Key Takeaways
- Direct Spark Ignition Issues: Intermittent flame sensing problems often stem from blocked pilot tubes, weak spark dissipation, or faulty components
- Component Replacement Strategy: When performing heating repairs, replace multiple related components (flame sensor, ignitor, rollout switch) to prevent callbacks
- Spark Testing Method: Test ignitors by holding them near ground with insulated pliers – weak or dissipating sparks indicate ceramic insulation failure
- Critical Environment Considerations: In pharmaceutical or sensitive environments, proactive component replacement provides “inexpensive insurance” against costly failures
This short podcast also covers this burner repair in detail:
The Problem: Intermittent Flame Sensing on a York RTU
This heating tip was generated from some on-site aggravation while repairing a burner. During routine preventative maintenance, I discovered that the York rooftop unit’s (RTU) first-stage burner was having intermittent problems sensing flame and engaging the main fire.
The RTU utilizes direct spark ignition, where the spark is generated, the pilot valve within the gas valve opens, and gas flows across a pilot tube. The flame sensor is mounted at the opposite end of the tube. As the pilot flame moves across the tube and comes into contact with the flame sensor, flame rectification takes place, proving the flame exists.
At this point, the ignition control sends a signal to the gas valve, which engages the main fire. This is how it’s supposed to work in theory, but it’s not always the case. My experience with these burners speaks to me in this particular situation; I have seen this issue many times before.
To learn more about flame rectification and how to properly check flame signals, check out this comprehensive guide on flame rectification.
Common Causes of Ignition Failure
The pilot tube can become blocked and corroded, which can severely restrict proper gas distribution. If the flame sensor can’t sense flame, the main burner will never fire. A defective pilot tube can and will cause persistent burner issues.
The RTU is responsible for heating the northeast corner of a critical environment (pharmaceutical warehouse). The warehouse is outfitted with temperature sensors, and temperature swings can threaten the products stored in the facility. This critical application makes proper preventative maintenance scheduling even more important to avoid costly failures.
The Repair Process
The burner was removed along with the pilot tube, flame sensor, spark ignitor, rollout switch, and ignition module, which were all replaced. I would personally never pull the burner and replace the pilot tube without replacing the flame sensor and ignitor simultaneously.
Why Replace Multiple Components?
I have preached this in the past: anytime I perform a heating repair, I always replace the rollout switch. A rollout switch can be internally faulty, but when checked with a meter, it looks fine on the surface. I’ve encountered many situations like this where the burner wouldn’t fire. The rollout, which appears to be okay, is bypassed with a jumper, and the burner fires immediately.
I also replaced the ignition control as inexpensive insurance to maximize a problem-free heating season due to the critical nature of the environment. The cost of a failure can be significant:
- Quarantined products
- Quality assurance investigations
- Extensive documentation and emails
- Potential product loss
For technicians working with critical systems, understanding BMS control fundamentals can help prevent and diagnose complex control issues before they impact operations.
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Troubleshooting the New Components
After the repair and upon testing, a spark was not being generated. The problem was traced back to the new spark ignitor, which had separated inside the heat shrink. A second new ignitor was then installed, although a problem still existed.
Diagnosing Weak Spark Issues
A weaker than normal spark could be heard coming from the ignitor. I pulled the ignitor assembly from the burner bracket and performed a diagnostic test. If you take the ignitor assembly, hold it with an insulated set of pliers, and hold the rod close to a ground source, you can watch it spark. The test was performed and the spark appeared strong.
The next test revealed the actual problem:
- I tilted the assembly slightly, moving the corner towards ground
- A small, weak spark was visibly noticed
- This should not happen as the ignition rod is fully insulated in a ceramic case
Due to this leak, when the ignitor assembly was mounted, the spark dissipated and was not concentrated and strong enough to light the pilot.
The Solution
As a test, I used electrical tape and wrapped the ignitor bracket to insulate it. After reinstallation, instantly upon testing, the spark was audibly stronger, and the pilot and main burner fired on every attempt.
This type of detailed troubleshooting is essential when working with gas-fired equipment. Always ensure proper carbon monoxide testing procedures are followed after any combustion appliance repair.
Working in critical environments like pharmaceutical warehouses requires exceptional attention to detail and proactive maintenance strategies. Property.com’s ‘Know Before You Go‘ tool helps HVAC professionals prepare for complex commercial jobs by providing detailed property insights and permit history. This preparation is invaluable when servicing critical facilities where downtime costs can be substantial. Learn how Property.com helps HVAC pros elevate their commercial service capabilities.
You can watch the entire repair process in this video:
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