Today I restarted pumping down.
I turned on the scroll pump at 15:40 and waited until the pressure level became less than 10 Pa.
Then I turned on the turbo pump at 16:00 and the pressure is getting lower.
I will leave them running until tomorrow morning.
This mornig the pressure was 9.8*10-1 Pa, though it was 5.0*10-3 Pa yesterday...
I am suspecting the residual water caused the problem.
I took a data during thus vacuum test.
The measured output voltage from ANELVA M-601GC has a relationship between the pressure which is described as
P = 102*V-12,
where P is the pressure and V is the output voltage.
I roughly checked the pressure using this relation and it was like 10-6 Pa, though the displayed pressure was ~10-3 Pa.
The output voltage was not correct for some reason,
I will check the measured voltage and do the test again without venting.
I started pumping down this mornig and the pumps were working properly.
It seems that the vacuum gauge has a problem...
Although the pressure seemed decreasing, the pressure showen on the display was 9.8*10-1 Pa.
In addition to that, the output voltage from the ANELVA showed strange behavior.
Therefore I am suspecting the gauge has a problem.