I have Lennox heat pump about 10 year old. The control center is called Harmony II. There is a red light which has been on/off for a few years now. The mannuel says it indicates need of service. The service contractor tried very hard and could not fix it or find out why (I do not have confidence in them any way). The cooling and heating seem to be working OK. Any suggestions?

Leave it alone. When and if it breaks down you will find the problem.