There are a tremendous number of doors, blocks, and other obstacles impeding Samus Aran's progress on Planet ZDR--however, most of them require an upgrade of some kind to be opened, unlocked, or destroyed. There are exceptions, such as the Thermal Doors, which need to be opened in a different way than most others in Metroid Dread.
Mechanisms that are locked due to environmental reasons can be a bit annoying to figure out if one only tries to brute-force them open with one's various bounty hunter tools, so, at times like these, it's important to remember that Metroid Dread is a game all about exploration and retracing one's steps. Doing so will cut down on the frustration of getting stuck as well as make it more possible for players to figure out how to proceed.
What Are Thermal Doors?
Thermal Doors appear on the map as doors covered in a red design. There are regular Thermal Doors, which appear vertically, as well as Thermal Trap Doors, which are horizontal in nature. On one's map, closed Thermal Doors will be opaque while open ones will be translucent yet still display the red design that makes them easy to identify as Thermal Doors.
Due to Planet ZDR being powered by thermal energy, players will need to use this mechanic a few times over their playthrough, as certain areas simply won't have power unless Samus redirects energy to the desired spots, which, in turn, will open up certain Thermal Doors. The first time players will encounter this mechanic will be in the planet's hottest region, Cataris, though this won't be the only time thermal energy is needed.
How To Unlock Thermal Doors By Redirecting Thermal Energy
In every area where Thermal Doors appear, there will be an interactive device somewhat nearby that will allow players to redirect thermal fuel, which will unlock closed Thermal Doors in the area, however, will also lock some that were previously opened by default. Players should not worry about the latter, as this is actually the game's way to prevent players from backtracking too far as well as potentially getting lost and confused.
Connected to these interaction devices are large red pipes that have many glowing orange rectangles on their sides. Players can potentially follow these red and orange pipes to help them find the thermal fuel interactive devices if they cannot find them by normal exploration.
Metroid Dread is available on the Nintendo Switch.