I had a Hydroforce submersible pump Series 3 pump replaced under guarantee after about 18 months. About 3 years on I have a renewed intermittent tripping problem. It is protected by a 30mA RCD ELCB. I suspect the problem is in the pump.
A few recommendations:
1) Avoid external connection box – always bring the flex indoors. Exterior connections even in an IP66 box risk condensation and at best, complicate fault-finding.
2) Connect via a time-switch. Two 10 minute pumps a day are better than say 30 1 minute pumps as:
quieter, less energy use, possibly less wear, precludes possibility of pressure switch cycling if any pipe joints are weeping.
3) Consider installing via a separate dedicated RCD ELCB to facilitate use of a less sensitive trip e.g. 100mA or 300mA, (if allowed – seek professional advice). Any tripping will then only affect the pump.
These are my own views, i.e. those of an unqualified but informed self-builder. I have not checked them against Hydroforce installation advice.