Furnace Parts – What do they do?

Furnace parts, am I right?

If your heat has stopped working, started to make a strange noise, or if your furnace has started grinding, or gone BANG! Then you’ve called for help. After a thorough diagnosis your brilliant R&B technician has announced what the problem is… and you’re still left wondering, what did he say that was again? How did it break? Why did it fail, and most importantly, why did two parts fail at the same time?
Aside from the most common questions such as…
What will it cost? And,
How long will it take?

…which often can’t be answered, we can answer the question of what it does. Many parts work closely together and the failure of one is the result of the failure of another. Here for your reference are some common furnace and boiler terms and definitions for you.

Heating terms and definitions:

Gas valve – This part will open or close as the system calls for heat so as to provide gas flow for combustion. It also serves to reduce the gas pressure coming in to the heating unit. Just as with a car the air / fuel mix needs to be just right for the combustion to occur and to happen efficiently. Sometimes these parts will fail and not reduce the gas enough, or not open or close, as they should.

Igniter – An igniter is a lot like an incandescent light bulb in that it gets hot and glows. These are often referred to as hot surface igniters because the thin wire receives an electrical current when the furnace calls for heat and the end gets red hot to ignite the gas and start the heating. These wear out!

Flame rod sensor – If it were called a flame sensor rod we’d know what it was! The flame rod sensor, so named by a lovely dyslexic heating master has one simple function and that is to sense if there is a flame present when the gas is turned on. If the gas did not ignite, it would seep into the living space of the home and endanger the occupants. These need to be cleaned at your annual heating appliance service because if they aren’t clean, they can’t sense.

Thermocouple – A common failure in older furnaces and as a relatively inexpensive part may be replaced pro-actively with your annual service. Its function is to shut off the gas if the pilot light goes out and the igniter fails to re-light the furnace.

Pilot assembly – A pilot assembly is made up of the pilot, the igniter and the thermocouple. It is typically replaced in its entirety if there is corrosion on the pilot and it can’t be cleaned.

Pressure switches – These little safety switches are activated when excess pressure in your system pushes on them. When gas or fluid pressure changes (either too high or too low to be safe) the movement of the pressure switch will control the electrical current to turn things off.

High limit Switches – These are actually sensors that are designed to ‘trip’ or switch the furnace off. Their function acts as a safety measure in case the furnace overheats. A common cause of overheating is if the airflow is somehow restricted. Then the furnace will continually cycle on and off and overheat. If you find that your furnace is coming on but not actually staying on long enough to warm up the house, this could be the issue. Although, it could also be the restricted air flow!

Manifold of Burners – The manifold is the row or area where the burners sit. The burners are the actual place where the flame comes out to create heat. These can collect black carbon build up if not maintained and that causes the metal to corrode and become brittle. Once that happens those nice little burn holes become misshapen and the air gas ratio is even works and the heating becomes uneven and inefficiency. The incomplete combustion will lead to even more problems.

Blower motor – For your gas furnace just as it sounds, this part is used to blow the heated air through the ducting of your home. When air circulation is limited, or non-existent your blower motor may have failed. If your blower motor is making noise, it can be due to a lack of lubrication and can seize up completely. Your annual furnace maintenance should include the lubrication of the blower bearing assembly to prevent the pre-mature wear and failure of this heating part. When this part fails, the furnace may turn on, but then trip out on a high limit as the lack of air flow causes it to overheat.

Heat exchanger (Primary) – The primary (first in line) exchanger is really a collection of several parts that make up a whole unit. The job of this unit is to heat the air (or water) generated from process of combustion, while to keeping toxic exhaust carbon monoxide separate from living space. It allows the heat from exhaust air to be absorbed by clean air and circulated throughout your home.

The term exchanger refers to the idea of exchanging the heat for the cold as the exhaust leaves the venting. These can plug or crack or corrode if a furnace is getting water in it from improper condensation management. Anything that interferes with the safe containment of the carbon monoxide is cause for the immediate and emergency shut down of the appliance.

Secondary heat exchanger – Found on higher efficiency furnaces this is a second step in the heating process that uses the residual heat in the exhaust air as it condenses. The action of the water vapor turning to liquid allows the furnace to capture the maximum amount of heat from the exhaust air as it leaves the furnace.

Inducer motor – Controlling the air that moves through the heat exchanger, this motor “induces” a draft that draws the exhaust air through the heat exchanger and towards the outside of the home. They will wear out over time, and typically start to make noise when they do. No inducer motor equals no heat!

Condensate pump – As the exhaust air vents out of your home, it cools and creates condensation. That condensation is collected in a little box the size of a shoebox but not nearly as exciting. If your furnace is installed below grade, that water will get pumped up and out of your home. Sometimes these boxes crack or the pumps fail and need to be replaced. If your condensate pump or drain line has failed you will often see a little puddle of water beside your furnace. Condensate lines need to be cleared and maintained and are a part of the work done at your annual service. Clogged lines can back up into your furnace and cause corrosion or electrical shortages.

Zone valve – These are used on hydronic/ hot water heating systems to control the water flow to certain areas of the home when the call for heat is turned on or off. Each thermostat will activate it’s own zone. As these are activated and have moving parts they do wear out. Commonly when there is no heat in a certain zone but others are working well, we look to the zone valve as the culprit.

Expansion tank – In a closed system where there is water being heated, the expansion tank allows for the thermal expansion of the water by absorbing it within the tank. Over time, the air cushion that is displaced by the water expansion fails and the tank is just full of water. This is referred to as the tank being water logged. When this happens your technician will typically recommend the replacement. Keeping the pressure at correct levels in your hot water system will prevent failures in the system or the release of water from a pressure relief valve onto the floor.

Plumbing code does required that expansion tanks are installed with gas fired hot water tanks, or water heaters, but we often see in older installations that they haven’t been.

I hope that you’ve found this smattering of terms and parts to be helpful. For further information or specific diagnostics on your heating issue, please call R&B and we will help.