How to Fix No Power to RH Wire on Nest Thermostat? (6 Ways)

Not sure why you just received an e74 message on your screen? This warning message indicates that your Ph wire is not receiving sufficient power to function. However, you don’t have to worry about it as you can easily fix this error without spending hundreds of dollars.

So, how to fix the nest e74 error?

To fix the e74 error, check your Rh wire’s connection and ensure it’s fine. Check the HVAC float switch and HVAC control unit fuse if that doesn’t work. However, if that also doesn’t go well for you, replace the HVAC contractor replay.

So, keep reading to know in detail about all the hacks you may opt to fix the nest e74 error.

How to Fix No Power to Rh Wire on Nest Thermostat?

How to fix Nest no power to Rh wire problem?

To fix the error e74 no power to Rh wire, you just need to follow some troubleshooting steps. These are pretty easy to follow and would save you hundreds of dollars you would spend at the repair shop.

Below are the fixes for Nest no power to Rh wire problem:

1. Try checking the Rh wire connection

The first step to fix the nest error e74 is to ensure all the connections of your Nest thermostat are fine and there is no interruption in them. The main connection includes that of Rh wire.

Therefore, when you get the error, simply head to the connection diagram and check if the display indicates a missing Rh wire. For example, you may see a red indicator because of no power supply to the Rh wire.

After checking the display part, take it off and inspect the Rh wire. Ensure the connection is well and tight enough to prevent any disruption. If not, then fix it accordingly. However, if it doesn’t help you in fixing the e74 error, head to the next hack.

2. Try checking the HVAC float switch

The next hack is to check the HVAC float switch and ensure it works well. The float switch is an essential part of the HVAC system near the Air Handler unit. It ensures that the water flows properly through the drainage pipe, thus preventing your home from over flooding.

However, due to any blockage within the drainage pipes, the water may not flow properly and, therefore, may disconnect your condensate switch by the floating mechanism. According to this mechanism, the switch may float in the water and then disconnect itself. This will then directly disrupt the power to your AC.

So, after checking the connection of your Rh wire, it is essential to ensure the proper working of the float switch. Next, you just need to move the float back and forth, which may produce a tiny clicking sound. This sound indicates that your switch is working well.

Below are the steps to make your float switch work effectively:

  1. Clean the drainage pipe and remove any clogging material in it.
  2. Next, move the float to the bottom.
  3. Lastly, wait for a few seconds and then check the status of the RH wire on the Nest display.

3. Try checking the HVAC control unit fuse

If adjusting the float switch didn’t fix any power problem, then the next step is to check the HVAC control unit fuse. The fuse may blow up when there is power fluctuation in the system.

To check the functionality of the HVAC control unit fuse, you need to run a small test which is as follows:

  1. Firstly, turn off the power to the HVAC system.
  2. Next, remove the fuse, check the connection center, and ensure there is no damaged or waterlogged equipment within.
  3. If you see a broken U shape wire, this shows a blown-up fuse; thus, you need to change the entire HVAC control unit.

This process may be a bit technical. Therefore, we recommend you call an expert for better results.

4. Try replacing the HVAC contractor relay

The next hack is to replace the HVAC contractor relay in the outdoor AC unit if it has any damage. Your relay may show errors due to aging. However, its other causes are not known.

Sometimes it may even produce sparks while the coil may also blow out from the control unit. You may need to change the fuse and the relay in such a situation. Therefore, we recommend you seek help from an expert in this concern to avoid any mishap.

5. Try charging the Nest thermostat manually

If you don’t get an efficient result by replacing the HVAC contractor relay, try charging the Nest thermostat using a USB-enabled device or manually. This hack may go really well for you when your Nest doesn’t receive its power for more than 12 hours, and there are no indications for other errors.

So, you just need to plug your Nest device into the USB-enabled device and make sure it charges it up. However, if your device remains blank with no effective results, opt for manual charging.

Here are the steps to charge your Nest thermostat manually:

  1. Firstly, remove the thermostat from the wall.
  2. Next, find the micro USB port by looking at the two connectors on the back panel.
  3. Connect the thermostat to the port.
  4. Lastly, leave it for a few hours until the battery gets fully charged.

Read more: Difference between Nest protect battery and wired

6. Try using a Shop VAC on the drain lines

Last but not least, if you find your drains clogged up during the troubleshooting hacks, you may simply clean them up without seeking any expert’s help.

So, simply head outside and use a vacuum to remove all the dirt from the drain lines’ valve. Moreover, you may use a Shop Vac to exert extra force on the drain lines. This will make the process more successful.

We recommend you clean the drains every few months to avoid such a situation.


What do RC and Rh mean on the thermostat?

The Rc terminal on the thermostat is the 24 Volt cooling power supply. In comparison, the Rh terminal is the 24 Volt heating power supply. These terminals are joined in a four-wire heat/cool system and a single-stage pump system and not a five-wire heat/cool system.

What is the RH wire on a thermostat?

The Rh wire indicates the Red heating, which directs towards the connection to the power for the heating system of your AC. If this connection is unavailable, the air conditioning may stop working.

Similar Articles

  1. What does nest error E195 mean
  2. How to fix the Nest not turning on AC
  3. What causes Nest thermostat not turning on heat
  4. What causes the Nest thermostat not to cool


The Nest thermostat has no power to Rh wire, or the nest e74 error may be due to several issues, most commonly due to connection errors. Other important causes may include a defect in the HVAC float switch and HVAC control unit switch. All these causes are reversible and may easily be removed without support.

So, in this blog, we have written all the possible hacks to fix e74 error. They’re pretty easy to follow and will help you save hundreds of dollars you may need to spend at the repair shop.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top