Similar to candles, your unit flames are not exactly “clean”. The result is a carbon buildup on glass and logs. Some build up is to be expected and can easily be removed when cleaning. However, an excessive amount of buildup can indicate a problem and should be inspected by a qualified gas technician.
Afterhours Emergency Service
Brantford & Area: 519-756-4374
Cambridge & Area: 519-621-8827