It would help if we knew what style of heater you were previously using, as in... was it a stainless steel tube? Plastic housing with an L shaped design? You can get a digital thermostat all alone, but considering the age of the tub, you'd be much better off with a new pack. It's less than 100.00 difference between replacing a heater assembly complete with a topside digital thermostat, and getting an entirely new set of innards for the spa, and you'll have everything you want with it... It'll give new life for the thing.
I'm going to take a stab in the dark on this... if yours has a Brett style heater, the complete replacement is 276. A digital topside to work with this would be 142. You're up to $418 not including shipping.... and then there's the work you have to do to get it back running again, and you've still got an old control system.
A Smart Touch Digital 1000 is $495 and comes with all the cords you need. You'll just have to get it plumbed in. But when you're finished, you've got a completely new and up to date digital control system, with a heater.
http://spapartsnet.com/products/SPDACCD1.html
Hope this helps!
To top it off, the amount of work in getting it fixed may actually be less with installing a new spa pack with a digital topside, as opposed to having to replumb, and rewire and install a new heater.
