Quote Originally Posted by Servicetech View Post
Keep in mind the condenser of a heat pump system will send voltage on the W terminal during defrost cycles. This may be what is killing the Nest FET's
Could be, but in my case a series of events capped off by inattentiveness by my heat pump installer has resulted in my defrost control line being connected to a relay that is not connected to the thermostat. My aux heat control at the thermostat is only connected to the other heat strip. So if the defrost control is frying things, it has to be via cross talk. I currently have an 11.3 kw heat strip that is only ever on during defrost and a 7.7 kw heat strip serving as aux heat. I'm currently working on fixing things so I can have the 11.3 kw available for emergency heat. My compressor is LOUD (82 dB at 3 feet). American Standard says that as long as it makes pressure tests, it isn't their problem. I figure anything that loud is going to fail early. I need to be prepared to heat the house without the compressor. The compressor has lasted 8 years, but it's getting much louder.

I figure I'll buy a Prestige 2 (I have 10 conductors to the thermostat, so why bother with an EIM) when my Nest refund finally arrives. I'm on week 8 since Nest took possession of my third fried puck. The Prestige 2 is supposed to be able to handle a second backup heat strip via the universal contacts. I could live with my 2005 vintage American Standard badged Honeywell, since it's emergency heat terminal would, according to the manual, handle a second heat strip in place of the compressor while leaving the existing aux heat as aux heat during eheat time. But I would like a way to access the temperature setting while on the road. Despite the added cost for the Honeywell communication capabilities, I think I'll eventually be happier with Redlink than wifi that gets to be a legacy hassle at my router.

I've been unhappy with Honeywell in the past for some of their design decisions, and for their unwillingness to deal at all with the likes of me (not employed in the HVAC industry). But after the Nest fiasco, I've come to better appreciate some of Honeywell's strengths.