Many thanks for your replies. I suspect that it is a grid problem as I live in a rural area close to the transformer which probably accounts for the high voltage.
I have a Solis 3.6 KW inverter which works well until it exceeds about 2000W when it shows "over grid voltage" and shuts down. This does not happen if something is switched on in the house which draws a large amount of current such as the immersion heater. I have a voltage meter in the house...
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