K2639 relais don't stop more when it start work

Hi, I bought the Kit K2639, I have tested it like write in the manual and all was in ordering.
Now that I have installed kit, it don’t works correctly because when pump start (led 1 and led 4 red became on, it always work and don’t stop with work, when there is no more water.
I must off power supply any time so (sometimes) green led ld3 become on and pump off. But every time it start, it don’t stop.
Pump is 220V 400W less of 3A that relais support.
Can you help me?
Thank you very much

The sensor cable is either too long and/or too capacitive. Check if unit works fine with a shorter cable.

Many thanks, I need 2,5 meter cable, and I have used the same for house allarm that is shielded with mass.
Can you please give me a right cable and diameter to use for this distance?
It runs with 220V is this the problem? I have measured resistance Rx10 and Rx1K but is = zero (my tester have no more scale)
Is there a way to misure if cable is right and what must be resistance?
You understand I am a beginner that like do it yourself, may I have your help.
(I am italian, excuse me for my English school).

The resistance is not the problem, capacitance is the problem.
Furthermore, running the sensor wires together with the 230VAC wires will cause troubles.

Hi, I have changed cable. Now I have 2.5 meter Prospecta H0052 LI-YCY 2X2X0,25 cable. I have also wired the sensor out of 220VAC. Where may I connect massa (ground) to the kit or to what?
Thank you for reply. Massimo.

Kit has no earth connection.