Why does my thermostat keep losing power and resetting?
A short in the 24V circuit or a failing HVAC transformer often causes the furnace control board to lose power, which trips the 3-amp safety device and kills the thermostat. This leaves the system completely dead or causes smart thermostats like the Nest and Ecobee to repeatedly reboot during a call for heat.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Resetting the 3AMP device/fuseDid this help you?
- 2Removing wires one at a time to check for shortsDid this help you?
- 3Inspecting outdoor unit low voltage wires for damageDid this help you?
- 4Planning to call a professional service technicianDid this help you?
- 5checking furnace error blink codesDid this help you?
- 6changing air filtersDid this help you?
- 7inspecting limit switches and flame sensorsDid this help you?
- 8Checking power at the transformer and control boardDid this help you?
- 9Inspecting and testing the fuse with a batteryDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“My Nest thermostat was showing an E298 error, and after digging a bit it I found that the furnace/control panel doesnt have any lights or power.”source ↗
“The outside AC unit is also not running.”source ↗
“After that, I pressed the gray button next to it as it’s the safety reset apparently? It flipped the 3AMP switch up and I could hear a slight hum.”source ↗
“At this point I’m trying to determine whether the problem is simply the NOARK 3A device, or whether there could be another underlying issue such as the HVAC transformer, control board, power supply, or a short in the 24V circuit.”source ↗
“Thermostat is an ecobee, it seems to run the furnace for about 5-10 minutes then will restart. Screen goes black for about 2 minutes while the furnace keeps calling for heat.”source ↗
“My Ecobee reboots anytime my furnace faults , the four flashing lights will tell you what the fault is !”source ↗
“Ok I have a Goodman gcs90453bxa furnace Now my led light isn't on So I tested the power and have power at transformer Check for power on board using R and C no power at all So I'm thinking is the board is bad”source ↗
“I check the fuse using a battery and it must be blown dosent llok like thou”source ↗
Where this came up
People with this problem also raised
- 4Furnace won't turn on after new AC installation
- 3Why won't my new thermostat turn on the heat?
- 6New HVAC unit won't heat and makes clicking sounds
- 15Furnace lights up then immediately goes out
- 9Dryer sparked during reassembly and won't turn on
- 6Why is my furnace blowing cold air with a red blinking light?