Fuse board fault finding - Heat pump

I received a call that the pump fuse board had been tripping the electrics

I took the cover off the board after making myself comfy.

1. Remove cover
2. Split all neutrals at the neutral bar
3. Test between Live and earth at 250V, each circuit, circuit 3 showed a reading of 1.40M ohms, I thought this was the fault. This was on a 16 amp mcb. This was the summer house. I went to this, turned the rotary isolator off, tested the cabling between the pool pump and here, and it showed 999M ohms. When plugging in a polarity tester with isolator on and circuit reconnected, it tripped the RCD at the pool fuse board every time ???
4. I assumed it was the garden summer room ..
5. I had not tested the earth to neutral on each circuit
6. I re-tested each circuit neutral to earth and found the heat pump to have a dead short between earth and neutral, reading 0.03 M ohms, which backfed a fault between live and earth on the summer house circuit.
7. The neutral was left disconnected on the heat pump circuit, and all other neutrals were reinstalled.
8. The power was restored to all other circuits and the Heat pump was disconnected, upon inspection the heatpump has been overgrown by foliage and most likley the heat pump has had slugs/snails crawling within it, as it was a 10 year old item I suggested contacting supplier/installer to arrange a replacement as the tech changes every 1-2 years at the current rate and spares would be impossible to find for a 10 year old heat pump
9. Power restored - client happy