Nest Displaying "No Power To Rc Wire" Error? (Possible Causes & Fixes)

Nest has several error codes that may appear on the screen to let you know something is amiss. While it can be alarming, there are usually plenty of ways to troubleshoot the problems yourself.

You may be prompted to look at the screen if your Nest starts acting up for unknown reasons. If you receive an E73 error message on your Nest, it means there’s no power to the Rc wire.

The “No power to Rc wire” message is commonly due to incorrect or loose wiring. Before checking the wiring, first, make sure the HVAC breaker hasn’t tripped. Other reasons for the message include a clogged air filter or excess water build-up in your AC drip pan. Finally, the fuse on your furnace may have blown.

You may have noticed a lot of power issues associated with your Nest after receiving this E73 message. It’s partially correct to assume, then, that the Rc wire gives power to the thermostat. It could be a bit more complicated than that, though.

You could have either an Rc or an Rh wire. Regardless of which one you have, if there’s only one, it powers the entire HVAC system—heat as well as air.

But your Nest has two terminals: Rh and Rc. So where do you put the wire? If you only have one R wire, you can put it in either terminal. Nest has both of these terminals because of how some HVAC systems are designed.

Some HVAC systems, known as dual transfer systems, use separate power for heating and cooling. In this case, you’ll have both an Rh and an Rc wire. The Rh wire powers the heat and the Rc wire powers the air.

Note: If you have a dual transfer system, Google recommends contacting a professional to install or troubleshoot your Nest. A professional can navigate the complicated system to avoid damage.

The most obvious reason your system isn’t receiving power is that the power is off! Even if the power to your HVAC system is off, Nest may still work intermittently because of its internal battery. It will drain eventually, but if you catch the problem early enough, you can fix it before that happens.

The first place to look is your breaker panel or fuse box. You may have a single switch or two separate switches—one for heating and one for cooling. Make sure both are in the “On” position.

In some homes, the power for the HVAC system is actually located right next to it. It may look like a light switch. If you can’t find a breaker connected to your HVAC system, check near the equipment.

If the breaker was tripped, flip it back on and see if power has returned to your Nest.

Related Questions

Is an Rc wire the same as a C wire?

No. In the case of only one R cable, the Rc wire powers the heating and cooling system. If you have an Rh and an Rc wire, the Rc wire powers the air conditioner. The C wire provides power to the thermostat.Nest maintains that you don’t need a C wire for the thermostat to run. This is true. But you need a C wire for the thermostat to run properly. Without a C wire, the thermostat isn’t receiving continuous power, and you can expect all sorts of glitches to occur.

What happens if Nest thermostat loses power?

Because of its internal battery, Nest will run for a time during a power outage. It relies on the charge that was created while the power was running. The battery usually lasts an additional 1-2 hours. Once the battery drains, the Nest loses power as well. All of your programs should be maintained when the power returns.

An E73 error means there’s no power going to your Nest’s Rc wire. This can affect the function of your air conditioner, the Nest’s power, or both.

The most common reason to receive an E73 message is due to improper or loose wiring. To avoid this issue, it might be best to have a professional install your Nest in the first place.

If the wiring isn’t to blame, the problem lies with your air conditioner. It could be a clogged air filter, full drip pan, or blown fuse. Don’t be afraid to contact a professional if you have any concerns.