Honeywell WiFi Thermostat Low Temp Display Issue

The temperature DISPLAY on my RTH6580WF thermostat now only reads down to 40 degrees, despite being significantly below that in my workshop. I have digital and mercury thermometers located close to the RTH6580WF that is DISPLAYING 25 degrees. Over the last two winters, the RTH6580WF DISPLAY DID read correctly below 40 degrees. I can still set alarms on the Honeywell Total Connect app to email me when the temp drops below 32, but they no longer function since temperatures below 40 degrees are not recognized. I have been exchanging emails with Honeywell support over the last few weeks. They did admit that the issue was a result of their latest firmware update and it affects their entire line of WiFi thermostats. They also tell me that they have experts working on it, but I’m not optimistic at this point.

I’m fairly certain that there’s no way to modify the firmware through the API. I’m sure the only way to modify the firmware is to get an image dump of the ROM in the device, reverse engineer the binary by viewing it through a hex editor and find the point where they restrict the temperature reading.

Has anyone looked at this problem and found a workaround?

Thanks in advance!!

Hi @NasaBill:
Which device type are you using for the thermostat?
We don’t have an official device type integration yet. I am currently working on this and it might be released by the end of this quarter.
I can forward this issue to Honeywell’s Developer Evangelist to see if he can provide more information about it.


Hello Yaima,
I am currently using the Honeywell RTH6580WF WiFi thermostat. What I need to do is overwrite the minimum Temperature Display field in the firmware, since they are refusing to do it themselves. I spoke again with Honeywell yesterday and they said that have no plans to distribute the source code to me or anyone else. I asked for compensation for the thermostats that no longer perform as they did when they were purchased and they are looking into it. Needless to say, I will not be making any future purchases of Honeywell products as well as those products manufactured using Honeywell components and recommend that everyone else do the same.

Thanks for replying.

I did some research and found that the Radio Thermostat CT50 WiFi 7-Day Programmable Thermostat
by Radio Thermostat Company of America will DISPLAY down to 28F. They are around $125 from Since I have two of them I proposed to Honeywell that I would return their two RTH6580WF thermostats when I receive a check for $250.00 and a prepaid shipping label from them. A small price when you consider all the time and effort I have put in to this issue.

They replied:
Honeywell Corporate policy requires a valid proof of purchase when requesting a refund. Such documentation protects both the consumer and Honeywell.

In your particular situation, as a onetime exception to our policy, and with no further compensation or redress of any kind, Honeywell is amenable to providing a refund without a proof of purchase. The amount of the refund provided by Honeywell without actual proof of purchase, will be limited to the $250.00 you have asked for in the e-mail below.

Provision of your name and complete address, so a check can be mailed to you will be considered acceptance of this offer.

Honeywell Customer Care

My question to The Community is, should I accept their offer or do you feel that a resolution can be developed here between now and next fall that will satisfy my requirements?

This case is closed.

WARNING! The changes below are not to be made on a house installed thermostat as the low temperature set point will be below freezing, nor are they to be made on any other thermostat where freezing is a concern.

I bought this thermostat a few years ago for the house and later another for the garage. My plan for the garage was to keep it just below freezing so I wouldn’t have snow melting and water pooling all over the place. I was surprised when the temperature readout and set point bottomed out at 4.5C making it useless for that purpose. It also tops out at 37C on the upper end. I ended up just using it to heat the garage on demand when I used it for working in. That is until last week, when I decided to put my engineering degree to work.

Realizing that there was likely nothing I could do with the firmware to increase the range due to lack of source code and limited time, my plan was to try and shift the range down to where I wanted to use it. Armed with a thermocouple, and an environmental chamber I began the task of trying to accomplish that. Upon removing the cover, I discovered that there were three thermistors (RT101, RT102, RT103), each with a secondary resistor in line with it (R100, R101, R102). I wasn’t going to touch the thermistors, only these secondary resistors for range adjustment. I experimented with different values of R100, R101, R102 and found that changing them from 10k 1% to 15.4k 1% shifted the range by 10 degrees C in the direction I wanted…

My thermostat now will work over the range of -5.5C to 27C but will still display from 4.5C to 37C
Now if I want to set the temperature in my garage to a specific value, I would set the thermostat set point to 10C higher than the desired temperature.

Desired Temperature (deg C) . Thermostat Setpoint/Reading (deg C)
-5.5 . . . . . . . . . . . . . . . . . . . . . 4.5 (Min Set Point / Readout)
-5 . . . . . . . . . . . . . . . . . . . . . . .5
0 . . . . . . . . . . . . . . . . . . . . . . . 10
5 . . . . . . . . . . . . . . . . . . . . . . . 15
10 . . . . . . . . . . . . . . . . . . . . . . 20
15 . . . . . . . . . . . . . . . . . . . . . . 25
20 . . . . . . . . . . . . . . . . . . . . . . 30
25 . . . . . . . . . . . . . . . . . . . . . . 35
27 . . . . . . . . . . . . . . . . . . . . . . 37 (Max Setpoint / Readout)

This change was tested without it connected to a furnace so hopefully there is something I have not overlooked. With winter coming, I should have plenty of time to validate my changes and possibly shift the range lower in temperature, maybe by another 5C for a range of -10.5C to 22C.