I recently moved into a house with forced air oil heating, and I wanted to use my Nest Generation 3 with it. There were only two wires running to the old thermostat (which used AA batteries): red and white (RH and W, with a jumper between RH and RC). I connected RH and W to the Nest, without the jumper (according to Nest's instructions).
After hooking it up, the Nest gave me Low Battery errors (wouldn't connect to Wi-Fi, Nest App not working). The Nest hadn't been used for awhile, so I pulled it off the wall, recharged it using a USB cable, and connected it back up. It worked fine for about a day, then it showed Low Battery errors again. The thermostat is still turning heat on/off, but the battery isn't charging, and the App and Wi-Fi won't work.
After some digging, it appears I'd need to get a Nest Power Connector (in lieu of having a C wire pulled). This is fine - but there's no terminal labeled C on the controller: a Honeywell R7284.
This thread: https://diy.stackexchange.com/questions/241814/is-it-possible-to-add-a-c-wire-to-a-honeywell-r7284-o... and the manual it refers to: https://jacksonsystems.com/wp-content/uploads/2020/04/R7284-Installation-Manual.pdf seem to show that terminal 2 is the same as C. But there was no follow-up confirming if this worked or not. According to the manual the voltage across 2 and 3 should be ~24VAC. Mine reads 28VAC. What I don't know - is what the Nest Power Connector is expecting, and if it's safe for the Honeywell controller and Nest equipment to connect it this way.
The only thread I've found in this Community with a similar controller: https://www.googlenestcommunity.com/t5/Nest-Thermostats/Nest-Thermostat-C-Connector-with-Oil-burner-... isn't applicable, since we don't have the fan control relay, AC unit, etc.
I'd appreciate any help on the subject. If I can safely use terminal 2 as C - great! If I need to call in an HVAC technician - happy to do so. Thank you!
- Nathan
