Nest Thermostat No Power to Rh Wire – Nest e74 Error

A lot of appliances in your house are liable to show you errors. Especially those concerning your lifestyle. Speaking of your gadgets such as your laptop and your smartphone, you can easily diagnose the problems with these devices unless the problem is pretty technical. What we are going to talk to you about today isn’t your usual refrigerator or even television for that matter.

What we have for today is a thermostat which is integrated into your house’s HVAC system and it isn’t just any thermostat, it is the Nest thermostat which has gotten quite brilliant reviews by those who have installed it in their home and have used it. We won’t be talking about all of that today because our topic of concern is an error that shows up on the Nest thermostat.

This error is known as the Nest E74 error which is basically the code for when your Nest thermostat isn’t being provided power by the Rh Wire it is connected to. Since it isn’t being provided with power then the thermostat won’t be able to charge properly and when your HVAC system fails to work, it won’t be able to provide the required backup.

If you have a Nest 74 Error in your thermostat then you’ve come to the right place because we are going to be discussing the solution of your problem by which this issue can be fixed. Make sure not to panic because your thermostat isn’t broken. There are a few inconveniences that might have caused this error and with our proposed solutions they’ll be going away.

Let us now begin discussing the solutions that can take you out of this mess.

Solutions to solve Nest Thermostat No Power to Rh Wire – Nest e74 Error

Check Rh Wire Connection

Whenever you come across a Nest E74 error then the first method by which you should troubleshoot this is by checking the wire of the thermostat. In fact, the most common problem that leads to the Nest E74 error is this. This is because the Rh Wire connection is termed as E74 in code.

This error tells you that the power to the Rh wire isn’t being supplied correctly which is why the thermostat is having issues in getting power. There is a big chance your power will be lost whenever your thermostat loses connection. This could lead to an even bigger problem where the unavailability of power would lead to your thermostat not being charged.

You can also view the Tech Info Diagram of your thermostat to view the main connection of the diagram of your thermostat. The main purpose of this diagram is to highlight the important connections of the thermostat and usually the Rh wire is loose and red in color. Make sure to keep this hint in mind if your Rh wire is disconnected and you need to connect it back.

If our Rh wire is shown as a red connection then all you need to do is remove the display and check for this wire. You will need to insert this wire properly and fix it in place. This thermostat won’t be able to function the right way if the wire is loose. The thermostat won’t establish a proper connection either if damages to the wire are seen.

HVAC Float Switch

The HVAC system of your thermostat has an overflow switch as well. This particular switch is located near its Air Handler unit. This switch has been integrated into your thermostat to prevent water overflowing from your entire house.

For any unknown reason the water in your drainage pipe isn’t flowing properly or whether if it’s clogged then the condensate switch is going to disconnect and this will stop power to your AC. After making sure the Rh wire is working properly, check and see if your condensate switch is working.

This switch has a floating mechanism in place. This switch disconnects the internal switch as it floats to the top after coming into contact with water. To check whether the switch is working or not, shake the switch with a little force. If the switch makes a click sound then the switch is in its right place.

However, if the switch is somehow disconnected then there is going to be water in the overflow switch and the clicking sound will not be heard then. You will then need to clean your drainage pipes and move the float towards the bottom part of the thermostat.

Charge Thermostat Using USB

The final thing that you could do as a fix for this issue is to charge your thermostat using a USB connection. Follow these steps to charge it using your USB:

  • Remove your thermostat from the wall plate

  • At the back of it you’ll see two connectors

  • One of them will be a MicroUSB 2.0 port

  • Connect the Nest using a compatible charger and let your thermostat charge for an hour

  • While charging, your display will boot automatically in a couple of minutes

Control Unit Fuse of HVAC

Many times due to improper connections or power fluctuations showing up, the HVAC system of your thermostat has a control unit fuse. This fuse can very easily blow up often. The HVAC System of your thermostat has a control unit fuse that can blow up due to power fluctuations or due to loose connections. This fuse is attached to your HVAC’s control unit. This tiny switch is present on the bottom right side of your unit.

To check for a blown fuse, use the steps given:

  • First turn off your HVAC System
  • Remove the fuse
  • Check to see if the connection at the center is broken or not. The control unit fuse has a transparent casing hence the wires shall be visible to you
  • Check for a white, u-shaped wire
  • If this wire is broken or damaged in any way then the fuse if probably blown

If you’re planning to get a new fuse for yourself then make sure to get it for the same color which you blew the fuse up for because having the same colors will have the same fuse rating. This color coding in terms of fuses is important.

Apart from this, if you have a blown fuse then there is a good chance that your Nest thermometer might have any other ongoing issue which might have caused the Nest N74 error. If this method doesn’t seem to work then you can move on to the next one.


The Nest E74 error can be a real headache for you since you don’t know what might’ve caused the issue. Gladly the methods we’ve brought for you are going to be of immense help for you because they are going to help you work your way around this problem.

Hopefully either one of the methods that we’ve mentioned above is going to fix this problem for you because we don’t want you having a broken thermostat in your house and you not being able to fix it!