iBoost goes dead and then a few days later, comes to life again

[Lululily]

For the last few weeks, my iboost seems to completely switch off and even if you push any of the buttons or turn the switch to the mains on or off, it does not work. And then suddenly, out of the blue it starts working again. If it works during daylight, it will start to heat the water properly. Sometimes it works at night and clearly doesn’t heat water.

When it is dead there doesn’t seem to be anything I can do to make it work again. Has anybody got any ideas? Thank you