Issue:
Won't light or won't sense the pilot - what to look for (IntelliPak 20-130 w/ Legacy Controls only)
Resolution:
Refer to SZ-SB-55
Notes:
Verify that unit inlet pressure is 6" to 8" (NG).
Verify that the pilot pressure is between 2" and 3". If the pressure is lower or higher, dismantle the pilot line and look for restrictions.
The damper stop bolt on the combustion damper should be set at 0.5" to 1.0" higher than the 100% firing position.
Try the above first, then check the basics:
Incoming gas pressure must be between 7" and 14" when the unit is on full fire.
The proper burner sequence is:
Combustion blower and Honeywell control get power at the same time.
The Honeywell control sits idle during the approximate 60 second pre-purge.
The pilot output and igniter get power for 10 seconds.
If the Honeywell control sees a flame signal (flame LED on) at the end of 10 second proving period then the main burner ignites.
If the Honeywell control does not see a flame signal (flame LED off) at the end of the 10 second proving period then the control locks out and the alarm
LED comes on.
How to troubleshoot:
Measure pilot line pressure - typical good pressure is 2"-2.5" ;
If pressure is higher, there is likely a restriction in the downstream pilot shutoff valve or the welded pilot line connection.
If pressure is lower and adjusting the pilot regulator does not help, there is likely a restriction in the upstream pilot shutoff valve or pilot assembly.
Measure the AC voltage at 4TB15-11 to ground during the pre-purge sequence - it can be anywhere from 130 to 220 VAC. This is a very low current circuit so the type of meter used will affect what reading is seen on any given unit. When the pilot lights, the voltage will fluctuate, then drop by about 10-15 volts.
If the voltage does not drop, the flame is not touching the flame sensor - this indicates that the pilot gas volume is insufficient.
If the voltage does drop, the Honeywell control is not seeing the signal. Test the Amplifier.
Note: When you measure AC voltage the Honeywell control cannot sense a flame (your meter affects the circuit) so be sure to try the burner without a meter connected anytime a change is made.
How to test the Amplifier: During a trial for ignition measure the DC voltage at the Honeywell control + and - terminals. If at least 1.5 VDC is seen yet the flame LED does not come on, replace the Amplifier.
Here is another way to test the amplifier circuit:
Just to the left of the Honeywell control is a green ground wire #199A. Remove the screw connecting the wire to the chassis and connect a DC Microampere meter in series between the green wire and the chassis of the unit. Test the unit in heating - when the pilot is lit, a reading should be seen.
If the signal is between 1 and 10 microamps and steady, the amplifier is not reading the signal and is likely bad.
If the signal is less than 1 microamp or is fluctuating badly, the flame sensor is not fully in the flame. Look for a gas flow / air flow issue.
If the above checks out, start looking for wrong parts, wrong orifice depth and all of the other issues mentioned above.
Here is a list of problems that we have heard about or discovered in the last several months that could cause a unit to not sense a flame during the pilot sequence.
COMBUSTION AIR PROBLEMS
Combustion blower inlet orifice opening should be approx 5" on 850MBH (all) and 500MBH 2 stage.
Combustion blower inlet orifice opening should be approx 3.5" on 500MBH modulating heat
Combustion fan for modulating heat units should be on high speed for 850 and low speed for 500
The combustion air duct blockoff (drawing below) should be secured snug to the duct wall and in a horizontal plane.
This blockoff can be seen by removing the burner sightglass plate and looking down the duct opening.
FLAME SENSING CONNECTION PROBLEMS
The flame rod (4U19) nut should be snug against the wire terminal (200B).
The green ground wire (199A) from the IGN control should be securely fastened to t.he ground screw
PILOT LINE NOT ALLOWING SUFFICIENT VOLUME OF PILOT GAS
The pilot line components may be partially plugged with grease, pipe dope, or metal shavings.
A 5/16" drill should fit through each of the brass shutoff valves - look for an improperly drilled opening.
Completely dismantle the pilot assembly and inspect each part for partial restriction
Where the pilot line is welded to the main gas inlet, verify that there is no weld slag partially blocking the opening (stick a 5/16" drill through it)
See drawing below for the pilot line weld location
GAS TRAIN ISSUES
Improper orifice - 850 MBH should have an H orifice, 500MBH should have #21 orifice.
Orifice too far in or out: The distance from the welded stop to the outer edge of the orifice should be 7 1/8" (see drawing in SZ-SB-55)
BURNER PARTS:
Diffuser plate (perforated) should be 5.6" diameter rather than 10.5".
The correct diffuser is flat, the incorrect diffuser is shaped like a pie pan.
Other Question/Problem/Cause Statements:
- Won't light or won't sense the pilot - what to look for (IntelliPak 20-130 only)
- Unit will not sense the flame
- Gas heat flame sensing issue
- Gas heat will not stay lit
WARNING:
Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.