Only the first touch , after that nothing
I have touch the sensor out put wire for it to reset, or hold it and then it works perfect.
Just tested, it takes about 90s for it to trigger the relay again if nothing is detected.

 

The testing procedure should be as follows:
To start both sensors should be touched simultaneously to represents a full tank and the relay OFF. Remove finger from HIGH sensor, relay still OFF. Remove finger from LOW sensor, relay ON.
Touch LOW sensor again and relay still ON. Hold finger on LOW sensor and touch HIGH sensor, relay OFF

 

Exactly but that only works if I'm touching either of the sensors output wires.
Otherwise it will react to the first touch and then nothing till about 90 s later where the relay triggers again.

 

Even the 90s is not exact, now it took only 30s

 

I'm getting confused what exactly happens step by step following my testing procedure?

 

Hehe, who wouldn't....
It works exactly as you wrote it down, BUT, only if I'm pinching one of the sensor output wires at the same time.

If I don't only first touch gets registered and every other touch is very delayed.
This delay is changing from couple seconds to over a minute.
I can immediately "fix it" touching one of the sensor output wires.

 

Where exactly are you pinching the output wires?

 

Just tested with tweezers in my hand, and anywhere from pin 4 towards sensors will work.

Starting to think that I have the MAGIC TOUCH!

EDIT
Anode of the diode as well but no further that way.

 

This is getting crazy.
Do you have a scope or meter for some testing?

 

No scope, only multimeter

 

A meter will help. Fasten the +meter lead to any junction connected to pin4 of the 555 and minus lead to ground for hands free operation.
Read voltage for each step of my procedure without pinching any sensor wires.

 

Plugged in 4.4V
To start both sensors should be touched simultaneously to represents a full tank and the relay OFF. 0V
Remove finger from HIGH sensor, relay still OFF. 0.02V
Remove finger from LOW sensor, relay ON. 0.46V (not ON)
Touch LOW sensor again and relay still ON. 0V (still not ON)
Hold finger on LOW sensor 0V
and touch HIGH sensor, relay OFF 0V (still OFF)

After that I removed my fingers from both sensors and about 30s later the relay turned ON.

 

Voltages from the working board (same power supply)
Plugged in 3.5V
To start both sensors should be touched simultaneously to represents a full tank and the relay OFF. 0V
Remove finger from HIGH sensor, relay still OFF. 0.12V
Remove finger from LOW sensor, relay ON. 3.52V
Touch LOW sensor again and relay still ON. 1.54V
Hold finger on LOW sensor 1.54V
and touch HIGH sensor, relay OFF 0V

 

OK that's weird.
Now repeat readings pinching wire as needed to operate correctly.

 

From the first test it appears the anode of D1 is not connected to pin3 of the 555.

 

With the meter attached my touch is no longer MAGIC
3.7V all the time

 

Measured pin 3 to Diode anode measured 2.2K so looks like it is connected

 

100%
Verified as well

 

Check cathode to pin4 should read zero ohms.

 

Yes, zero ohms pin 4 to cathode