Why a Noisy Furnace Caused By Delayed Ignition Is a Serious Problem

Mar 30, 2021 | Heating | 0 comments

If you ever experience hearing a loud banging noise coming from your garage or basement, it doesn’t always mean there’s an intruder in the house. That loud banging is probably caused by something called a delayed ignition.

Instead of ignoring it or calling the police, you should contact a 24-hour plumbing service to fix your heating system. It’s best to have it fixed as soon as you can to prevent the problem from escalating. If you’re not sure what to do, here’s what you need to know about delayed ignition and why it happens on your furnace.

What is Delayed Ignition?

When your thermostat calls for heat from your furnace, a gas valve opens, sending gas to the burners inside the furnace where it starts to ignite. Delayed ignition happens when that ignition doesn’t happen immediately, which leads to more buildup of gas. Once there’s too much gas inside that it reaches the flames, it causes a small but thunderous explosion.

What’s Causing it?

There are a couple of possible reasons why delayed ignition happens. All of which need to be resolved with the help of a technician. One probable cause is that there’s too much primary air in the furnace. Primary air is the air mixed with the gas before it ignites. If it gets too much, the gas-air mixture becomes harder to ignite because there’s too much air. That could cause a delay in the ignition.

Another possibility is that there’s too little gas at the burners that the initial ignition gets delayed. The gas-air mixture needs to be just right in order for the ignition to happen. If there’s too much air or too little gas, it’s harder for the gas to ignite.

Finally, leaving your pilot light dirty and restricted could hinder the ignition as well. This happens in older furnaces. Since the pilot light may be too weak due to being clogged by dirt, it would take longer for the gas to ignite.

Why are Delayed Ignitions Costly and Dangerous?

There are literally small explosions happening on your furnace. So, there’s no reason for you to just ignore it. Calling a heating technician or a 24-hour plumbing service should be your priority. Several explosions by the delayed ignition can damage the furnace.

A “flash burn” is also likely to happen. This is when the pilot light gets too weak that you need to reignite it personally. When you do this, there’s a chance that all the extra gas around will ignite while you’re attempting to fix the pilot light yourself. That could only be a bad thing and may even result in severe burns and injuries.

Delayed ignition could also result in the excess flames cracking the furnace’s heat exchanger, which is the most expensive part of the furnace. The worst-case scenario is the fire will roll out of the combustion chamber and result in a house fire.


Hearing loud banging on your furnace is never a good sign. As soon as you hear the sound or notice your furnace acting weird, you need to contact a technician right away. You never know when those little explosions caused by delayed ignition go out of control.

Whenever you have a leaky faucet or a faulty heating system, Emergency Plumbing and Heating is here to help. We have a team of experienced, licensed, and insured contractors providing 24-hour emergency plumbing and heating services to our customers. Call us now for an emergency service request!

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