I replaced mine because the pilot light wouldnt stay lit.Last time I bought one of these was 2 consecutive years ago. At that time, I bought 2. Because before that, thermocouple with block only lasted a year and some months.At that time, I was paying $26.00 for each Williams thermocouple with junction box/block(which was higher than thermocouples without junction boxes). But look at current price for Williams 322391. Thanks goodness I bought two of these, two years ago. Now, you might as well invest in a new heater (if you are coming out the pockets) than spend almost $100 on 1 minor replacement part that will not stay lit no more than 2 years.One way to keep your new Williams 322391 thermocouple working for up to two years (because it wont last longer than that) is to remove it and clean the tip with a steel brush after each winter. Otherwise, it wont last that long.Replacement is easy. You can do it yourself. Watch youtube video by searching: "williams wall heater thermocouple replacement "