Heating Flashcards
What is the recommended gap for ignition spark?
1/8”
Which pilot system needs to be dealt with carefully because it may damage some electrical meters when taking the flame current?
The single rod system
What builds up on HSI and flame rods and impedes the current flow for flame proving. Can it be fixed?
Develops and oxide coating. Flame sensor can be cleaned but replacement recommended for HSI
What are HSI made out of and which is more brittle
silicon carbide and silicon nitride. Carbide is more brittle
How many volts is connected to the hot surface igniter?
115 VAC
Can an HSI be used as a flame sensor?
Yes
What should you use to clean a flame sensor?
Scotch Brite pads or 000 Steel wool
What are the two ways you can prove flame? Which is the most reliable and why
Flame conductivity and flame rectification. Flame conductivity is not used because it can’t distinguish between flame and short circuit (two rods)
What is the difference between a single rod and two rod ignition system
Single rod has one rod to do both ignition and flame sense. Two rod has one for each function.
What is flame ionization?
Heat from the flame causes the molecules between the electrodes to collide forcefully and it knocks some electrons out of the atoms, producing ions. Positive ions are attracted to the negative electrode while negative ones are attracted to the positive electrode.
Explain Flame Rectification for a short answer question on the test
A flame and flame rod/ground become a device that converts alternating current into direct current. The flame sensor is energized with 100 VAC, flame ionization occurs in the flame and a 4-6 micro amp DC signal returns to the module to verify flame via ground. For best operation the area of the ground electrode must be at least 4 times that of the flame rod. (10x is optimal)
In Flame rectification which of the electrodes is larger?
The ground electrode (burner ground) is much larger than the flame rod. Minimum of 4:1 ground to flame rod. Optimal is 10:1
In flame conductivity systems which electrode is larger?
There are two electrodes, flame rod and ground and they have similar or equal surface area.
When the flame rod is positive: Current flows
When the flame rod is negative: Current flows
What kind of signal results from this?
More current flows
Less current flows
Effectively results in a pulsating DC current that is required to pull in the flame relay
True or False:
The larger the ratio of ground area to flame rod area, the greater the flow of current in the proper direction
True: larger ratio results in greater flow of a rectified current
In a flame rectification system, what happens if a short circuit occurs?
The module received an AC signal and the system will shut down.
How do you solve the problem with flame proving if the micro amp signal being received is not strong enough to prove flame?
You can adjust the areas of the electrodes immersed in the flame until the signal is strong enough to prove the flame
What is a Safe-Start check?
Ignition module checks to ensure there is no false flame signal, if a flame is detected it shuts everything down and goes into lockout
What is a post purge cycle?
On some furnaces the inducer fan continues to run after the burners are shut down.
What else starts when the ignition cycle starts?
A lockout timer. If the pilot isn’t proven in the allotted time the module shuts off gas and spark.
What is a recycling control? What kind of appliances are not allowed to have these l?
If a furnace tries to restart even once it’s considered a recycling control.
Continuous trial is not allowed for propane appliances or direct ignition systems.
How long is the blower off delay setting in a furnace?
90-180 seconds most common
Furnace blower off delay is adjustable from 90-240 second delays
What two factors do you check when calibrating thermostats?
Operating temperature and operating differential
What is the operating differential of a thermostat?
It is the range of temperature required to make the thermostat open or close
What is a common cause of a gas valve failing to close?
A short circuit
What is the minimum gas pressure needed for a gas valve to operate properly
2” wc to overcome the weight of the diaphragm and spring tension
How do you determine a faulty electromagnet?
A continuity test
High ambient temps weaken electromagnets over time as well
What is the difference between a redundant gas valve and a combination gas valve?
Combination incorporates three major components: solenoid valve, diaphragm valve and a pressure regulator.
Redundant valve incorporates two components: diaphragm valve and solenoid valve
What is the main difference between an intermittent pilot gas valve and a direct ignition gas valve?
The direct ignition gas valve has no pilot connection
When using electronic ignition, what is the process of proving the flame called?
Flame rectification
What is the minimum flame rod to ground electrode area that is immersed in the flame?
1:4
What is the cause of yellow tipped flames?
Not enough airflow
Yellow flames indicate incomplete combustion
What causes flame lift?
Velocity too high
What causes a waving blue flame?
Drafts/ air blowing on burner, cracked heat exchanger
What causes flashback?
Not enough gas pressure
What is the cause of the main burner flame being too large?
Too much gas
What is the cause of noisy flame?
Too high velocity
CO ppm of 50 has what effect?
.0005 % CO is the concentration allowable for 8 hour exposure
CO ppm of 4000+ has what effect?
0.40 % and above are concentrations which are fatal with exposure less than 1 hour
Yellow flames indicate what?
Incomplete combustion, which causes Aldehydes and CO
After a safe start check, the ignition sequence initiates and has an ignition timer, how long is it?
17-34 seconds
How hot does a hot surface ignitor get? How many volts goes to this?
2600°F
115 VAC
What is the difference between a pictorial and a schematic diagram?
Pictorial = connection and has wiring connections and wire colours * drawn as if the appliance is in standby (no call for heat)
Schematic = ladder and is helpful in determining the sequence of operations for troubleshooting *drawn with the appliance in standby (no call for heat)
What is the recommended first step when assessing a wiring diagram?
Locate the transformer
