Our 4 month old Serenity stove quit working right before Christmas. It will run for 15-20 minutes then shut down. The hopper has pellets and the fire pot is clean. I’ve changed the 52C wires to the spare provided, still won’t run. The controller NTC1 is not shaded, NTC2 says ERR and the limit spot is shaded. Any ideas? 4 months old and only 15-20 bags ran through it. The company is impossible to get hold of by phone and no email replies.