I have a hot springs prodigy spa 110v - I believe it's 1990. After draining and refilling i plugged in the spa and it began to spark where the heater plugs into the box (receptacle). I unplugged the spa and saw that the heater plut and the J &J recepticle had melted. I unplugged the heater from the control box and everything else seems to be working fine. I took to box out to see if anything inside had melted but everything looks okay.
Inside are 3 relays marked 1,2,3. The heater is number 3. The contacts on this seem a little more worn and pitted than the other two and are blackish compared to the others which are white. Any ideas what might have happened here? I just acquired a used heater and new recepticle. Should I just replace and go or could this be the relay's fault?
I can post photos if that would help.

To find the year - look in the equipment area for a sticker with a number that starts with an H. H102561 would be a 1st quarter 1990 Prodigy. The 1st number being the quarter with the 2nd number being the year.
A power surge could cause that to happen. It's not uncommon to see it. I would replace the heater relay just in case - part #70297.

Pete

i did notice this morning on the two bare copper wires that run into the box (with the probes on the ends) one might have been touching the box as the little plastic that surrounds the hole where it enters the box was cracked. Could this have caused the burn and if so - what can I do to fix this. I havent' found anyplace that sells the plastic that guards the little holes in the box.

I don't think that had anything to do with it. You can tape the probe at the box with electrical tape. Be careful with those probes - do not kink the tube.

Pete