Complete 1 system a/c repair and preventative maintenance check. Reseated Thermostat on wall and system is working fine after. Could not determine whether it was from the last visit out so there is no charge for today. Explained to the customer that if it happens again the thermostat will need to be replaced. CTK04 Thermostat on the wall. Customer does have a 10 yr P&L warranty. Let him know that normally the extended warranties will cover thermostats but will need to figure out if happens again. Recommended membership and the customer said it' not cost effective for him because of the extended warranty. They are getting the systems serviced every year.