kamakaze

Anyone have any ideas?

I am a new owner of a Gulf Coast LX5000 that came with a house I just bought. We started it up and immediately received a rhnf error which the technician explained was a "flow error." However, since the water was flowing he stated the in.therm heater was bad and replaced it. The new heater worked fine for about a week and then would throw an occasional rhnf error and the temperature read-out would sometimes read up to 5-7 degrees below the actual temperature of the water (verified with a separate thermometer). Thinking the new heater was defective we had the technician back out and he replaced the in.therm heater again under warranty. Since then, the second replacement heater continues to very occasionally throw an rhnf error and seems to rarely ever reach the set temperature (we have it set to 101 but it seems to read between 94 and 100 and run continuously). It seems to heat well as I have a thermometer that will show the water as 103 while the hot tub will say 94. My question is, is this temperature read-out fluctuation normal or are these Gecko in.therm heaters that hit or miss? It seems to run almost constantly (granted it's usually less than 10 degrees outside). Any advice or should I just have the technician replace the heater again? Thanks!