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Sunsynk F08: GFDI Relay Failure

Updated June 2026 · Reviewed for technical accuracy · ~3 min read

F08 points at your Sunsynk's GFDI (Ground-Fault Detector Interrupter), the protection that watches for dangerous leakage to ground. Because this is a safety device, a real or repeated F08 deserves a proper check rather than endless resets. There is one common, safe thing to look at first: the neutral-to-ground bonding on the backup output.

What F08 usually means

  • Incorrect neutral-to-ground bonding on the backup output, common on split-phase and three-phase systems. The N line must be grounded as the Sunsynk manual specifies.
  • A ground-fault or leakage somewhere in the system that the GFDI caught.
  • A genuine fault in the GFDI relay or circuit itself.

What to do, safely

Before you start Grounding and bonding are protective wiring. The only owner-level steps are to note recent changes and to power-cycle once. Anything touching the N-to-ground bond or the internal relay is an installer job.
  1. Think about recent changes. Did F08 begin right after new wiring, a new backup connection, or an install change? That points straight at a bonding issue from the work.
  2. Power-cycle once. Turn off the AC breaker, then the DC isolator, wait five minutes, and restart. A one-off glitch may clear.
  3. If F08 returns, stop. Repeatedly clearing a ground-fault protection defeats its purpose.
  4. Call your installer. They verify the neutral-to-ground bonding against the Sunsynk manual for your system type, check for a real ground fault, and confirm the GFDI circuit is healthy.

Quick decision flowchart

F08 appears
↓ power-cycle once
✅ Clears and stays gone → likely a one-time glitch. Keep an eye on it.
❌ Returns → bonding or GFDI circuit issue. Don't keep resetting.
↓
Have your installer verify the N-to-ground bonding and check for a ground fault.
When to bring in a professional Any F08 that returns after a single restart should be inspected. It involves ground-fault protection, a safety function, so the correct response is a qualified check of the bonding and the GFDI circuit, not repeated resets.

Related Sunsynk codes

F24, DC insulation failure F23, AC leakage current F63, Arc fault

FAQ

F08 started right after my system was installed or changed.

Usually not a coincidence. A fresh F08 right after wiring work very often points to the neutral-to-ground bonding on the backup output. Ask whoever did the work to verify it against the Sunsynk manual for your configuration.

Can I keep using the system with F08 showing?

The GFDI is a safety protection. If it is flagging a fault, you shouldn't bypass or ignore it. Get it checked before relying on the system.

Is F08 the same as my house RCD tripping?

They are related in spirit (both detect leakage to ground), but F08 is the inverter's own ground-fault protection reporting an issue on the solar or backup side. The fix is on the inverter's grounding and circuit, not your household RCD.

Sources

  • Sunsynk Hybrid Inverter User Manual (F08 = GFDI relay failure; check backup load port N line connection to ground on split/three-phase systems).
  • Sunsynk fault-code references and installer documentation.
⚠️ Safety disclaimer. F08 involves ground-fault protection. Solar inverters carry lethal DC and AC voltage. This guide covers only noting recent changes and a single safe power cycle. Grounding, bonding, and internal relay checks must be done by a licensed installer or electrician.