Aqua-Hot Furnace: “Fault Code 8”
warning RV furnace fault codes
What it means
The burner failed to ignite on its initial start attempt, or the right high-limit thermostat tripped. The controller ran the start sequence but the flame sensor never confirmed a flame, commonly due to a fuel-delivery problem, overheat, or low voltage during startup.
Most likely causes
- Inadequate fuel supply (low tank, air in fuel line, clogged fuel filter) most likely
- Faulty fuel solenoid or obstructed/contaminated fuel nozzle common
- Right high-limit thermostat tripped (overheat) or shorted to ground common
- Defective ignition module or incorrect combustion-air setting less common
- Supply voltage dropping below 11V DC during the startup cycle less common
Safe checks you can do yourself
- Confirm the vehicle's diesel fuel supply is adequate (this draws from the chassis tank, often via a standpipe so it can't run the tank dry)
- Check the fuel filter for clogging and the fuel nozzle for obstructions or contamination
- Test both high-limit thermostats for continuity and press the reset button if tripped
- Verify 12V stays above 11V during the start cycle
How to reset / clear Fault Code 8
- Correct the fuel, overheat or voltage condition first
- If a high-limit thermostat tripped, allow the unit to cool and press its white reset button
- Turn the diesel-burner switch OFF for about 30 seconds, then back ON to clear the fault and restart
When to call a technician
If fuel supply, filter, nozzle, thermostats and voltage are all good but ignition still fails, the ignition module or controller likely needs service. Contact a qualified technician or 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 8" mean?
The burner failed to ignite on its initial start attempt, or the right high-limit thermostat tripped. The controller ran the start sequence but the flame sensor never confirmed a flame, commonly due to a fuel-delivery problem, overheat, or low voltage during startup.
How do I reset Aqua-Hot Furnace Fault Code 8?
Correct the fuel, overheat or voltage condition first If a high-limit thermostat tripped, allow the unit to cool and press its white reset button Turn the diesel-burner switch OFF for about 30 seconds, then back ON to clear the fault and restart
What is the most common cause of Fault Code 8 on a Aqua-Hot Furnace?
The most likely cause is inadequate fuel supply (low tank, air in fuel line, clogged fuel filter).
Related · Aqua-Hot furnace
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Sources
- Aqua-Hot 375-D02 Hydronic Heating System Service Manual (Rev. E) — Section 9, Fault Code 8, p.95 (Aqua-Hot Heating Systems Inc.)
Note: Blink-count to fault mapping is specific to the 375-D02 controller; other Aqua-Hot generations differ.
● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.