ResMed VPAP III, VPAP III ST, VPAP III ST-A Service Manual page 51

The latch
1 Turn the water chamber base upside down.
2 Gently pull up and away from the chamber until separated from the base.
3 Take the new latch and insert the feet with locking tabs into the slots as shown below:
4 Push the tab at the top of the latch into the slot at the top of the heater plate.
50 VPAP® III, VPAP III ST, VPAP III ST-A Service Manual
Ensure the tab latch clicks
securely into both slots