All About Ignitors

*Please Note: These tests and procedures are to be performed by a qualified technician only*

Fall is here and winter is just around the corner. Ensuring your heater is ready to go and working properly is a top priority before the first frost comes. Checking every component of your heating system and starting it up a few weeks before you think you’ll need to. Arguably the most delicate part of your heater and the heating system is the ignitor. The ignitor is responsible for lighting the gas released from the gas valve and, causes it to ignite into a flame. When you turn up your thermostat, that initiates a call for heat to the heater. This will tell the ignition control model to start the trial for ignition. The blower will be the next component to turn on. The blower will create a difference in air pressure and will close the air pressure switch. If this sequence of the heating cycle was successful, then the ignitor to either spark or glow.

There are two major types of ignitors, a direct spark and a glow bar ignitor. Depending on the voltage supplied to your heater, your ignitor could have anywhere from 80-240 volts running to it. An igniter that is cleaned regularly and isn’t often exposed to excess gas and heat will last an average of 3-7 years.

A direct spark ignitor generates an electrical current between the two metal rods when there is a call for heat. When the gas valve opens to release gas, the gas will become ignited by the spark and lite the burners.

A hot surface ignitor turns from black to red as it heats up and quite literally glows. They are made of silicon carbide and are extremely fragile. After the igniter is switched off and the boiler continues to run, the igniter functions as a flame sensor for the boiler control.

So what can cause an ignitor to fail or stop working?

The most common reason is that they will break. As mentioned earlier, the filament on ignitors are EXTREMELY fragile and can break if they are put down the wrong way or if too much pressure is applied to them, so be very careful when handling them. The filament on the ignitors also receive a great amount of pressure and heat from the gas being pushed out of the gas valve and onto them, which can cause a lot of damage.

It could also stop working if it is getting the incorrect voltage supplied to it. Too low of a voltage can cause the igniter to not get hot enough and will not ignite the gas when the gas valve opens. Too high of a voltage can be too much electricity for the igniter to handle and will cause the ignitor to break. This voltage can also possibly travel all the way back through the wires and potenitally burn-out the control board as well.

Overuse. The more you use something, the faster it’s going to wear out. If you have a faulty control board or ignition control module that tells the ignitor to glow or spark for longer than it has to, then it will shorten the lifespan of the ignitor dramatically. As stated earlier, an ignitor does not benefit from excess gas or heat being thrown its way. In addition, when the heat exchanger runs longer than it should and gives off excess heat, it can damage the ignitor and its ceramic base.

Your ignitor is dirty. Ignitors can easily be covered in dirt, carbon deposits, or falling rust from the heater (especially on ignitors that are horizontal). A dirty igniter will not heat up as fast or nearly as hot, which could be the reason the gas will not ignite.

To test an ignitor to see if it is working properly, you can test it two ways.

Look into your furnace and see if the igniter glows or sparks when there is a call for heat. If your heater goes into lock-out after the trial for ignition, that is a good indicator that the igniter is bad.

Use an ohm meter set to the lowest setting for resistance, or resistance with tone if your ohm meter has the option. Shut off power to your heater and access the terminals inside the ignitor plug, being sure not to touch the filament. Use the leads to measure resistance against each of the terminals within the plug. You should get a reading between 50 and 400 ohms – this ensures the ignitor has continuity. If you get a reading under 50 or close to zero, then the ignitor has burned out and needs to be replaced.