Five Reasons Your Boiler Fails on Ignition

If your boiler is failing to ignite, you are probably in a hurry to figure out why. Boilers are often the most critical piece of commercial equipment a building owns, so we won’t slow you down. Here are the five most common reasons your boiler fails on ignition or pilot.

1. Dirty Flame Scanner

Flame scanners need to be inspected and cleaned frequently, at least once a month. Your flame scanner may operate via UV, visible, or infrared light signaling. However, the result is the same: your flame scanner will sense the energy released by the fire in your furnace.

This flame signal is displayed on your flame safeguard control (optional display screen required), which should be checked daily. The displayed voltage shows the strength of the signal. If this drops over time, it generally means the flame scanner lens needs to be cleaned or the pilot assembly serviced.

However, if your boiler is not igniting and cleaning the scanner lens does not solve the problem, many scanners have a testing function that will allow you to see if it is capable of detecting a flame. An alternative would be to use another source of flame to test for ignition; however, use proper safety protocols when doing this.

2. Cracked or Broken Electrode

Pilot assemblies should be inspected at least every three months and electrodes replaced annually as part of routine maintenance. A cracked or broken electrode will prevent your boiler from igniting and will cause a ticking or clicking noise.

If you notice your boiler working intermittently, then a cracked or broken electrode is not your problem because a boiler with a broken electrode will not work at all. If you do find that your electrode is broken, they are easy to replace, and it will be cheaper to replace it than to try to repair it.

3. Faulty Pilot Ignition Cable

The ignition cable delivers the electrical power to ignite your boiler’s pilot light. This cable works hard and carries a high voltage. You should check pilot ignition cables at least every three months to ensure they are firmly connected. Also, check for any cracks, which could sever the connection or allow it to ground out early. Regardless of any faults, these cables should be replaced annually as part of your routine maintenance schedule.

4. Defective Pilot Ignition Transformer

Pilot ignition transformers are maintenance-free and can last several years, but their life can be shortened by faulty cables. Pilot ignition transformers work differently than the open flame pilot lights used in older systems, but they are still a vital part of your heating system, and your boiler will not work without them. Yet, they are a frequent cause of boiler malfunctions.

Ignitors work in a couple of different ways to start the boiler when the thermostat triggers it. One type makes a spark that ignites the gas your heater uses. The other type heats up to ignite the gas, which then heats the air blowing from your boiler.

There are some signs that indicate your ignitor is broken or could be going bad:

  • The boiler’s air blower stops.
  • Your boiler frequently starts and stops, indicating that it is not holding a charge.
  • The boiler repeatedly trips your breaker immediately after the air starts blowing.
  • You hear your boiler click, but it doesn’t start. If this happens, you may have a dangerous problem with your ignitor.

If you notice any of these problems, you need to have a professional check your boiler. But the good news is that you can replace an ignitor rather than having to buy a new boiler.

5. Closed Pilot Valve

Did someone accidentally close the manual gas valve for the pilot? The valve needs to be open for gas to reach your boiler. This may seem like an unlikely reason for your problem, but it’s worth a look. Maybe one of your employees turned it off for safety reasons and forgot to turn it back on.


Your boiler failing on ignition is a serious problem, but don’t panic. As you can see, any of these problems can be fixed. So stay calm and consider whether your boiler may be suffering from any of these problems. If the problem doesn’t seem easy to solve, don’t hesitate to call for help.

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