Had a no heat call today on a system I was at a month ago for regular maintenance and found today that the flame sensor was dirty I was reading .2 ua so I cleaned the flame sensor check my ua and it was back up to 2.8 after cleaning my problem with that though was that I cleaned the flame sensor on the maintenance call and was reading 2.8 ua after cleaning it then as well I got to looking at the work history on this call and saw that our company (i have only worked with this company for the past 7 months) has been out there 3-4 times a year cleaning this flame sensor and has even been replaced twice any suggestions as to why this may be getting dirty so quick so I can get this problem resolved and keep a good loyal customer from getting angry with the company