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ErrBase

Hayward Pool Heater BO Error Code: Blower Overheat

Quick Answer

Hayward BO is a blower or combustion overheat fault. Blocked air intake and exhaust vents account for 45% of BO faults because insufficient fresh air raises combustion temperatures beyond safe limits. Blower motor bearing failure is the next most common cause - a bearing-failing motor runs slower, generates less airflow, and overheats.

Hayward BO is a blower or combustion overheat fault. Blocked air intake and exhaust vents account for 45% of BO faults because insufficient fresh air raises combustion temperatures beyond safe limits. Blower motor bearing failure is the next most common cause - a bearing-failing motor runs slower, generates less airflow, and overheats. Clear venting and verify adequate clearance around the unit before inspecting the motor or thermal limit switch.

HaywardPoolheaterSeverity: highDifficulty: intermediate73% DIY Success
Time to Fix
30–120 min
Difficulty
intermediate
Parts Cost
$15 – $220
Tools Needed
Multimeter, Flashlight
Wrong code?

Not seeing BO on your display?

Select what your appliance is actually doing and we'll take you to the right guide.

combustion air blower fault
PentairERR AFS

What Does the BO Code Mean?

BO is a blower overheat lockout - most often caused by a blocked air intake or vent, or a blower motor with failing bearings.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Blocked air intake louvers reducing combustion air volume40%
Blocked exhaust vent trapping heat in combustion chamber24%
Blower motor bearing failure reducing fan speed14%
BO thermal limit switch failure (stuck closed or faulty)12%
Insufficient clearance around heater cabinet10%

Symptoms You May Notice

  • BO displayed on panel
  • Heater runs for a period then shuts down with BO
  • Blower makes grinding or high-pitched noise
  • Heater cabinet exterior unusually hot to the touch

Can you reset a Hayward poolheater to clear the BO code?

After correcting the blockage or replacing the blower or thermal limit switch, allow the heater to cool completely, then press Mode to standby, wait 30 seconds, and restart. If BO returns within the first heat cycle, an active overheating condition still exists.

Tools Required for Diagnosis

MultimeterFlashlightScrewdriver setSoft brush or vacuum

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

1

Allow the heater to cool for at least 30 minutes after the BO

Allow the heater to cool for at least 30 minutes after the BO lockout before inspecting. While waiting, visually check the clearance on all sides of the heater cabinet - Hayward requires a minimum of 12 inches on sides and 24 inches at the front.

2

Inspect the air intake louvers on the sides of the heater cabinet

3

Inspect the exhaust vent termination

4

Start the heater and listen closely to the blower motor during

5

With the heater cooled and power off

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name
Combustion blower motorCHXBLW001 · $100–$220
BO thermal limit switchCHXTLS003 · $15–$35

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs
Labor Approach
Our Verdict
REPAIR
Estimated Cost: $118 (Parts) vs $3000 (New Machine)

Frequently Asked Questions

What does BO mean on a Hayward pool heater?
BO stands for Blower Overheat. The combustion blower motor temperature or combustion chamber temperature exceeded the safe operating limit, triggering the thermal safety lockout.
Why does my Hayward heater show BO on hot days?
On hot days, ambient temperature is already elevated, which reduces the cooling effect on the blower motor. If the air intake is even slightly restricted or the motor's bearings are worn, the additional thermal load from hot ambient air can tip the balance into a BO fault.
Can I restart my Hayward heater after a BO code?
Yes, after it has cooled for at least 30 minutes. Do not force a restart on a hot heater - the thermal limit switch needs to reset to its closed position before the heater will operate normally. If BO returns immediately on restart, an active overheating condition is still present.
How far from a wall does a Hayward H-Series heater need to be?
Hayward requires a minimum of 12 inches clearance on the sides and rear, and 24 inches at the front (service clearance). The heater must not be installed in an enclosed space without adequate natural ventilation. Inadequate clearance is a common, overlooked cause of BO faults.
How do I know if my Hayward blower motor needs replacement?
Signs of a failing blower motor include: grinding or rattling noise during operation, the motor being slow to reach full speed, the exterior of the motor housing being abnormally hot, and the motor shaft showing play when wiggled by hand (with power off). Any of these indicate imminent motor failure.

Related Hayward Poolheater Error Codes

Code: HUBHayward Pool Heater Error Codes GuideCode: AOHayward Pool Heater AO Error CodeCode: RESETHow to Reset a Hayward Pool Heater

Same Fix on Other Brands

Pentair poolheaterERR AFS: Pentair Pool Heater ERR AFS Error

Models Known to Experience BO Errors

This repair applies to most Hayward poolheaters with this error code. Common model numbers include:

H400FDN, H250FDN, H150FDN, H400FDP

Last verified for technical accuracy on March 14, 2026