Combination pressure and temperature limit control for a fuel-fired, forced draft heating appliance combustion product exhaust system

A forced draft, fuel-fired heating appliance comprising:

• heating means operative to generate combustion gas during use of said appliance;
• exhaust means for exhausting the combustion gas from said appliance to a location remote from said appliance, said exhaust means including a draft inducer fan having a housing with an inlet for receiving the combustion gas, and an outlet for discharging the combustion gas,
• said housing, during fan operation, having a negative pressure interior region;
• and
• control means for shutting said appliance down in response to a predetermined pressure increase within said negative pressure interior region of said fan housing, or to the presence of an undesirably high temperature within said fan housing, said control means including:
• pressure sensing means for permitting a flow of ambient air to be drawn therethrough into said negative pressure interior region of said housing during fan operation, sensing the magnitude of said flow of ambient air, and precluding operation of said appliance when said magnitude falls below a predetermined level, and
• temperature sensing means for sensing the temperature within said housing and essentially precluding the flow of ambient air through said pressure sensing means in response to a sensed temperature exceeding a predetermined temperature.

A forced draft, fuel-fired heating appliance comprising:

• heating means operative to generate hot combustion gas during use of said appliance;
• vent hood means for receiving said hot combustion gas and having an inlet for receiving ambient dilution air for mixture with and cooling of the received hot combustion gas;
• draft inducer fan means associated with said vent hood means and operative to withdraw and then discharge into a vent pipe connected to the fan means outlet combustion gas and ambient dilution air from said vent hood means, said draft hood means, during operation thereof, having a negative pressure interior region;
• and
• control means for sensing an obstruction in either the vent pipe or said vent hood means inlet during operation of the appliance and responsively shutting down the appliance, said control means including:
• pressure sensing means for permitting a flow of ambient air to be drawn therethrough into said negative pressure interior region of said draft inducer fan means during operation thereof, sensing the magnitude of said flow of ambient air, and precluding operation of the appliance when said magnitude falls below a predetermined level, and
• temperature sensing means for sensing the temperature within said draft inducer fan means and essentially precluding the flow of ambient air through said pressure sensing means in response to a sensed temperature exceeding a predetermined temperature.