GoodWe Inverter Error 21 — What to Do Next

What this code means

GoodWe's documentation lists this fault as “DC Bus High: BUS voltage is over-high.” Inside your inverter, the DC bus is the internal high-voltage rail that sits between the solar input stage and the grid output stage, and its voltage is tightly regulated by the inverter's control electronics. When that regulation fails — or when a surge drives the bus above its limit — the inverter trips error 21 and stops operating rather than risk damage to its power components. You cannot see or measure the DC bus from outside; it is entirely internal.

GoodWe's own troubleshooting for this fault is deliberately short: restart the inverter, and if the fault persists, contact GoodWe or your local service office. That brevity tells you something important — there is no user-serviceable cause and no deeper homeowner procedure. A transient bus overvoltage can follow grid disturbances, sudden load changes, or lightning-induced surges. A repeating fault, on the other hand, points to failing internal components such as ageing bus capacitors or a faulty control board. One detail worth knowing: because the bus is internal, this fault never means anything about your panels or your roof wiring — the problem, if there is one, is inside the inverter's own enclosure.

Treat a single error 21 like a tripped circuit breaker: note it, restart once, and watch. Treat a repeating error 21 as the unit telling you something inside is wrong. Do not keep force-restarting it — each restart into a genuine internal fault risks further damage, and the fault will keep returning until the hardware is repaired or the unit is replaced. If the inverter is still under warranty, a repeating error 21 is exactly the kind of fault warranty service exists for — document the dates and call it in rather than living with it.

Common causes

• Grid disturbance or surge — a sudden grid event can drive the internal bus voltage above its limit as a one-off.
• Ageing DC bus capacitors — capacitors degrade over the years and lose their ability to keep the bus voltage smooth and stable.
• Control board or regulation circuit fault — if the circuit that regulates bus voltage fails, the fault repeats on every start.
• Lightning-induced transient — a nearby strike can couple a surge into the system and trip the bus protection.
• Long-term thermal stress on power electronics — years of heat cycling can degrade internal components until regulation fails.