Receiving “rH wire no power” & e4 message

[Chez_Topaz]

12 year old Nest is not charging. When power is cycled to the furnace - only the fan runs.

Steps to date:

1) charged the display

2) changed filters

3) reset the unit

4) cycled furnace circuit

result: no rH power detected “e4” code

[Houptee]

There might be a blown fuse on the board in the furnace or the transformer is bad or a wire is broken somewhere.

You would need a multimeter to test for 24v AC voltage at the furnace. Put the meter in AC voltage test mode and put red test probe on R screw and black probe on C screw and test for 24v AC.

If no voltage at the system terminals look for the fuse see if its blown they usually look like car fuses or could be a glass fuse.

https://support.google.com/googlenest/answer/9235307#zippy=%2Ccheck-the-hvac-fuse

[Markjosephp]

Hello folks,

I wanted to stop by and see how I could help.

Thanks for your expertise here, @Houptee.

@Chez_Topaz, your thermostat may not receive enough power or any power at all from your system, which would prevent it from completing a circuit and causing a report to be shown. You can also check your thermostat's power readouts under "Technical Info," and you should get at least 24V on Voc and Vin. if below the required voltage. Remove the C wire and leave it disconnected if you have, then check the power readouts again and see if there are any changes. If so, the common wire may not be properly grounded, so the system uses power sharing but doesn’t get enough energy.

Please let us know on how it goes.

Regards,
 Mark

[Markjosephp]

Hi Chez_Topaz,

I wanted to see if you still needed help. Please let us know if you have any other questions or concerns.

Thanks,

Mark

[Markjosephp]

Hello Chez_Topaz,

I'm checking in to make sure that you've seen our response. Please let us know if you have any additional questions or concerns before we lock this thread in 24 hours. 

Thanks,

Mark