Where are fan limit switches located?
Most fan limit switches are located near or at the convection fan housing to switch the room blower ON once the stove is warm enough.
A Low Limit Sensor is usually mounted to the exhaust fan housing, it will close after sensing heat allows the stove to run.
Can I BYPASS a fan limit switch?
YES you may do this to test the function of a fan switch to find a fault on your pellet stove. Don't use a paper-clip, this may cause a short circuit and possibly damage a expensive control board!
I always plug the two wires to a flat 5A car fuse for a quick test. I do not recommend to leave a bypass on over a long time and without any supervision, better safe than sorry!
Can I RESET a fan limit switch?
Fan limit switches are just plain ON/OFF switches to control a fan, they never have a reset button installed. If your switch has a reset button, this it is clearly a HIGH LIMIT SWITCH!
Other names for a pellet stove fan limit switch:
Pellet stove manufacturers use different terms for the same control switch, here are a few names:
fan limit switch, blower control, snap disc limit switch, proof of fire POF switch, fan limit control, exhaust heat sensor, low limit switch, low limit exhaust temperature sensor
How an pellet stove fan control switch works:
The contacts on a fan blower switch are normally open, they close on temperature rise.
Modern pellet stoves use fan limit switches in three totally different operations:
· Using a fan limit switch to turn the room blower (convection fan) ON or OFF:
The convection blower draws room air into the stove and pushes the cold air around a series of heat-exchange tubes. The temperature inside the heat exchanger is about 250ºF, hot enough to warm up the ambient air-stream.
After ignition, it takes a while for a pellet stove to warm up, you don’t want the fan pushes cold air into the room at this time.
Once the system warms up, the fan switch closes and powers the fan ON.
When the heating cycle stops, there is still a lot of heat available in the heat exchanger. The fan switch keeps the fan running until the warm air is cooling down below the operating temperature of the control switch.
· Using a proof of fire switch to verify that the pellet stove successfully ignited;
Failure to start: Many modern pellet stoves control the start-up sequence to ensure a successful ignition. At the beginning, the auger motor feeds a minimal amount of pellets into the burn-pot to start a new ignition procedure. If the fan low limit switch does not confirm a minimum operating temperature within the startup period, the stove will shut down and display an error.
· Using a convection fan control switch to set the fan speed automatically on high;
Most pellet stoves incorporate a control device to let you select a room blower fan speed.
The convection fan control switch automatically sets the fan on high when your stove is generates heat faster than the fan is able to distribute it into the room. This happen when the fan sped is set to very low. Once the fan is turned ON to high speed for a while, he may continue to cycle between high-speed and the pre-selected setting.
If your pellet stove shuts off after 15 minutes even though pellets are still burning, you likely need to replace the proof of fire switch (POF), also called the low-limit disc switch.
f your pellet stove shuts off after 15 minutes even though pellets are still burning, you likely need to replace the proof of fire switch (POF), also called the low-limit disc switch. Most pellet stoves have this switch installed on the blower housing with a rating that is typically around 110ºF to 140ºF.
TROUBLESHOOTING TIP: Check the damper settings; please read the included tips and instructions for pellet stove troubleshooting!
