame sensor near burner detects flame presence via rectification
- Oxidation on sensor = control thinks flame failed even when present
- Clean with fine sandpaper or steel wool — most common 5-minute fix
5. Verify gas pressure
- Manometer test at gas valve inlet under fire
- 7" WC natural gas; 11" WC propane
- Low pressure = undersized gas line, regulator failed, or LP tank cold/empty
6. Vent intake check
- Blocked PVC intake reduces combustion air
- Inspect intake termination for debris, snow, insect nests
Most common quick fixes
- Dirty flame sensor — clean with sandpaper. 5-minute resolution
- Clogged inlet water filter — clean. 10-minute resolution
- Closed gas shutoff — homeowners sometimes leave it closed after service
Reset
- Press Reset button on control display
- If E01 returns immediately = persistent fault; don\'t keep resetting
Bottom line
Most E01 cases: dirty flame sensor or clogged inlet filter. Both annual-service items. Annual descaling and inlet filter cleaning prevent most E01 events. Persistent E01 = gas pressure issue or gas valve.