Growatt Error 101 — Internal CPU Communication Fault (TL / MTL grid-tied)

What it means: The two CPUs inside the inverter have lost communication with each other. Growatt's TL and MTL troubleshooting guide groups Error 101 with Error 121 for this meaning, and gives Error 102 for the closely related case where the two CPUs' sampled data disagree. This is an internal electronics fault on the control board. It is not a grid fault — nothing about your grid supply, your panels or your protection settings causes it, and changing them will not clear it.

Why does Growatt show 101?

• Loss of communication between the inverter's two CPUs, which Growatt resolves by replacing the control board
• A one-off glitch that clears on a complete power-down, which is Growatt's first step
• The related Error 102, where the two CPUs sample inconsistent data — same board, same escalation path

The Pakistan factor

Growatt's TL and MTL grid-tied units are the older generation still running on many early Pakistani net-metered rooftops, and control-board faults on them are usually out of warranty by now. Get a repair quote before assuming the whole inverter has to go. Heat is the aggravating factor here — an intermittent 101 that appears on hot afternoons and clears overnight is a board failing thermally, and it will get worse through the summer rather than settle down. One important caution before you match this code to your unit. The newer Growatt hybrid and three-phase ranges use completely different code sets. The MOD three-phase manual, for example, has no 100-series system errors at all — its faults start at Error 200. A three-digit code on a MIN, MOD or SPH does not mean what it means here, so check your model number first.

How to fix it

1. Safe for a homeowner — do the one restart Growatt asks for. Turn the DC switch off and let the inverter shut down completely, until the screen is dark. Then turn the DC switch back on and see whether the error returns.
2. Safe for a homeowner — note the timing. Does it come back immediately, after a few hours, or only on hot afternoons? That pattern is what a service engineer needs and it is the difference between a board that has failed and one that is failing thermally.
3. Do not go looking for the cause in your grid supply or your array. This is not a grid or PV fault. Widening voltage windows or changing the country setting will not clear 101 and can leave your system running with the wrong protection settings, which is a real hazard on a net-metered rooftop.
4. If the fault survives the restart, Growatt's next step is replacing the control board. That board sits behind the RS232 port alongside the DC bus capacitors, which hold a lethal charge after shutdown. Do not open the inverter. This is a Growatt service action.
5. Contact Growatt service or your installer with the model number, the exact code and the timing pattern you recorded. Growatt's guide stops at the control board for 101 — for the neighbouring Error 100 it goes on to replacing the whole inverter if a new board does not clear it, so keep your fault log either way; it is your warranty evidence.