Kaisai F4 fault code

What it means

Safety: Safe isolation, then TREAT THE DC LINK AS LIVE. The electrolytic capacitors hold a lethal charge after the supply is off. Discharge through a suitable resistor across the + and − terminals and confirm with a meter on DC before touching the board. Never short the terminals with a screwdriver.

Source: KAISAI FLY Inverter Series B (KWX) R32 service manual, §4 Quick Maintenance by Error Code (p.65, render-verified) + §5 Troubleshooting by Error Code

UK models this code applies to

Tap yours to open F4 on that machine.

Now the harder half: proving what caused it

F4 names a symptom, not a root cause. In the app, the same code opens a guided investigation: what to measure first, the expected values for your exact model, and an honest verdict — including “nothing in this machine is broken” when that's what the readings say.

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