The
gas burner goes on, then off. The
gas burner goes on, then off.
Stop getting sicker This is the most frequent question in the heating season HVAC DIY sites, as it is a universal problem with flame sensors.
Did you do the tasks recommended in the manufacturer's Owner's Manual?
Take about 15 minutes or so to find, clean the sensor.
If this doesn't take care of it, call the pro.
This is the most usual
cause, which also means it is not the only possible cause. This is something you
might be able to do, which is not the same as saying you'd be able to adjust the
gas pressure or read the exhaust pressure with delicate instruments that you
don't have or know how to use. As for YOU adjusting it - nobody anywhere
outside they who've known you can tell if you can adjust a burner without
blowing the room apart or burning the house some hours later.
You would
do what an experienced tech would do:
Use instruments to tell if the gas
pressure is correct according to manufacturer specs, and check the air flow to
see if the right amount of air is flowing through the furnace to take the heat
to the house. You'd also check to see if the furnace is operating correctly and
the ducts aren't apart.
If you haven't taken the factory gas furnace
course or at least a vocational course that the tech should have taken, then you
have a steep learning curve to 'catch up' to the years of experience needed to
do it safely. Please don't ask someone to give you the vocational training over
the net by an unsupervised correspondence course.
Another frequent problem is that the lower tube attached to the pressure
sensor
gathers moisture
and has to be removed, blown clear of moisture, replaced. This water block of a few drops
of
water stops the flame sequence similarly to the dirty flame sensor.
Why do you have this problem?
ALL systems MUST have a sensor to confirm that there is a flame to continue for any time. The spark-to-burner and the hot surface ignitor are types of ignition systems that have NO pilot AT ALL they prove flame by a current between the main burner and their sensor. Other ignition systems light a pilot first and check there is a pilot flame before they allow the main burner to get gas to light. If the sensor does not sense the pilot or main burner flame that you have lit because it is dirty or broken, you don't get the burner to remain lit.
It is a predictable occurance, as the atmosphere contains chemicals and dusts that coat and affect the sensor. Thus the manufacturer recommends in the literature that comes with each new furnace to have yearly service procedures to test the furnace gas and draft pressure, make sure it is as clean as when it came from the factory, clean or replace the sensor, clean and tighten all connections and test it for reliable operation. Cleaning and tightening all other contacts, fastons, molex conectors and ground screws is part of an annual service contract (or at least should be done.) You probably didn't have this done as most are used to the old standing pilot furnaces that didn't have to have this done to light reliably for years.
Chlorine, sulphur and other chemical compounds, especially in laundry rooms, coat the sensor and other electrical contacts, so create a resistance to the current. Cleaning the sensor with a dollar bill or other scrub surface that will not leave a wire (steel wool is a culprit) to short out the sensor to ground might restore the sensor. If not, replace it.
You can find the sensor by following a small wire from the ignition module box to the sensor near the burner.
A useful practice is to keep a new sensor on hand and learn to replace it in the fall before the season starts. That could be a regular practice of a service company. Although the incentive is lessened considerably by being able to keep busy and wealthy all winter just cleaning or replacing sensors, there really isn't usually much more to do than to complete the service checks in the factory procedure sheet..
Some heaters use a hot surface ignitor made of brittle material. There are hot surface ignitions that use the ignitor as a flame sensor, so don't show a separate sensor like that above.
Hot Surface Ignitor
The ignitor might break, so must be replaced. When replacing, do not handle the ignitor as oils from the hand can make hot spots to stress crack them as they glow. Sometimes, a shield would be needed to cover them from dripping condensation.
Others use a spark to ignite the gas. Hot surface or spark ignition systems usually have a sensor.
Whichever is used, there is a sensor to check if the flame is there.
On older systems and some newer systems thermocouples
are the sensors of standing-pilot heaters.
If you have other
problems:
Give a good and unusual start by actually saying the
make and model to a service company right way, as you know that there isn't
just the one heater you have in the world.
In other words, be prudent and
safe and call a qualified gas technician as instructed in your furnace
owner's manual.