Bissell 1623e tank emptying?

After a short time of normal operation the solution tank will just empty via the normal front jets even when using the hand tools. It appears that the trigger switch is operating some sort of valve/solonoid as clicking can be heard under the main housing but no matter how many times you pull and release the trigger the tank will empty from full in around a minuite. you cant stop it. Leaving it for a while and all can be well again from anything from 5 to 30 mins then It'l just empty again