You could have one of two problems
Youhave a faulty solonide valve , (only hope you have a flow rate gauge.
Your reciever / control unit need to be sent back.
Mine had to be redon after 5 years.
Almost for got one do you use soap solution to check if any of the fittings are leaking via bubbling (a teaspone of dishwashing soap in a pint of pure water , di ionized , etc)
I check my valves and tank fitting every time I install a new tank.