Fireplace was not working. Customer explained that fireplace would not light. Tried to light pilot several times with no luck. Cleaned flame sensor and tried to light again. After allowing pilot light to set for over 1 1/2 mins, pilot stayed lit. Cycled system and ran for over 15 mins with no issues. Diagnosis is that the flame sensor is getting weak. There is a possibility that the gas valve springs are also getting weak. Instructed the customer of her options. The customer is going to try to keep the flame sensor clean. If issues arise again, due to age and style of fireplace, Darboy stone and brick was recommended for replacement of parts or unit. Customer will call if they need any more help from us. A cleaning was not needed for this unit, diagnosis fee was charged instead. System operating normal at this time. Job complete.