cancel
Showing results for 
Search instead for 
Did you mean: 

E448: No system power, on Nest Thermostat 4th Generation.

yoummr
Community Member

 

I recently purchased the 4th generation Nest thermostat, but it occasionally displays an error message for about 2 to 10 minutes. While this doesn't bother me too much since the heat eventually runs again, even if I'm away from home, it does happen sporadically—sometimes daily or weekly—even after recharging and removing the thermostat.

The main issue is that sometimes the system does not start, even when the thermostat is set to a high temperature. Although the thermostat remains powered on, the Vin reading drops to just 6.4V. The system only works again after removing and reconnecting the thermostat.

Questions:

  1. Why is this happening?
  2. How can I fix it?
  3. Will it damage my boiler or HVAC power system?
  4. Can I use the C-power adapter and connect from the outlet rather than the Nest connector? 
  5. What will be the guaranteed solution I do not want to expend a lot of money. 

System Details:

  • Boiler: Water steam heater with radiators powered by gas (blue color). - heat only
  • Wiring: Two wires connected — White (W1) and Red (Rh).
  • Vin (Thermostat Device Info): 6.4V or lower.

20250107_114613.jpg

 


  
Screenshot_20250109_135648_Home.jpg

5cbe45d8-cfea-4069-bf08-a46dd6ad5fb1.jpg20250110_120102 (2).jpg

2 Recommended AnswerS

sdworman
Community Member

A Nest power connector would be the better option as long as you have a circuit board on the furnace.  Ma t times a heat only system will not have a circuit board.

 

A 24 volt transformer at the furnace connected on the Rh at the thermostat doesn't provide the constant power needed to keep the Nest on and connected to WiFi.  Adding the "C" wire either with a 24 volt plug in transformer or the Nest Power Connector accomplish this.

 

View Recommended Answer in original post

Patrick_Caezza
Diamond Product Expert
Diamond Product Expert

@yoummr 

If you use the Power Connector you will need both.

If you don't mind having a cable going to a wall transformer at the thermostat location, you can connect the external transformer to the Rh and C terminals on the nest.

I prefer not to have a cable at the thermostat.

 

 


To ensure that I see your reply, please tag me using @Patrick_Caezza

View Recommended Answer in original post

8 REPLIES 8

moralesvicente
Community Specialist
Community Specialist

Hi yoummr, 

 

Thank you so much for posting in the Google Nest Community forum. I’m sorry to know that your Nest Learning Thermostat 4th generation is showing an error code E448. Don’t worry; I’m here to assist you. 

I appreciate the information provided. Based on the error code displayed on your thermostat, it means that there's no power in your system; therefore, I suggest checking these steps. 

  • Ensure that the wiring system is connected properly in each terminal.

  • Make sure your power source is sending energy to your thermostat. 

  • Your thermostat might need extra power. You can usually fix this by installing a C-wire or using the Nest Power Connector connected directly to the baseboard of your HVAC system.

To learn more information regarding this situation, check out this article: Troubleshoot Nest thermostat help codes

I'll look forward to your response.

 

Best regards,

Daniel 

I have a customer with this same issue.  The Nest Power Connector solution will not work in a heat only 2 wire scenario.  Also it will not work well without a circuit board and would require an electrician to hard wire this power connector.

The Nest gets power, connects, then the Nest complains about no power.  So, I agree it needs more power.  The ideal solution is a 24 Volt transformer pugged into the wall outlet by the t-stat.  Connect one line to the Rh and the other line to the C for the common wire.  This all sounds good in theory, and since Nest does not make this, will it work?  Otherwise in all scenarios, since all models of the Nest we tried without a "C" wire will require the "c" wire.  The house was built in 1920.

yoummr
Community Member

@sdworman 
**** Re: The main issue is that sometimes the system does not start, even when the thermostat is set to a high temperature. Although the thermostat remains powered on with a Vin reading of only 6.4V, the system only starts working again if the thermostat is removed and reconnected.
  

I would like to install a 24-volt transformer (which I purchased from Amazon) to power my Nest thermostat.
Does Nest recommend this solution? I want to avoid any risk of damaging my system, as there would be power coming from both the Rh terminal from the HVAC system and the plugged-in transformer.

Alternatively, would installing a Nest Power Connector in the HVAC system be a guaranteed solution to this issue?

sdworman
Community Member

A Nest power connector would be the better option as long as you have a circuit board on the furnace.  Ma t times a heat only system will not have a circuit board.

 

A 24 volt transformer at the furnace connected on the Rh at the thermostat doesn't provide the constant power needed to keep the Nest on and connected to WiFi.  Adding the "C" wire either with a 24 volt plug in transformer or the Nest Power Connector accomplish this.

 

Patrick_Caezza
Diamond Product Expert
Diamond Product Expert

@yoummr 

With a 2-wire heat-only system you need to install the Google Nest Power Connector and an external 24vac transformer.

Follow these instructions,

You want to connect the red wire to the Rh terminal and the white wire to the W1 terminal.

2022-03-01_173137.jpg2022-04-06_182952.jpg


To ensure that I see your reply, please tag me using @Patrick_Caezza

@Patrick_Caezza 
Thanks a lot , Do I need both Google Nest Power Connector and an external 24vac transformer?
Or one of them is ok? 


Patrick_Caezza
Diamond Product Expert
Diamond Product Expert

@yoummr 

If you use the Power Connector you will need both.

If you don't mind having a cable going to a wall transformer at the thermostat location, you can connect the external transformer to the Rh and C terminals on the nest.

I prefer not to have a cable at the thermostat.

 

 


To ensure that I see your reply, please tag me using @Patrick_Caezza

@Patrick_Caezza 

"I've installed an AC 24V Transformer (C-Wire Adapter) by connecting one wire to the C terminal and the other to Rc. Previously, I connected the white wire from the boiler to W1 and the red wire from the boiler to Rc. Everything seems to be working fine so far."

Let me know if you'd like any further refinements!