Thermal latch vestibule · Velstraven

A small room of chapter 5. When you walk in, the room card reads: The service door's latch binds hot in its frame; the door stays shut.

Narrated walkthrough

Thermal latch vestibule from its entrance — Thermal latch vestibule: how to solve it

Getting there

Chapter 5, on the lowest floor. It opens off the choked cistern through the arch signed Thermal latch vestibule; a long passage also links it to the alignment records room.

What is wrong

Room card: "The service door's latch binds hot in its frame; the door stays shut." The brass latch is hot and swollen and binds at its middle against the cooler frame, and a failed heat branch keeps feeding it.

What you can work

Isolation: An insulated lever that parts the failed heat branch from the latch (handled; a second press reconnects it).
Latch: The hot brass sliding latch; it only slides once it is no more than 15 °C hotter than its frame.
Frame: The cool metal latch frame, with a service pad on its side.
Door: The service door; it opens by hand once the latch is withdrawn.
Reading lamp: Optional light to read by; it works none of the room's fittings.
Reading shutter: Optional second light angle from a high window; it works none of the room's fittings.

Solution

A nudge

The latch starts at 90 °C because the failed heat branch keeps feeding it. Parting the branch lets it settle toward room temperature instead of staying hot.

The full solution

Handle the Isolation lever (E / Square).
The latch starts at 90 °C because the failed heat branch keeps feeding it. Parting the branch lets it settle toward room temperature instead of staying hot.
What you see: "The insulating lever changes contact with the failed heat branch." The card counts 1 of 4: the failed heat branch is parted from the latch.
Cast Chill (Growth, Water, Water) at the Latch.
Metal shrinks as it cools. The cold wick pulls the latch down quickly; it frees once it is no more than 15 °C hotter than the 18 °C frame, about five seconds after the cast.
What you see: "A contacting cold wick draws heat from the latch." When it is cool enough the card adds: the latch and frame are back to a working fit.
Wait a few seconds, then Handle the Latch.
With the size difference gone, the latch has clearance to slide.
What you see: "The latch withdraws through its restored clearance."
Handle the Door.
Nothing holds the door shut once the latch is withdrawn.
What you see: "The service door opens." Then "Thermal latch vestibule settled."

Other ways that work

Heat (Fire, Fire, Growth) cast at the Frame warms the frame toward 90 °C instead, so it expands to meet the hot latch; after about six seconds the two fit and the latch slides, even if the branch was never isolated.
No spell at all: Handle the Isolation lever and wait about half a minute. With its heat source parted, the latch cools on its own until it fits the frame.
Chill alone also works without the lever, because the cold wick overrides the hot branch.

Watch for

Do not Heat the latch or Chill the frame: each makes the mismatch worse. The room says so ("a warmer latch only swells tighter in its frame"; "a colder frame only closes tighter round the latch").
The Isolation lever is a toggle. A second press touches the hot branch to the latch again.
Supply liquid on the latch only splashes off; it runs away before it can carry heat away.

If it goes wrong

Nothing in this room can fail. If the latch is still too hot, the Handle is refused with "The expanded latch still scrapes the frame." Wait a little longer, or recast Chill, and try again.

Achievements here

Latch Released: Solve the Thermal latch vestibule.

Spells used

Chill, Heat.