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Nests - Error E74

Monitorjak Member Posts: 1

I have 2 nests installed for different heat pump units. (1 for each unit) and I'm having the same issue with both.
I have the following connected Y1, W1, G, O/B, C, and RH.
It doesn't seem to accept the RH on either. I've used a multimeter and only recorded voltage on the C wire on 1.
The other I only recorded voltage on the RH wire and this one constantly runs the heat out of control. Came home to 100+ temperature Fahrenheit.
Both worked fine for about 5 months. Then my heat pump crashed (27 year old system) shortly after having it replaced the Nest connected stopped working due to no battery charge and my other Nest went crazy.
I have the breaker flipped off for both.
Help Please!


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,506
    edited April 2017
    I assume you went to their website for some troubleshooting:
    Few options:
    -Check all the wires and their connections making sure they are properly secure at the Nest and on the unit.
    -Check continuity of all wires from Nest to unit-power off.
    -Remove C wire, nut it off so it doesn't touch any other wires, flip breaker back on.
    -Remove Nest, try charging it with usb cable on computer.
    ~~and finally~~
    Throw nest in trash and get a Honeywell Lyric
  • iix
    iix Member Posts: 18
    I'd do the above and also move that wire from Rh to Rc too some of the smart stats have some strange quirks when it comes to power.