De Dietrich 81990206 sight glass

A De Dietrich sight glass is a housing part that provides a visual window into the combustion chamber. During burner operation, it allows the service engineer to observe the flame shape, colour and stability without opening the boiler door. On burners of this class, the sight glass is typically mounted on the front panel or the burner door, secured with a retaining ring and sealed with a high-temperature gasket. Parts of this type are selected exclusively by the boiler model and the exact mounting position on the housing. There is no universal sizing or rating; the glass diameter, thickness, and the fixing hole pattern must match the original panel. When replacing, inspect the gasket for hardness or cracking — a compromised seal can allow false air into the chamber or cause flue gas leakage. The glass itself can become clouded by soot or cracked by thermal shock; any obscurity or damage means the part must be renewed to maintain a clear view during commissioning and servicing. The De Dietrich 81990202 sight glass is listed with catalogue article 336.748.002 and is found in the boiler housing parts category. As with all housing items, confirm the correct model and position before ordering.