What does the pressure switch on an induced-draft furnace prove before ignition is allowed?
- That the gas supply pressure at the valve inlet is high enough
- That the circulating blower is moving air across the heat exchanger
- That the air filter is clean enough for the furnace to run safely
- That the inducer is moving air through the heat exchanger and vent
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D. That the inducer is moving air through the heat exchanger and vent
The switch senses the negative pressure created by the draft inducer, confirming that combustion air is flowing and the vent is not blocked. It does not measure gas pressure, despite its name.
Reference: Appliance manufacturer installation and service instructions
A furnace's flame rollout switch has tripped. What does that indicate?
- The thermostat has been set above its upper limit
- The gas supply pressure dropped during the cycle
- Flames or hot gases escaped the burner compartment
- The condensate drain has filled up with water
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C. Flames or hot gases escaped the burner compartment
Rollout switches sit near the burners and trip when flame leaves the combustion chamber, usually because the heat exchanger or vent is blocked or the unit is overfired. The cause must be found before resetting.
Reference: Appliance manufacturer installation and service instructions
The temperature and pressure relief valve on a storage water heater opens on excess pressure or when the water reaches about what temperature?
- 120 F
- 160 F
- 210 F
- 250 F
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C. 210 F
Standard T&P valves open at about 210 F, just below boiling at atmospheric pressure, so that superheated water never builds up in the tank. 120 F is a common thermostat setting, not a relief setting.
Reference: ANSI Z21.22 relief valves; water heater manufacturer instructions