Just like "close door" elevator buttons and press-to-walk street signs, hotel thermostats are a notorious public placebo. You see the rig on the wall and get to feel like you have some modicum of control, but in reality, that thermostat will only let you go to 22C, maybe 21C if you're lucky. But after that it's useless -- unless you know just the right buttons to push.
Assuming your hotel comes stocked with Honeywell's Inncom line of hotel thermostats, there's a secret VIP mode that overrides any preset temperatures and deactivates motion sensors. Simply use the following instructions as discovered by YouTube user rcslex, and the bedroom freezer/sauna of your dreams is all yours:
- Press and hold the "display" key
- Tap the "on/off" button (while still holding "display")
- Tap the "up" arrow button (again, while still holding "display")
- Release the "display" button