Girard Water Heater: “E4”
warning RV water heater fault codes
What it means
The inlet (cold side) water temperature sensor reads an invalid value while water is flowing. The board detects an open or shorted inlet temperature probe and faults out.
Most likely causes
- Loose or disconnected inlet temperature probe connector most likely
- Damaged inlet probe wiring common
- Failed inlet temperature probe (open or shorted) common
- Faulty control board input rare
Safe checks you can do yourself
- With power off, reseat the inlet temperature probe connector and check for corrosion.
- Inspect the inlet probe wiring for damage.
- If you have a multimeter, verify the probe is not a dead open or short.
How to reset / clear E4
- Turn the heater off at the panel.
- Cycle the 12V power off for ~10 seconds, then on.
- Turn the heater back on and run hot water to test.
When to call a technician
If reseating and a power cycle do not clear E4, have a technician test and replace the inlet probe or board.
Applies to
GSWH-2 · 2GWHAM
FAQ
What does Girard Water Heater code "E4" mean?
The inlet (cold side) water temperature sensor reads an invalid value while water is flowing. The board detects an open or shorted inlet temperature probe and faults out.
How do I reset Girard Water Heater E4?
Turn the heater off at the panel. Cycle the 12V power off for ~10 seconds, then on. Turn the heater back on and run hot water to test.
What is the most common cause of E4 on a Girard Water Heater?
The most likely cause is loose or disconnected inlet temperature probe connector.
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Sources
- Girard GSWH-2 Tankless Water Heater Technical Manual and Troubleshooting Guide — Fault code list, E4 Water Inlet Temperature Probe failure / input thermistor open when flow sensor active (Manuals.plus)
- Girard Products GSWH-2 Technical Manual — GSWH-2 Technical Manual, inlet temperature probe troubleshooting (Girard Products / ManualsLib)
Note: Described variously as 'water inlet temperature probe failure' and 'input thermistor open when the flow sensor is active' — same fault, slightly different wording across sources.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.