The short answer
To reset a Lennox thermostat in Northern Virginia, restart it rather than factory resetting it. A restart reboots the thermostat and keeps your schedule and the installer’s setup. On an S40, press and hold the small reboot button with a paper clip for about six seconds; Lennox says no settings are lost. On an S30 or E30, the restart is in the menu. A factory reset wipes the installer settings, and Lennox itself says that one should be done by an HVAC contractor.
Restart or factory reset: which one you want
The two words get used for the same thing, and they aren’t. A restart is a reboot. The thermostat shuts down, comes back up, and remembers everything: your schedule, your Wi-Fi, and the installer setup that tells it what equipment it’s running. A factory reset erases all of it. The thermostat comes back as if it just left the box and walks through installer setup again.
Lennox’s support page is plain about who should do the second one: a factory reset “should be performed by an HVAC contractor,” because the setup after it is complex. On a heat pump, those installer settings include how the thermostat runs the outdoor unit and when the backup heat comes on. Get them wrong and the system still runs, just on the expensive heat.
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Model by model
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| Thermostat | Restart (keeps settings) | Factory reset (erases them) |
|---|---|---|
| S40 | Paper clip in the reboot pinhole on the thermostat, hold about six seconds. Or Settings, Advanced Settings, View Support Service Control Center, Equipment Settings, Reset, Restart Thermostat. | Reset thermostat, inside the Support Service Control Center. It restarts installer setup. |
| S30 and E30 | Menu, Settings, Advanced Settings, Restart. On an S30 you can restart the Smart Hub, the thermostat or both. | Reset thermostat, inside View Dealer Control Center, which Lennox marks for installers and technicians only. |
| M30 | RESTART, on the installer menu. | RESET SETTING, on the same menu. It puts every parameter back to factory settings. |
| Older iComfort Wi-Fi | Hold the Lennox logo on the front screen to open dealer settings, then pick Restart. | Leave it to the installer. |
| ComfortSense 7500 | No restart button in Lennox’s guides. Turning the furnace switch off and back on reboots it, since the furnace powers it. | RESET SETTINGS on the installer menu. Lennox calls it a last resort: it erases all programming. |
Before you restart anything
Is the screen just asleep? Lennox thermostats have a Power Save setting where the screen stays blank until you touch it. Touch it before you assume it’s dead.
Does it say System Under Test? Lennox says that one usually shows up after a power interruption, while the thermostat looks for the indoor and outdoor controls. The outdoor control sometimes takes longer to boot and misses the roll call. Lennox’s fix: recycle power to the system. Turn off the furnace or air handler switch and the breaker for the outdoor unit, then turn both back on.
Is there an alert on the screen? Photo it before you restart. A restart can clear what’s showing, and the alert number tells a tech what the equipment reported. Lennox Service Urgent alerts covers the common ones.
Is it only the app? If the thermostat heats and cools fine but the app says offline, restarting the thermostat rarely fixes the router. Lennox thermostat not working has Lennox’s Wi-Fi checklist.
What a restart won’t fix
If the thermostat restarts fine and the house still won’t heat or cool, the thermostat was the messenger. The alert it shows is the furnace, air handler or outdoor unit talking.
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| What you see after a restart | What it usually is | Our price |
|---|---|---|
| Screen stays blank, touch or no touch | No 24-volt power reaching it: a tripped control breaker, a blown fuse or a broken wire | Priced in writing |
| Powered, wired right, still dead or frozen | The thermostat itself failed | $300 to $640 |
| System Under Test that won’t clear | The outdoor control isn’t answering | $550 to $1,180 |
| An alert code on the screen | Equipment trouble (Lennox error codes) | Depends on the code |
The diagnostic is a flat $99, and the repair price comes in writing before we touch anything. A thermostat replacement includes wiring it, mounting it and setting it up for the furnace or heat pump it runs, backup heat included.
Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. On a furnace, for $229 (regularly $467) we also pull the blower wheel and clean it blade by blade.
Every Lennox code in one place: Lennox error codes. Other brands too: furnace and AC error codes.
Call or book a Lennox repair
Call (703) 997-9757. We answer day or night. Or book online and pick a time. The diagnostic is a flat $99, and you see the repair price in writing before we touch anything. Furnace running fine and you want to keep it that way? Book the $67 heating check from goswiftpro.com/cookiesoffer (book by November 30) and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276. More on Lennox repair in Northern Virginia.
Questions people ask
How do I reset my Lennox thermostat without losing settings?
Restart it. On an S40, hold the reboot pinhole button for about six seconds with a paper clip; Lennox says no settings are lost. On an S30 or E30, use Menu, Settings, Advanced Settings, Restart.
Should I factory reset my Lennox iComfort thermostat?
Usually not. Lennox says a factory reset should be done by an HVAC contractor, because the setup afterward is complex. Try a restart first.
What does System Under Test mean on a Lennox thermostat?
It usually shows after a power interruption, while the thermostat looks for the indoor and outdoor controls. Lennox says recycling power to the system may clear it.
It’s a small pinhole button on the thermostat. Press and hold it with a paper clip for about six seconds to reboot. Your settings stay.
