ring the manufacturer or email they might say send it back and send you another one it sounds like it shorting out somewhere (which is not good my central heating thermostat does that lol) or just buy a new one like forby3 says or do both lol
as long as it is not out of water it should be fine it maybe condensation in the thermostat at the top try drying it out on a radiater for a day and then try it again see what happens
It does sound like the bimetal strip is sticking slightly and releasing last minute so I really think you need to contact the manufacturer or go back to the shop. They should be ok as long as you are polite