Five Reasons Your Gas Boiler Fails on Ignition

If your gas 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, whether you have an oil burner or gas burner. Your flame scanner may operate via UV, visible, or infrared light signaling. However, the result of all of these is the same: your flame scanner will sense the energy released by the fire in the combustion chamber of your furnace, and if it does not detect it, the oil or gas boiler will cut off the gas supply.

In most cases, the flame signal will be 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 not firing 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 both pilot and flame failure electrodes should be inspected and replaced annually as part of routine maintenance. A cracked or broken pilot 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 them than to try to repair them.

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 which will pass through flame rectification to a properly grounded burner assembly. If your boiler does not seem to be attempting to ignite, check to ensure it has power, and if not, inspect the fuse box to see if any fuse has tripped. You should inspect 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, which could explain any tripped fuses. 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. Faulty Gas Valve Pilot Valve

Most modern boilers are gas appliances which means that they are powered by natural gas or propane. In order for your boiler to function, the gas supply must be able to reach your system. This is the job of the gas valve to regulate the flow and allow it to safely and efficiently provide your home with heating and hot water when it is needed. Under normal operating conditions, this valve will open and close based on demand. For example, if your thermostat is set to heat up your home or you take a long hot shower, the valve will open up to provide the boiler with more heat. These are vitally important components, and when something goes wrong such as a blockage in the valve, a seized part, or a damaged electrical component, your system may fail to ignite.

In most cases, these issues are easy to solve, but as a gas appliance, these systems must be worked on by an authorized and regulated professional. If improperly repaired, these systems can release gases such as carbon monoxide leading to damages to your system, injuries, and even death.

However, before assuming that your boiler’s gas valve is at fault, make sure to check your 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. A quick check can normally determine if this is the case and if so, opening the valve and resetting your boiler will likely solve the problem and have your system back in working order in no time.


Your boiler failing on ignition is a serious problem, especially if it is winter and your business is without central heating. 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 from a gas safe engineer. If your high efficiency boiler is kept in good repair, it will be more energy efficient.

Michael Bendjouya

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