Eemax Booster Heater Error Code F3: Excessive Dry Fire Events

What does Eemax error code F3 mean?

F3 builds on F2. A single dry fire event gives F2. When the control counts too many of them, it shows F3 for excessive dry fire occurrences and shuts the heater down immediately. The screen alternates F3 with SETPOINT every 3 seconds. The manual does not state how many events count as excessive, and it lists no cause beyond the condition named. What the pattern tells you is that the water supply to the heater has been unreliable more than once, whether from air in the line, an intermittent shutoff or a clogged inlet. The manual's instruction is to call Eemax Technical Support. The elements may already have been stressed by the repeated dry running, so this is a case where a technician checks the heater itself and the plumbing before any further use.

Affected models and control systems

This code is for the Eemax SpecAdvantage and SafeAdvantage electric tankless heaters with the LCD control, and it follows F2 in the manual's list. The manual does not call these units boosters.

Code numbers and their meaning can change between control generations. We match the full model and control before acting on a code.

What you may notice

• F3 alternating with SETPOINT
• Heater off and not responding to a new setpoint
• Earlier F2 shutdowns
• Intermittent water at the outlet

Possible causes

Listed in Eemax's documentation

• Excessive dry fire occurrences detected

Other likely causes — what usually sits behind error code F3 on this control. A technician confirms which one it is before any part is replaced.

• Air repeatedly entering the supply line from a pump, tank or leak
• Supply valve or float arrangement that shuts the water off at intervals
• Partly blocked inlet strainer starving the heater of water

Safe checks before calling for service

How a technician diagnoses error code F3

1. Read the history for the number and timing of dry fire events.
2. Check the water supply for air, pressure drops and shutoffs.
3. Inspect the inlet strainer and valve.
4. Test the heating elements for damage with a meter.
5. Check the optical sensor and its connection.
6. Fix the supply problem, then restore power with the heater full and verify operation.

How error code F3 differs from similar codes

F3 is the repeat of F2. A single dry fire event shows F2, and several show F3.

Technical reference

Document

Installation, Operation, and Maintenance Manual for Electric Tankless Water Heaters: SpecAdvantage | SafeAdvantage

Edition

EX07200-15 Rev 9 (footer; 80 pp)

Models / control

Eemax SpecAdvantage / SafeAdvantage electric tankless water heaters with LCD control (the manual mentions sanitation models in circulator systems; it does not c

Section

Operating instructions, step 12 'Fault Codes', p. 17

Checked

October 2026

We use the maker's document to read the code and do not reproduce it. Always confirm the complete model and control before applying these steps.