Safiry star sensor

I have upgraded to a cerbo GX and transferred all sensors across. I have fitted a piezo resitive 50mbar tank sender to the diesel tank which works great. I then decided to install a Safiery Star tank senser to the water tank. I have xset it up with single green LED for small tank but the sensor shows 238cm and no matter what I do it will not clear and read correct value. The temperature and battery voltage appear correctly. I have followed everthing AI has thrown at me but it still reads 238cm . Any ideas would be appreciated. Getting support from Safiery is one of the worst tech support Companies I have ever dealt with so if you are thinking about buying one BEWARE the email they give for support comes back as Mail cdelivery system