Hard to believe your pool company can't at least give yousome idea of the problem. How old is your heater? If it's newer say under 5 years old it's probably still under a warranty. If it's less than 10 might still be worth fixing. Did they say anything about the heat exchanger being bad? If so then a new unit is likley needed.

FYI my company told me the same thing and in the end they were right - I made them tryto fix my 7 yr old Raypak unit and it was too rusted out.

Good luck
-Craig