Water temperature alarm Perkins 4.108

[pr2501]

I have new cooling water in the system and I get the alarm from the water sensor next to injector 4. (if i take the wire down alarm stops)
But I can put my finger next to sensor and I will not get burnt.
Still the other sensor which displays temperature works normally. As the engine warms up the temperature displayed also grows. And somewhere between 60 and 70 degrees Celsius I get the alarm.
And then I can not get ride of it until the engine cools down totally.

Here I would like to know if I have to bleed the water system?

Or it is that my engine sensor is triggering the alarm to soon?