The short answer
ComfortLink II is Trane’s communicating control system, and in Northern Virginia homes it’s usually an XL850 or XL1050 on the wall. Instead of only switching the furnace or heat pump on and off, a ComfortLink II thermostat talks to communicating Trane equipment over a 3-wire connection, reads how it’s running, and shows an alert when something fails. The XL1050 adds zoning. The XL824 looks a lot like them but is a regular 24-volt thermostat, and the UX360 is the control for Trane’s newer Link system.
Which Trane thermostat is which
From Trane’s installer guides for the XL824, XL850, XL1050 and UX360:
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Swipe to see all columns →
| Model | What it is | What it runs |
|---|---|---|
| XL824 | Smart thermostat, standard 24-volt wiring, not ComfortLink | Up to 5 stages of heat and 2 of cooling |
| XL850 (TCONT850) | ComfortLink II communicating control | Communicating Trane indoor units, with a communicating or a non-communicating outdoor unit |
| XL1050 (TZON1050) | ComfortLink II communicating control with zoning | The same, plus zones: one zone panel runs up to 4, a zone expander adds more |
| UX360 | The control for Trane’s Link system | Link equipment, over Link’s own 4-wire connection |
ComfortLink II and Link are different systems with different wiring, so which control fits depends on the equipment you have. That’s a question for the tech looking at your system, not the box.
The $67 Heating Check
We check your furnace, heat pump or boiler before winter. Through December 31. See the offer
What the alerts mean
Because it talks to the equipment, a ComfortLink II thermostat can tell you what failed. Critical and Major alerts show as a yellow icon at the top right of the screen; Minor ones sit on the Diagnostic screen, and the history keeps 30 days. The one we see most is Err 126, lost communication (Err 126 guide). Others, like 79 and 157.00, are in our Trane error codes guide, and American Standard’s twins of these controls use the same numbers (American Standard error codes).
Common problems and what to do
- Blank screen. Almost always power to the indoor unit: a switch, the furnace door, a clogged drain or a tripped breaker (blank screen guide).
- Frozen or stuck. Reboot it: Menu, Settings, Reboot (how to reset a Trane thermostat).
- Offline in the app. Wi-Fi off and on under Menu, Settings, Network, Wireless, then reboot. The house keeps heating while it’s offline.
- An alert that comes back. The thermostat is reporting a real fault in the equipment. Write the number down and call.
Don’t factory reset a ComfortLink II thermostat to fix a glitch. Restore Factory Defaults erases the installer’s setup, and a communicating system may not run right until a tech sets it up again.
Replacing one
A communicating Trane system wants a communicating Trane control. Put a Nest or another regular smart thermostat on it and it runs as a basic system, without Trane’s alerts (a Nest on a Trane). Replacing a thermostat runs $300 to $640, with the exact price in writing before the work. A diagnostic visit is $99, and you get the problem and the price in writing before any work starts.
Our heating check is $67 per system, through December 31: furnace, heat pump or boiler. If the alert points at the heat pump, our heat pump repair page covers what we fix, and every brand’s codes are in our error codes and warning lights guide.
Book it
Book the heating check, call (703) 997-9757, or book online from goswiftpro.com/cookiesoffer 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.
Questions people ask
What is Trane ComfortLink II?
Trane’s communicating control system. A ComfortLink II thermostat, like the XL850 or XL1050, talks to communicating Trane equipment over a 3-wire connection, reads how it’s running and shows alerts.
Is the XL824 a ComfortLink II thermostat?
No. The XL824 is a smart thermostat on standard 24-volt wiring. The XL850 and XL1050 are the ComfortLink II models.
What’s the difference between the XL850 and the XL1050?
Both are ComfortLink II. The XL1050 adds zoning: one zone panel runs up to 4 zones, and a zone expander adds more.
Can I replace a ComfortLink II thermostat with a Nest?
It will run a communicating Trane as a basic system, without Trane’s alerts. A Trane communicating control keeps everything working.
How do I reset a ComfortLink II thermostat?
With the system idle, press Menu, then Settings, then Reboot. Or turn off the furnace or air handler breaker for 20 to 30 seconds. Skip the factory reset.
The system we put in first
Built to take a beating. Put in by our crew.
Heat lamps, snow and rain on one outdoor unit: that’s Trane’s own film. We’re a Trane Comfort Specialist, on Trane’s own dealer locator, and when you pick a Trane, our crew puts it in.
Films: Trane’s own.
