Think of a fuse like a light bulb. The Filament is very fragile and will blow over the slightest anomoly ( could be a million differnt things ). Once a fuse is blown, no power will go to the unit. If there was no apparent cause, I wouldn't dwell on it too much. Being a Electrician, and having delt with some very sensitive Electronics, I've seen it happen time and time again. Some fuses last forever, some don't; Again, think about a light bulb. You might want to look on your owners manual or contact Jeff Washburn about using Helix's with surge protectors. I believe that they suggest not using a surge protector because the unit is already surge protected and may cause potential damage to the unit ( can't remember the specifics ). I used to use Helix's, but after 10-12 months of use they would show an E3 error and I would have to send them back to Helix to get them reset. I've been using Ranco's since and never had any problems. Where I live we have alot of power outages, and that seems to tear up proportional thermostats for whatever reason

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