1. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 1 7.3.2 Identifying the Components and Operating Characteristics of Electronic Ignition Systems Electronic ignition systems apply the flame rectification principle outlined in module 7.3.1. Service technicians must understand the operation of electronic ignition systems to successfully service mid and high-efficiency furnaces and boilers. In this module, you will learn to: 1.The purpose and function of electronic ignition systems 2.Types of electronic ignition systems 3.How to purge air and gas/air mixtures before placing electronic system-equipped appliances into service

2. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 1 Identifying the purpose and function of electronic ignition systems The purpose of electronic ignition systems is to provide a verifiable ignition source to establish the main burner flame and to monitor the flame throughout the burner operating cycle. Development of electronic ignition systems has been an important step in improving gas appliance efficiency by eliminating the need for standing pilots which consume gas without contributing directly to the productive heat transfer process.

3. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 1 Identifying Types of Electronic Ignition Systems Three types of electronic ignition systems will be discussed in this section: (a)Intermittent Spark Ignition (ISI) (b) Direct Spark Ignition (DSI) (c)Hot Surface Ignition (HSI)

4. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPages 1 & 2 In general, each of these systems is made up of the following components that provide these functions: 1.an ignition module that responds to a signal from the gas appliance thermostat provides voltage to 2.an ignition device which serves to start gas combustion; 3.a flame sensing device which produces a flame safety signal sent back to the ignition module, and 4.a gas burner valve which is energized to open by a signal from the ignition module. 5.A lockout device is also part of the system and serves to shut down the appliance if the ignition of the gas cannot be confirmed within a predetermined time.

5. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 2 Always read and follow manufacturer’s instructions for service and installation of system components. Never substitute a component or part that is not a manufacturer’s designated replacement part for the particular appliance being serviced. Electronic ignition modules are not field repairable. Use only factory supplied wiring components specified for use with the particular electronic ignition system being serviced.

6. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 2 Intermittent Spark Ignition Systems Intermittent spark ignition systems use a pilot burner as the ignition device. The pilot burner is not a standing pilot, and therefore is only ignited when the thermostat calls for heat. Figure 1. Typical Ignition Wiring Diagram Identifying Components of an Intermittent Spark Ignition System

7. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 3 Ignition Control Module High Voltage and Risk of Electrical Shock—DO NOT TOUCH OUTPUT TERMINAL. Disconnect power supply before servicing or replacing any connection to an ignition control module. EXPLOSION HAZARD—Turn off gas supply at appliance shutoff valve before servicing.

8. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 3 Figure 2. Ignition Control Module The wiring terminal connections on the module shown are located at the lower edge of the module. Ignition modules respond to the call for heat signal from the thermostat and generate the ignition spark to the pilot assembly and thereafter send power to the pilot valve. The ignition module receives a flame proved signal at the “sense” terminal when the pilot flame is established.

9. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 4 Spark Ignition Pilot Assembly Figure 3. Ignition Pilot Assembly The design of pilot assemblies will vary from manufacturer to manufacturer, but each design provides for a spark electrode, a pilot orifice, burner and hood assembly, and a target electrode for flame rectification. The assembly shown in Figure 3 uses a flame sensor rod as part of the flame rectification circuit. Many ignition control modules provide a “pre purge time” before delivering the spark and gas to the pilot ignition assembly. With these systems there is a short delay between the thermostat call for heat and the time of pilot spark and gas delivery to the pilot assembly.

10. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 4 Gas Valve Figure 4. ISI Control Valve Gas valves used in ISI systems are combination valves. One valve is required for the pilot gas supply—the second valve is required for main burner supply. Each valve must be wired to the proper terminal on the ignition control module.

11. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPages 4 & 5 Operating Sequence Step 1The ignition system reacts to the thermostat “call for heat” by opening the pilot valve and by supplying a spark to the spark electrode on the pilot assembly. (On pre-purge systems the ignition module delays the opening of the pilot valve for the programmed pre-purge time.) [If the pilot does not light, the sequence moves directly to #6.] Step 2After the pilot is lit, an electronic circuit proves the presence of the pilot flame using flame rectification. Step 3A slight delay is provided in the flame sensing circuit to minimize problems due to pilot flame instabilities on ignition. The flame-sensing signal to the ignition control module activates the main burner circuit to the gas control valve, allowing main gas to flow to the burner(s).

12. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 5 Operating Sequence Step 4Sparking continues for a few seconds into the main burner cycle to insure dependable ignition. Step 5In case of flame outage or gas interruption, the flame sensing circuit will shut of main gas flow and then attempt to relight the pilot. Step 6If pilot ignition does not occur within a predetermined length of time, the system will lockout and turn off power to the entire system. Resetting The System After A Lockout. To reactivate the system, on most electronic ignition systems, turn the thermostat to its lowest position for ten seconds and then return it to the desired thermostat setting. Always read and follow manufacturer’s instructions.

13. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 5 Direct Spark Ignition Systems (DSI) Direct Spark Ignition Systems light the main burner without the use of a pilot burner; a spark igniter electrode is placed near the main burner and is the ignition device for the system. Figure 5. Diagram of a Direct Spark Ignition System

14. 7.3.1 Student Book © 2005 Propane Education & Research CouncilPage 6 Figure 6. DSI Ignition Control Module When the burner flame is established, a flame proved signal produced by flame rectification is required to maintain the main burner gas flow, or on high-low burner designs, to open the second stage gas valve for high burner operation. Gas control valves in DSI systems do not have the pilot burner valve used in ISI systems. DSI control valves may be single main burner valves or combination valves that provide multiple burner control or 2-stage burner control in the case of high/low systems.

15. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPages 6 & 7 Operating Sequence Step 1The ignition system reacts to the thermostat “call for heat” by supplying a spark to the spark igniter mounted on the main burner assembly. Step 2The main burner valve is opened to allow gas flow to the burner. Step 3After a burner flame is established, the spark voltage is reduced and the flame sensor generates a flame proved signal by flame rectification. The flame-sensing signal to the ignition control module sustains main burner circuit to the gas control valve, allowing main gas to continue to flow to the burner(s). Step 4If ignition does not occur within a predetermined length of time, the system will lockout and turn off power to the entire system.

16. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 7 Hot Surface Ignition Systems (HSI) Figure 7. Hot Surface Igniter Hot Surface Ignition differs from the spark systems primarily due to its ignition device. Figure 7 illustrates a silicon carbide igniter used in HSI systems The hot element will rapidly heat to temperatures in excess of 2500° F when supplied its operating voltage. This high temperature provides a dependable ignition source which is especially useful in outdoor and roof top furnace applications where lockouts may be a problem for ISI and DSI systems.

17. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 8 Ignition Module Figure 8a. HSI Ignition Control Module Figure 8b. Diagnostic LED Panel The unit is equipped with an LED indicator lamp which signals the system component that is faulty by flashing a trouble code in the event of a component failure.

18. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPage 8 Gas Control Valves HSI control valves must be matched to the ignition system, as is the case of the other electronic ignition systems. The control valve used with a particular appliance will be specified by the manufacturer to provide the proper gas volume and the burner design such as a single rate burner or a two-stage high/low burner system.

19. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPages 6 & 7 Operating Sequence Step 1The ignition system reacts to the thermostat “call for heat” on prepurge systems with a time delay, and on non- prepurge systems, by going directly into an igniter warm up period (typically 30 to 40 seconds). Step 2The main burner valve is opened to allow gas flow to the burner. Depending on the system, the igniter will remain under full power for 2, 4, or 6 seconds during the initial main burner opening cycle.

20. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPages 8 & 9 Operating Sequence Step 3After a burner flame is established, the igniter is de- energized and becomes part of the flame sensor circuit. The flame sensor generates a flame proved signal by flame rectification. The flame-sensing signal to the ignition control module sustains main burner circuit to the gas control valve, allowing main gas to continue to flow to the burner(s). If a flame is not sensed during the initial main burner open cycle the main gas valve is closed. Step 4In a single try system the system will be in lockout after a one-attempt failure. In multiple try systems, the above sequence of ignition attempts will be repeated three times before lockout occurs. EXPLOSION HAZARD—Turn off gas supply at appliance shut off valve before servicing.

21. 7.3.2 Student Book © 2005 Propane Education & Research CouncilPages 9 & 10 Purging air and gas/air mixtures before placing electronic ignition system-equipped appliances into service A word of caution is in order here: Because the appliance may have to be cycled through several lockout and ignition attempts (especially due to the low volume of gas that flows through the pilot burner assembly on ISI systems) technicians are sometimes tempted to vent air and gas/air mixtures near the appliances to speed up the purging of air from the gas distribution lines. This practice may result in injury or property damage. NFPA 54 and other gas safety codes state that the open end of piping systems being purged of gas/air mixtures and gas must not be discharged into confined spaces or areas where ignition sources are present unless precautions are taken to perform this operation in a safe manner by ventilation of the space, control of purging rate, and elimination of all hazardous conditions.

22. 7.3.1 Student Book © 2005 Propane Education & Research CouncilPages 11 - 14 Time to See If You Got the Key Points of This Module… Complete the Review on pages 11 - 13. See if you are ready for the Certification Exam by checking off the performance criteria on page 14.