The Vacuum Pressure Switch

If you own an Austroflamm Wega or an older Integra, Breckwell, Whitfield, Englander, Lopi, Quadrafire, Avalon, and I’m sure several other Pelletstove brands that I’ve neglected to mention, you have a vacuum pressure switch. As a matter of fact, some Englanders have two vacuum pressure switches.

Whitfield Insert picture #5

The switch is easily identified because it is connected to hose or tube of about 1/4″ diameter that runs to the exhaust fan housing or somewhere on the stove body that communicates to typically a negative pressure environment created by the exhaust fan. The idea here is that the exhaust fan, downstream of the burnpot, is “sucking” the smoke, heat, and particulate created by the burning pellets, in turn, fresh air is drawn through the holes in the burnpot providing the oxygen and turbulence required for a continued efficient fire. There is a diaphragm located within the vacuum pressure switch, as long as the exhaust fan is doing its thing and the required minimum negative pressure is maintained, the diaphragm is pulled closing the switch allowing electricity will travel across it. The switch is hooked up to the auger motor. So, if the exhaust fan fails or the stove door is left open the auger motor should stop feeding pellets to the fire. Or, if your stove or flue is clogged up the auger motor should stop feeding.

To review, the vacuum pressure switch allows the auger to run as long as there is sufficient negative pressure.

If you are sure the exhaust fan is running properly and the stove and flue are clean, and the auger appears not to be jammed and you are positive that all doors are sealed, (check the ash drawer door), and the auger motor fails to turn, you very well may have a problem with the vacuum pressure switch.

The first thing you want to do after you unplug the stove is examine the hose looking for a break, if its broken the break will most likely be where the hose connects to the stove as that is where the hose is exposed to the most heat. Next, disconnect the hose from the switch and see if you can blow air through it. If you can’t you will want to ream out the metal tube that the hose connects to with a stiff wire.

If none of the above corrects the problem you will want to bypass the switch temporarily to see if it needs replacing. The switch will have two wires connected to it, but some switches will have three places to connect to so take a good look before you disconnect the wires from the switch. A simple trick to bypass the switch is to use a flat type automotive fuse and connect the wires from the switch (they have female spade type connections) to their male counterparts on the fuse. Check it out, does the auger work with the vacuum pressure switch bypassed? If it does and the fire burns bright and clean with no sooting of the glass then you will need to replace the switch. I do not recommend leaving the switch bypassed! It is a safety feature designed to shut off the auger in the event of a exhaust fan failure or a flue blockage.

One Response to “The Vacuum Pressure Switch”

  • Wayne:

    Was searching for info on this since a friend was having problems with her pellet stove and I narrowed it down to this switch. Your explanation confirmed what I thought that this switch does. I have bypassed it for the night since it was her sole source of heat and her house was freezing and she has kids, but I will go back first thing in the morning and check the other things you recomended. I checked the blower and exhaust pipes and all seems to be clear and working fine so I can now feel comfortable and able to sleep tonight. I hate bypassing anything, (THEY’RE PUT THERE FOR A REASON. If all the other items mentioned check out I’ll replace the switch An excellent article, straight forward, easy to read and understand. Thanks