Part 1 (from May/Jun Indoor Comfort)
This discussion will give some direct application of procedures for troubleshooting hot surface ignition controls. It will not address their use with integrated boiler or furnace controls.
Figure 1 is an example of a very simple application of hot surface ignition using silicon carbide igniters. We will address silicon nitride igniters later in this discussion.
The two igniters from Norton in Table 1 point out the various characteristics of the different igniters they produce. The emphasis here will be on the heating application only using the Norton 201 and 271 igniters, which are 120-volt igniters that have been used extensively for a number of years. Norton introduced mini-igniters in 1988 and my first contact with them was in 1993.
The Norton 401, 24-volt igniter is used with Honeywell Smart Valve Generation I, II and III (SV9540 and SV9640). With the advent of Honeywell Generation III, we see the Norton 601 igniter, which is a 120-volt igniter, used with Smart Valve SV9510/9520 and SV9610/9620.
The Norton 401, 24 volts has a very short warmup time (three seconds) due to it being a silicon-nitride material. It has a low resistance to cold (1–4 ohms) and therefore heats up much more quickly than standard 120-volt silicon-carbide igniters. The Norton 601, 120-
volt igniter also has a short warm-up time (five seconds) with a cold resistance of 50–300 ohms. It should be mentioned here that Norton (Coorstek) also makes Gas Dryer Igniters (the 101) and Gas Range Igniters (the 501).
The igniters shown in Figure 2 are all model 271 17-second warmup time igniters from Norton. The exception is the igniter on the lower right-hand side—the 41-413—which is the igniter used by Carlin for its G3A and G3B power gas conversion burners. It is a 34-second igniter. As you observe the different igniters, the main difference is not the igniter portion itself; they are all basically the same. What is different is the ceramic connector and wiring harness. The wiring harnesses can be cut and wire nuts used if necessary to do so.
Hot Surface Operation
The silicon carbide element can be handled without damage; however, it is better and safer to handle the igniter by the ceramic holder. The myth that the silicon carbide tip cannot be handled because body oils cause contamination is untrue.
On a typical heating system with hot surface ignition, a call for heat (thermostat contacts closed) will send a 24-volt signal to the igniter module. When energized, the module will power-up the igniter. If the module is a pre-purge model, it will delay 15 or 30 seconds before the igniter is activated. On pre-purge models, the module will energize the combustion blower or other relays at the beginning of the cycle.
Once the pre-purge timing is up (if so equipped), the silicon carbide igniter heats up to proper ignition temperature (above 1,800°F) in either 17 or 34 seconds, 20 or 40 seconds for some models, depending on the manufacturer of the module. NOTE: A 17- or 20-second igniter can be used on a 34- or 40-second application, but you could not use a 17- or 20-second module with a 34- or 40-second igniter.
It should be noted here that the igniters are made by Norton (now Coorstek), Carborundum (now Surface Igniter Corp.), Igniter Systems Inc. and some other small companies. For purposes of replacement, the Norton Igniters are distributed by Robertshaw. See 41-400 series for replacement. White Rodgers has its own line of igniters (the 767A series).
At the end of the igniter warm-up period, the gas valve main valve opens. The igniter will remain on for a specific amount of time (seconds) depending on the specific ignition module being used. This “ON” time, or trial for ignition time, can vary depending on the specific ignition module being used. When main burner ignition occurs, the flame is sensed by the igniter (local sense) or by a remote sensor (remote sense). With main burner flame established, the igniter is turned off (120 volts is shut-off to igniter).
NOTE: The burner flame must be detected within the timed trial for ignition. If no flame is detected, the gas main valve is de-energized, shutting off the gas flow. The system may go into lockout, or if it has retry model, it will retry the number of times allocated.
Hot Surface Ignition issues
In some respects, Hot Surface Ignition (HSI) troubleshooting is somewhat more complicated; Figure 3 illustrates this.
• It is not always clear whether you are looking at a pre-purge period or an igniter warm-up period.
• Some of the sequences of operation used with HSI are really complex; if you don’t know what to look for, you may falsely conclude that it is faulty.
• Ignition trials are very short (a few seconds), so sometimes you may have to make measurements fast.
Some preliminary checks can be made on HSI systems that will many times find the problem. The four basic questions that follow can many times pinpoint the problem (see Figures 4-8).
Hot Surface Ignition Troubleshooting
The troubleshooting procedures that follow are more detailed and cover each problem, possible cause, solutions and procedures.
PROBLEM #1: Hot Surface Igniter Does Not Glow Remember to wait for pre-purge time (on models so equipped). Possible causes:
• No main power
• Faulty transformer
• Faulty thermostat
• Faulty limit switch
• Faulty blower interlock switch (pressure switch, combustion blower proving switch)
• Faulty hot surface igniter
• Faulty ignition control or integrated control
Perform normal system checks of main power, secondary of transformer, etc. With power on and thermostat calling, check voltage at 24V or TH to 24V ground at the module or integrated control. If no 24 volts, check the transformer. Also check other controls in the circuit from transformer to module or integrated control. Check for 120 volts from (L1) to Neutral (L2), check for 120 volts from “IGN” TO “IGN” or on some modules from the HSI terminals. If you have 24 volts to module or integrated control and 120 volts and no 120 or 24 volts out of the module or integrated control, the module or control is faulty. Check the amperage draw of igniter with AMP meter or AMPROBE amperage; it should not exceed 4.75 amps.
1. Perform a visual check of the igniter for signs of damage or cracks. The sleeving over the wire should be examined for chafing, burned portions or cuts in the wire. The connectors should be properly seated and free from oxidation and/or corrosion. Look for “hot spots” on the igniter, as in Figure 9. Also pull on the wires to make sure they have not become disconnected inside the ceramic holder. Observe the igniter during heat up. If a bright, white line across one of the igniter legs is detected, a crack may exist that could cause premature failure. Allow the igniter to cool and perform a resistance test. Additional signs of a crack are an “open” igniter (that shows no continuity when tested) or a buildup of white silica dust around the bright spot. Replace the igniter if you see these cracks.
2. There are several possible causes for repeated igniter failures—one would be high supply voltage. Hot surface igniters can burn out at approximately 132 volts. Even voltages in excess of 125 volts may reduce igniter life. If high voltage is present, request the power company lowers the power.
3. Other causes for igniter failure include drywall dust, fiberglass insulation, sealants or other contaminants that may accumulate on the igniter. In some cases condensate dripping on the igniter causes it to fail. Some sort of protection above the igniter will prevent this from happening again.
4. Furnace or boiler short-cycling, delayed ignition or an over-gassed condition are also contributors to shortened igniter life.
Perform a resistance test on the igniter
The manufacturer recommends performing a simple room temperature resistance (RTR) test after installing the igniter (remember to disconnect the leads to ensure that only the resistance of the igniter is measured). If the RTR is not to specification as shown in Table 1 for igniter Model 201, which is a 34-second warmup time igniter of 45–400 ohms, or the igniter Model 271, which is a 17-second warmup time igniter of 40–75 ohms, then the silicone tip is damaged in some way and should be replaced. When troubleshooting an appliance where the igniter is suspect, the RTR will be higher on a used igniter; the resistance should be no more than double the original resistance at installation. The 201 is 90–800 ohms; the 271 is 80–150 ohms.
PROBLEM #2: Igniter Glows but Main Burner Will Not Light
• Improper igniter alignment
• Faulty ignition control
• Faulty gas valve
• High inlet pressure (LP gas)
• Polarity reversed
• No earth ground
Make sure gas is available at gas valve. Too high pressure will lock-up the gas valve. Check and make sure polarity is correct. Make sure the igniter is in position (you cannot move the igniter from its designed position). Check for a good earth ground from L1 to the furnace chassis—you should read 120 volts; if not, check and or repair ignition ground wire or ignition control mounting screws. A jumper from ground to gas line should give a good ground. Check for 24 volts to gas valve; if yes and valve does not open, replace valve; if no, replace ignition module.
1. If the igniter is going to be used as a sensor, then make sure the flame is capable of providing a good rectification signal. Make sure that about 3/4″ to 1″ of the flame sensor or igniter sensor is continuously immersed in the flame for the best flame signal. Bend the bracket or the flame sensor and/or relocate the sensor as necessary. Do not relocate an igniter or combination igniter-sensor.
2. Check for excessive (over 1,000°F or 538°C) temperature at the ceramic insulator on the flame sensor. Excessive temperature can cause a short to ground; move the sensor to a cooler location or shield the insulator. Do not relocate an igniter or combination ignitersensor.
3. Check for cracked ceramic insulator, which can cause a short to ground, and replace the sensor if necessary.
a. Make sure that the electrical connections are clean and tight. Replace damaged wire with moisture-resistant No. 18 wire rated for continuous duty up to 105°C (221°F).
PROBLEM# 3: Main Burner Shuts Off Before the Thermostat is Satisfied
• Improper igniter alignment
• Faulty ignition control
• Contaminated igniter and/or sensor (remote senses)
• Bad burner ground
Check for proper polarity. Check for proper igniter position; make sure proper ignition control is grounded. Check for foreign matter on igniter or sensor. Clean or replace. Check main burner ground by checking continuity between ground and burner. If previous checks are okay, you may need to check the microamps on the system.
Part 2 (from Jul/Aug Indoor Comfort)
When checking the flame signal, it is important to realize that when a hot surface igniter (HSI) is also being used as a sensor, there will be some difficulty in checking the micro-amps. There are several procedures you can follow. In my opinion, the procedure in Figure 1 is the preferred method. It is also important to note the technical bulletin from Norton (Coorstek) points out that the igniter can have a buildup of oxide that can cause it to be a poor sensor.
It has been my observation that when the igniter is used on atmospheric burners, exposing the igniter to whatever contaminants are in the room, the igniter is a poor sensor. Atmospheric burners tend to work a little better when the igniter is used in a sealed combustion chamber that gets its air for combustion from the outdoors.
Direct Sense: The Igniter as a Flame Rod
Sensing through flame rectification, whether “direct” (through the igniter) or “remote” (separate flame rod), involves certain components and variables. The object is to use the ionized particles in the flame (burning gas) to conduct a current and complete an electrical circuit.
The control module initiates an AC signal that is sent out to the igniter. The flame acts as a diode and converts the AC signal to a rectified DC signal. The strength of the signal required to prove flame, and therefore keep the gas valve open, is dependent on the control module and varies from one control manufacturer’s board to another.
Signal strength can be affected by:
• the type of burner,
• the position of the igniter in the flame,
• the age of the igniter,
• the type of gas,
• coating on the igniter and
• any impurities that build up on the system over time.
It is imperative that the flame remains in contact with the burner, and that the burner and control module have the same common ground.
When using the igniter as the sense unit, it is important to remember that as an igniter ages, a thin oxide (Si02) layer is formed on the surface. This is part of the normal aging process of a silicon carbide igniter. As this oxide layer is formed, it actually helps seal the underlying SiC grains and inhibits further rapid oxidation. The silica (silicon oxide) that has formed is a glass, which is an insulator and will diminish the strength of the flame signal that is being sent out. Whether the signal will still be strong enough to keep the valve open as the igniter ages is application-dependent.
Although direct sense can be a very feasible alternative, in the final analysis, it is the responsibility of the Original Equipment Manufacturer’s (OEM) testing to determine if it is a viable solution for the particular application.
Checking microamps with systems using the igniter as a sensor can sometimes be difficult. The problem is distinguishing between the 120 volts AC (VAC) power to get the igniter to glow and then reading the microamps created by the flame to igniter/sensor using the equipment burner as ground.
Figure 1 (previous page) was developed by the author of this article. It includes a list of parts needed to make the switch tester and the wiring to get the switch to work. Figure 3 shows microamp check with a separate sensor.
Hot Surface Igniters Replacements
The distributor for Norton (Coorstek) Igniters is Robertshaw Controls Co. They can be found in the latest Robertshaw Catalogs under the Uni-Line 41-400 catalog series for the Norton (Coorstek) 201 and 271 igniters. It should be pointed out that the igniters that are offered in the catalog are all 17-second warm-up time igniters (Norton 271) with one exception, which is the Norton 201 C (Robertshaw 41-413) used on the Carlin Gas Conversion burner only.
The Mini-igniters from Norton (Norton 601 series) are carried under the Robertshaw catalog series 41-600.
It should be noted that the basic difference between igniters is the ceramic base and the mounting brackets. This makes for some difficulty in using them interchangeably and this is not recommended. It is possible that the mated plug on the lead wires may not match up with the unit being replaced. In that case, the wires can be cut and wire nuts can be used to join the wires.
White Rodgers Control Co. also offers Silicon Carbide Igniters in its F767A series. It should be noted that items in the White Rodgers modules 50E47 series require a special wiring harness as shown in Figure 4.
When replacing White Rodgers with another module system, it requires a wiring change using the special adapter shown in Figure 4, which is included in all the universal module replacement kits, such as Honeywell S8910U.
One of the most helpful things to understand is that these igniters can be cross-referenced with one another in Figure 2 (see page 12). Figure 5 (see page 15) describes White-Rodgers’ silicon carbide HSIs in more depth.
There are several upgrade kits offered by the various manufacturers whose purpose is to convert from a Silicon Carbide Igniter over to a Silicon Nitride Igniter. White Rodgers offers the 21D64-2 Nitride Upgrade Kit. This kit does not need an extra module as the now obsolete 21D64-1 required. You can use the old module to change the igniter.
Honeywell supplies the Q3200U Universal Hot Surface Igniter Kit, designed to provide a robust field service replacement igniter in gas-fired appliances with Norton/St Gobain (Coorstek) 120 VAC silicon carbide HSIs. The Q3200U uses a 120-volt silicon nitride igniter design with long life and high resistance to damage or burnout in the appliance. The kit includes the specially-designed silicon nitride igniter and six different bracket configurations to adapt the igniter to the specific appliance application along with accessory parts to mount and wire the igniter. Clear instructions and application templates are provided to simplify selection of the proper bracket and ease installation of the replacement.
Robertshaw also offers the 41-400N Series, which is a collection of Silicon Nitride Igniters. They are produced by Kyocera and distributed through Robertshaw.
Also from Kyocera and distributed by Robertshaw are the 41-801N, 41-802N and the 41- 803. It is very important to note that these three igniters cannot be used as a flame sensor. A separate flame rod is required, such as Robertshaw 1751-729 (24″ lead) or 1751-749 (72″ lead).
This concludes the two-part presentation on Hot Surface Ignition Troubleshooting. We will cover Universal Electronic Ignition Gas Valves in the next article. ICM
Timmie M. McElwain is President of Gas Appliance Service, which provides training for those servicing gas combustion equipment. He is a certified instructor and test proctor for the Propane Gas Association in their CETP program.