I know but 300 Pascal should be reached at 300C not at 20C!
How do you know this? Perhaps I misunderstood the brief instructions in Jed's document:
Heat production
1. Valve off the vacuum pumps and set deuterium pressure to 0.75 - 2.25 Torr (100-300 Pa).
Do not exceed 45 Torr (6000 Pa). Record pressure history.
2. Raise the temperature 100°C with the sheath heater. This should generate some excess
heat.
3. If there is no excess heat, raise the temperature higher