Aqua-Hot Furnace: “Fault Code 1”
warning RV furnace fault codes
What it means
Low supply voltage detected by the diesel-burner controller. The 12V supply is below the minimum the controller needs (about 11.1V) either at startup or during the burner cycle, so the system shuts the burner down to protect it.
Most likely causes
- House/chassis battery voltage drops below about 11.1V most likely
- Voltage starts adequate but sags below 11.1V during the burner's run cycle (weak battery, high load) common
- Poor or corroded 12V power/ground connections to the burner controller less common
Safe checks you can do yourself
- Measure 12V battery voltage and confirm it stays above 11.1V at rest
- Run the burner cycle while monitoring voltage at the controller to see if it sags under load
- Charge or recharge the house batteries and retest
- Inspect 12V power and ground connections for corrosion or looseness
How to reset / clear Fault Code 1
- Restore adequate battery voltage (charge batteries, reduce load, connect to shore power/generator)
- Turn the diesel-burner switch OFF for about 30 seconds
- Turn the switch back ON to clear the blinking fault and restart
When to call a technician
If battery voltage is confirmed healthy and stable above 11.1V but the low-voltage fault keeps recurring, have the controller and wiring inspected or call Aqua-Hot Technical Support at 1-800-685-4298.
Applies to
Aqua-Hot 375-D02 · AHE-375-D02
FAQ
What does Aqua-Hot Furnace code "Fault Code 1" mean?
Low supply voltage detected by the diesel-burner controller. The 12V supply is below the minimum the controller needs (about 11.1V) either at startup or during the burner cycle, so the system shuts the burner down to protect it.
How do I reset Aqua-Hot Furnace Fault Code 1?
Restore adequate battery voltage (charge batteries, reduce load, connect to shore power/generator) Turn the diesel-burner switch OFF for about 30 seconds Turn the switch back ON to clear the blinking fault and restart
What is the most common cause of Fault Code 1 on a Aqua-Hot Furnace?
The most likely cause is house/chassis battery voltage drops below about 11.1v.
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Sources
- Aqua-Hot 375-D02 Hydronic Heating System Service Manual (Rev. E) — Section 9, Fault Code 1, p.94 (Aqua-Hot Heating Systems Inc.)
Note: Exact voltage thresholds and blink assignments are from the 375-D02 manual; other Aqua-Hot models may use different thresholds.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.