I have a less than 2 year old, builder installed Navien water heater that has decided to be in a constant post-purge when it is not being used. The status alternates between POST-PURGE AND DHW-WAIT. I noticed this about a week ago as I heard a vibration upstairs and it was the water heater blower running and now water was flowing or had been flowing in the house. I cleaned the intake screen and cycled power. The blower stopped but then it started running constantly again. Any help would be great.