Burnham boiler B codes mean the control board detected a fault and stopped the boiler. These are soft lockouts. Most B codes clear when you cycle power off then back on. But when the fault returns immediately, the root cause is still in place. That is the difference between a B code and a hard lockout. Hard lockout codes like some E codes need a manual reset. B codes do not.
If your Burnham boiler shows B08, B09, or B26, work through the steps below. Do not chase symptoms. Find the real cause. Then fix it.
B08 - Pressure Switch Open
B08 is the most common Burnham fault code. The pressure switch stayed open while the inducer fan was running. The control board sees the inducer running but does not see the switch close. It flags the fault and stops the boiler.
The top cause is a blocked condensate drain line. Burnham boilers use a condensate trap with an internal float. When the trap fills with water, sludge, or debris, it blocks the pressure switch port. The inducer runs fine but the pressure switch never closes.
Step 1: Clean the condensate trap.
Remove the trap from the boiler. Flush it with warm water. Clean the internal float mechanism. Make sure the float moves freely. Check the small pressure port on the trap for any obstruction. A toothpick or small wire works for clearing the port hole.
Step 2: Check the drain hose.
Look for kinks in the drain line. Straighten any bends. Remove any blockages. The drain must flow freely by gravity. If the hose runs uphill at any point, condensate backs up into the trap. That alone can trigger B08.
Step 3: Test the pressure switch.
Use a manometer to test the switch. Most Burnham pressure switches close between -0.5 and -1.2 inches WC. Connect the manometer to the switch port. Run the boiler. If the switch does not close within that range, replace it.
Step 4: Inspect the inducer motor.
A failing inducer may not generate enough draft. Check the inducer wheel for debris or damage. Listen for unusual bearing noise. If the inducer motor is weak, it pulls less vacuum. The pressure switch never closes. Replace the inducer if it is failing.
B09 - Limit Circuit Fault
B09 means the control board detected an open limit in the safety circuit. This can come from a high-limit aquastat, an auto-reset limit, or a low water cutoff. The safety chain is broken somewhere.
Step 1: Check system pressure and water level.
Low water triggers limit circuits. Look at the pressure gauge on the boiler. Residential systems should run around 12 to 15 PSI cold. If pressure is low, add water through the feed valve. Check for leaks in the system. A slow leak over days or weeks can drop the water level below the safety cutoff.
Step 2: Purge air from the system.
Air in the pipes prevents water circulation. Air-bound zones trap water in one spot. The boiler overheats locally. The limit trips. Bleed each zone starting from the lowest point in the system. Work your way up. Keep bleeding until a steady stream of water comes out with no air sputtering.
Step 3: Verify the circulator pump.
A stuck circulator pump stops all water flow. The boiler fires, the water inside goes from cold to overheated in minutes, and the high-limit trips. Feel the pipes near the pump. Cold on both sides means no flow. Check the pump coupling. If the pump hums but the shaft does not turn, the coupling may be broken. Replace it. Make sure the pump has power and the speed setting is correct.
Step 4: Test the high-limit aquastat.
The high-limit aquastat should be closed. Use a multimeter to test continuity across the limit terminals. If it is open, test whether it opens at the correct temperature. Most Burnham aquastats are set between 180 and 200 degrees. If it opens too early or fails closed, replace it.
B26 - Safety Limit Open (Manual Reset)
B26 is more serious than B09. A manual-reset limit device tripped. This could be a rollout switch, a blocked vent switch, or a manual-reset high limit. You can clear B26. But you must fix the cause first.
Step 1: Find the tripped device.
Look on the burner panel for a small red button. That is the rollout switch. Some Burnham boilers have a blocked vent switch on the vent pipe. Others mount a manual-reset high limit on the boiler front. Which device tripped tells you what went wrong.
Step 2: Diagnose why it tripped before resetting.
Do not reset and walk away. If the rollout switch tripped, look for soot around the burner. Soot means incomplete combustion. Cracked heat exchangers produce soot and rollout. If the blocked vent switch tripped, check for condensate backup in the vent. Water in the vent restricts airflow. The boiler overheats. The safety device opens.
Step 3: Press the red reset button.
Press the reset button firmly until it clicks. You should feel a positive snap. If the button feels loose or does not click, the device may be damaged. Replace it.
Step 4: Cycle boiler power.
Turn the boiler off at the disconnect. Wait 30 seconds. Turn it back on. This clears the fault from the control board. If B26 returns right away, the underlying problem is still present.
Complete Error Code Table
| Code | Meaning | Common Fixes | | B08 | Pressure switch open with inducer running | Clean condensate trap, clear drain hose, test pressure switch, check inducer motor | | B09 | Limit circuit open | Restore water level, purge air from zones, verify circulator pump, test aquastat | | B26 | Manual-reset safety limit tripped | Find the tripped device, diagnose the root cause, press red reset, cycle board power |
When to Call a Professional
B26 involves safety devices that protect against fire and carbon monoxide. If a rollout switch trips repeatedly, do not reset it without finding out why. A cracked heat exchanger can produce Carbon Monoxide. That is a life safety hazard.
B08 that returns after cleaning the condensate line may point to a failed pressure switch. Replace it. B09 that returns after confirming circulation may be a bad high-limit control. Replace it.
In all three cases, if you run through the steps above and the fault keeps coming back, do not keep resetting the boiler. Call a licensed boiler technician. Some faults need a combustion analysis. Some need a heat exchanger inspection. Some need a control board replacement. A good technician gets to the root cause quickly.