Fault codes / Aqua-Hot / LOW BATTERY VOLTAGE (red)

Aqua-Hot: Low battery voltage (red)

What it means: 12V too low.

What to check

Burner shut down. MUST be manually reset after voltage is restored: burner switch off ~30 seconds then on, or press the Low Voltage Reset button through the faceplate hole with a non-metal pick.

Learn the system

• Furnace sequence
• LP system basics

Practice it on a service call

• Furnace blows cold
• Furnace sparks but never lights
• Furnace keeps shutting off, fan keeps blowing

Guided diagnosis

• Furnace
• Thermostat

Other Aqua-Hot codes

• Aqua-Hot: Low tank-level cutoff (red) Boiler fluid low
• Aqua-Hot: Overload (red) 12V short or controller overheated
• Aqua-Hot: Zone light red Short in that zone
• Aqua-Hot: Pump #1/#2/#3 red Short in that pump circuit
• Aqua-Hot: Engine preheat red Short in the preheat pump circuit
• Aqua-Hot: Electric element red Short in the element's 12V control circuit

Full field guide: Aqua-Hot 450 hydronic heater

Codes come from the maker manuals and public service sheets. Your model's own chart always wins, and LP and 120 volt work belongs to a qualified technician.