Hello DIY forum! I was hoping to get some help with an issue I've been having in replacing my old Honeywell mercury switch thermostats with smart thermostats (ecobee3 lites) set up in our dual transformer (forced air AC + boiler/zone valve hydronic baseboards). Both thermostats, which are on separate zones for both AC (separate air handlers and condensers) and for heat (separate zone valves), have failed. They fail on the heat side leading to what appears to be a short circuit leading to a constant call for heat no matter what the setting on the thermostat. Removing the t'stat stops the call for heat, and ecobee had been very helpful in getting the units replaced (still awaiting 1 of the 2 replacements) and setting up a 2nd stage heating workaround (using W2 instead of W1 terminal) to get the t'stats working in the meantime. In the meantime, both ecobees have now failed on the W2 as well. This leads me to believe that this was not lightning striking twice, but rather there's some wiring/system issue in our house frying these poor ecobees! Before I go and kill my warranty replacement t'stats, I wanted to try and get some insight here on what I might be able to do to ensure I don't have issues with the new ones. For reference, here are pictures of my first floor thermostat wiring: [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1124/them_1158d4529d75f2e73067034e62f4c513ab3888c9.jpg[/img] First floor air handler wiring (note I had connected an unused blue wire to the c-terminal here for this t'stat): [img]https://cimg7.ibsrv.net/gimg/www.doityourselft.com-vbulletin/2000x1504/ah2_bdcb73aef1038dd6e67cccb0156147b401e79f9e.jpg[/img] Zone valve wiring (annotated): [img]https://cimg4.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1197x768/zv_a90b8f619fee20cd6f34eaff7e3c2567cd45dbbd.png[/img] [img]https://cimg6.ibsrv.net/gimg/www.doityourselft.com-vbulletin/815x807/transf_230b56f0d8a2fe5d8860491ea9290cd8ccba05e8.png[/img] [b]I have been running around with a multimeter trying to get some insight and have some thoughts on what may be causing the issue:[/b][indent=40px]1. I am reading ~24v between my Rc and Rh (and therefore the thermostat is potentially exposed to 48v e.g. from Rc to W). Could this be frying the t'stat? Is this a phase issue? 2. Compared to some wiring diagrams I've seen on the internet, the heating side transformer appears to be wired backwards (with Load wired to zone valve terminal #2 and C wired to thermostat Rh wires) 3. I have no isolation relays installed and have seen some mention on the internet of using them with hydronic + smart thermostats... [/indent][b]Very curious if one of the three issues above (or another issue!) could be frying these ecobees. Any help is much appreciated!![/b]

Hi, I know people of already posted threads regarding the U1 wiring but I guess the wiring internally in the attic may differ on case by case basis. So here I am presenting my case and looking for answers from the pros. I've read the U1 could be connected to the humidifier/dehumidifier but it doesn't look like to me what i saw in the attic (I could be wrong). Below are the pictures I've gathered. Please let me know what needs to be done? Thank you, Siphons [img]https://cimg2.ibsrv.net/gimg/www.doityourselft.com-vbulletin/740x829/1_2d5dcc4e641da238b9bedc86e226502f5f976033.jpg[/img] [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/738x710/2_c1b5d428fb2fbc0db318f3692381a0ce017e1563.jpg[/img] [img]https://cimg4.ibsrv.net/gimg/www.doityourselft.com-vbulletin/739x986/3_6acbda45bdad93758073a5acde632e160c78ae5b.jpg[/img] [img]https://cimg4.ibsrv.net/gimg/www.doityourselft.com-vbulletin/747x719/4_23d236a35f288c76e187bbf1ca097dfef8dadbc9.jpg[/img] [img]https://cimg5.ibsrv.net/gimg/www.doityourselft.com-vbulletin/1500x2000/honeywell_u1_wiring_c7e1b4580f46cadd3ba899b296bbf5f089a9ee03.jpeg[/img]