Fault Code 0 (1 blink)

Aqua-Hot Furnace: “Fault Code 0 (1 blink)”

warning RV furnace fault codes

Safety The diesel burner uses 120V AC and 12V DC and produces hot combustion exhaust. Disconnect 120V AC shore/generator power before any servicing to avoid electric shock. The interlock that disables the burner with the cover off is a safety device; never bypass it, and never operate the burner with the exhaust path blocked, since diesel combustion produces carbon monoxide.

What it means

The diesel-burner indicator light is not lit even though the diesel-burner switch is ON. The controller is not receiving the conditions it needs to power up the burner, usually because a safety interlock is open or 12V power is missing.

Most likely causes

Access cover removed, so the interlock safety switch keeps the burner disabled most likely
Blown fuse for the diesel-burner switch or no 12V power at the burner controller common
Coolant/antifreeze low-level float switch tripped common
Interlock switch wiring disconnected or interlock switch has no continuity less common

Safe checks you can do yourself

Confirm the burner access cover is fully installed and seated so the interlock switch is held closed
Check the diesel-burner fuse (B-fuse) on the fuse block for 12V power
Verify the coolant/antifreeze level in the expansion tank is not low enough to trip the float switch
Inspect the interlock switch wiring for loose or disconnected connectors

How to reset / clear Fault Code 0 (1 blink)

Correct the underlying condition first (replace fuse, refit cover, top up fluid)
Turn the diesel-burner switch OFF for about 30 seconds
Turn the diesel-burner switch back ON and watch whether the indicator light illuminates

When to call a technician

If 12V power, fuse, fluid level and interlock all check out but the burner still will not power up, or if you are not comfortable testing the float/interlock switches, contact 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 0 (1 blink)" mean?

How do I reset Aqua-Hot Furnace Fault Code 0 (1 blink)?

Correct the underlying condition first (replace fuse, refit cover, top up fluid) Turn the diesel-burner switch OFF for about 30 seconds Turn the diesel-burner switch back ON and watch whether the indicator light illuminates

What is the most common cause of Fault Code 0 (1 blink) on a Aqua-Hot Furnace?

The most likely cause is access cover removed, so the interlock safety switch keeps the burner disabled.

Related · Aqua-Hot furnace

Fault Code 1
Low supply voltage detected by the diesel-burner controller.… Fault Code 8
The burner failed to ignite on its initial start attempt, or… Fault Code 9
Re-ignition failure. The burner lit and established a flame,…

Sources

Aqua-Hot 375-D02 Hydronic Heating System Service Manual (Rev. E) — Section 9: Switch Panel Blinking Fault Indicator Light, Fault Code 0, p.94 (Aqua-Hot Heating Systems Inc.)

Note: Aqua-Hot indicates faults by a counted blink sequence rather than a numeric display; this manual is for the 375-D02 model and blink-count assignments can differ on other Aqua-Hot models and controller generations.

● Last verified 2026-06-29 · compiled from manufacturer documentation. Codes can vary by model year — always cross-check your unit’s manual.