Home Improvement Questions? Ask a Handyman for Answers
Most likely it is the mercury switch that has been bypassed. These are a known weak point on this model. The availability of this switch is very limited and they are fairly expensive. I think around 200 dollars for the part. Repairing this fireplace will probably cost around 350-500 for parts and labor. As far as replacing the whole unit, that can range anywhere from 1000 on the low side up to 5000 depending on the unit purchased, the chimney configuration, and how much of the decorative tile and surround is to be replaced.
Hopefully this helps,