Ducted secondary air fuel-fired water heater LDO detection

摘要

A fuel-fired heating apparatus is disclosed. The apparatus comprises a combustion chamber 20 and a fuel burner 24 disposed within the combustion chamber. The fuel burner is progressively cloggable by particulate matter contained within the primary combustion air delivered to the burner during the firing of the burner. A first air supply structure supplies primary combustion air 32 to the fuel burner 24 . This structure prevents the combustion air from being exposed to the interior of the combustion chamber on its way to the fuel burner. A second air supply structure 42 receives secondary combustion air from outside the combustion chamber and discharges the secondary combustion air into the interior of the combustion chamber at a discharge velocity for flow through to the fuel burner. The second air supply structure is progressively cloggable, at a greater rate than the fuel burner, by particulate matter entrained in the secondary air, in a manner which progressively reduces the discharge velocity. The apparatus also comprises a system for monitoring the discharge velocity and responsively terminating the operation of the fuel burner when the discharge velocity decreases to a predetermined level.