Has Your Outdoor Furnace Overheated?

Has Your Outdoor Furnace Overheated?

Has Your Outdoor Wood Boiler Overheated?

How To Avoid Permanent Damage?

If your outdoor wood boiler has overheated, you may have a problem that will permanently damage your boiler. This must be addressed immediately!  

We recommend that you evaluate the possible causes (listed below) and the corresponding solutions (also listed below) so that you can take the necessary steps to PROTECT your outdoor boiler from permanent damage.

  • High Limit Switch needed to be reset. Why?
  • Your Outdoor Wood Furnace overheated
  • Water temp is over 190, in some cases over 210.
  • Water/steam boiled out vent tube
  • High limit switch tripped
  • No power to light and blower fan
  • Water level dropped (boiled out)
Possible Causes: Solutions:
Door left open

An unlimited supply of air to the firebox is bad - it will lead to uncontrolled burning of wood fuel in the firebox that will damage the firebox steel.

Please never leave the furnace firebox door open for extended periods of time. The door should only be open for brief moments to add wood fuel to the firebox and remove ash. 

Pump failure Remove the silver button on the face of the pump while it is in operation to verify the impeller shaft is spinning. If not, replace the pump. See the article on how to diagnose pump failure by clicking on this link HERE. For replacement pump special, call (231) 861-8200 or check available circulating pumps here.
The high limit switch cannot be reset

Must wait until the water temp drops below approx. 150 degrees to reset. Also, High Limit Switches have only a limited number of trips in their lifespan.

This depends upon how hot and how many times the furnace has high temps. A very high temp situation may kill the switch in one trip. Or it may last 12+ trips.

Always have a spare on hand. Click HERE for more info on High Limit Switches. For replacement of high limit switch CLICK HERE.

Power outage/poor quality power ca Can cause the boiler pump to stop running. If this happens while the fire is burning hot, then without the pump circulating water, the water temp in the outdoor wood stove will rise and likely trip the high limit switch. Turn off breaker for 3 min, turn back on. Reset the high limit switch by pressing the red button until it clicks and the fan and light have power.
Poor outdoor boiler door seal rope / Fan Seal

Again, an unlimited supply of air to the firebox is bad - it will lead to uncontrolled burning of wood fuel in the firebox that will damage the firebox steel. If the door gasket is more than 2-3 years old, replace the door seal gasket. Click HERE for more info.


Also, if you installed a new fan, the seal around the two fan openings (inlet and outflow) must be tight. New furnaces are shipped with a gasket, replacement fans must have our High Temp Silicone Caulk applied to this seal to prevent air leaks.


Wood load too close to your outdoor wood burner front door Wood load too close to your outdoor wood burner front door. Wood, ash, and hot coals must not be located within 6-8 inches from the inside of the front door frame (inside wall of firebox)
Damper not closing properly

Take off the fan cover box on the front firebox door (for GX Series boilers, locate the fan in the rear of the boiler). Actuate the fan switch a few times to watch the solenoid opening and closing the damper to verify proper operation. If not closing properly, adjust as needed. If you need a new solenoid click HERE.

Aquastat Out of Calibration

Occasionally, an aquastat that is set to turn off the blower fan at 180 degrees might not turn off the blower fan until the temp reaches 185F. If this happens, a raging fire may continue burning after the blower fan is turned off at 185F for a few minutes and the 190 safety limit switch may get tripped. This is more often the case when the heat load is low on a warm fall day.

The solution is to simply lower the aquastat upper limit setting, say from 180 down to 175 or lower.

Aquastat Failure

While uncommon, aquastats can fail. If all of the above possible causes have been eliminated, replace the aquastat.


For more information contact us or visit our online store for other outdoor wood boiler parts!

Our goal at OutdoorBoiler.com is to help you realize the best return on your investment!  We have invested MILLIONS in research, testing, and proving our designs and methods. We want YOU to benefit from all we have learned!

Always remember these maintenance and operation items to keep your wood burning furnace heating system stay healthy for decades, allowing you to Stay Warm and Toasty, and Save Money on Your Heating Bills!