I know that our walk in tub has a purge cycle that comes on about 20 minutes after the tub is empty but it also comes on while bathing and while the tub is full of water and cannot be turned off for at least 30 seconds. Our tub has been replaced after 3 years of discussion by the American Standard but uunfortunately, it still happens sporadically and I don't understand why AS cannot fix it. They won't respond to us.