The LCD screen of my Honeywell CMS927 thermostat mostly stopped working.
See here how I fixed the display using a toaster.
(Also applies to the CM927 - the S indicates it was sold with the receiver. The 921 is the 1 day rather than 7 day version.)
The site for user manuals:
https://heatingcontrols.honeywellhome.com/
I have another video with the background music removed here: https://www.youtube.com/watch?v=fWfP9c_NNiM
Inspiration from:
https://www.youtube.com/watch?v=6cnCDOfCafs