My boiler keeps giving me a F1 code. We have replaced the overheat stat and the thermister this worked for a while. However, the problem is happening again. when we change the temperature on the boiler ie from 45 degrees F to 55F or 55 to 65, works for a while without us having to reset it and then after a few days the same problem occurs. Could it be the memory board as suggested by the engineer that was called out.