Note I'm only talking about the neutral line coming from the spa.

The copper is supposed to be ground, in most cases attached to the neutral/ground bus-bar.

Ok, changed the wires as directed now GFCI fails to set at all - obviously a problem with the initial wiring as my main spa box has a stove connector and I didn't have this plugged in at the time.

The set up my friend wired is as follows:

spa main box plugs into stove receptacle 4 wire (red, black, blue and copper). This then leads to the wall kill switch (probably not the right terminology - forgive me I'm British from there to inside the house - junction box that connects external to internal wire - internal wire to main panel.

I know this is really tedious for you but if I can sort this I'll be a happy man (not to mention how excited my girlfriend will be)

Well this is a little kooky.

I've never worked on a canadian system.

I know the physics are the same, but you're referring to blue wires which I'm assuming for the moment is neutral... however that doesn't mean that my assumption is correct.

You'll need to verify everything from the main box all the way to the spa.

The out going neutral line from the ground fault circuit breaker should never be wired or attached to ground anywhere. I'm guessing that it may be most likely that your neutral line is not isolated properly, that means all the way to the tub control box.

Which is why I suspect initially that the gfi trips when anything that runs primarily on 115 volts is turned on, including the topside control.

You need to verify everything is correct before going to work on the controller. Photos of everything start to finish will help that, and, without something like this to justify any further troubleshooting, nobody will be able to help you with this.

You're an absolute genius, you nailed the problem on the head - I checked the kill switch and the neutral had been wired where the ground should have been - changed it over and all looks good.
Both myself and my girlfriend are very very grateful

Well that's good.

At least something's working today...

Can you believe I'm back so soon
So, the tub is running, jets, light command panel - but no heat.
The heat light shows up on the command center but is off on the main box. I've also felt the tubed area where the heater element is - nothing
Any ideas
oh, one of the new bits this year was the heater element

That doesn't really mean the heater is not working. Those indicator bulbs are usually neon and do wear out.

You won't be able to feel heat at the heater. It's not a lot of power going into the element anyway...

If you rotate the temp knob low to high can you hear the contactor 'click' on and off?

Unfortunately no clicking

Try it on high speed to see if that will kick it on.

If so, then suspect your pressure switch needing adjustment.

If not, then suspect that it may be that something is amiss from you replacing everything

You are getting good water pressure right?

And check that switch setting on the front panel.

When I move the temp switch on the command center I hear a quiet click from there but nothing from the main box. By high speed do you mean pressing the jets button. I think I'm getting good pressure, the jets really kick out when i turn them on. And you mention check the switch on the front panel, which one (now you can see I'm really new at this
Roughly what should my pressure switch be set at (tight / loose)