E1 = no water flow detected. The flow sensor reports flow below the activation threshold (~0.5 GPM on most Tempra Plus models). Unit won\'t energize heating elements without flow detection.
Diagnostic sequence
1. Verify actual flow at a fixture
- Open a hot tap fully
- Catch flow in a 1-gallon bucket and time it
- Under 30 seconds = 2+ GPM = adequate
- Over 60 seconds = below 1 GPM = inadequate; check supply
2. Clean inlet filter (#1 cause)
Tempra Plus has a fine inlet strainer at the cold water connection. Debris from new construction, old galvanized plumbing, or hard water scale clogs it. Procedure:
- Close inlet shutoff
- Unscrew the filter cap or service fitting at the inlet
- Remove strainer, rinse, inspect for damage
- Reinstall
- Reopen shutoff; verify flow restored
3. Restricted aerator at fixture
Low-flow aerators on bathroom faucets (0.5 GPM) may not exceed Tempra\'s activation threshold. Verify at a non-restricted tap (kitchen, tub).
4. Closed shutoff somewhere upstream
Recent service may have left a shutoff partially closed. Trace from meter through main shutoff to Tempra inlet shutoff.
5. Pressure regulator failed
House pressure regulator failing can drop inlet pressure below threshold. Test static pressure at a hose bib — should be 40-80 PSI.
6. Flow sensor failure (less common)
The flow sensor inside Tempra (impeller with hall sensor) may stick or fail. After confirming flow IS adequate at the unit inlet, this is the next suspect. Contractor diagnosis with multimeter on sensor lead.
Reset E1
- Address the flow issue (filter clean, shutoff open)
- Power cycle: breakers off 30 seconds, then on
- Open a hot tap; verify flow and ignition
Bottom line
Most E1 cases: clogged inlet filter. 10-minute cleaning fix. If filter is clean and flow is verified at the unit, suspect flow sensor and call Stiebel tech support.