---
title: "Hayward Pool Heater Bo Code"
canonical: "https://gadgetguides.org/hayward-pool-heater-bo-code/"
author: "Arian"
published: "2026-09-12T22:46:34+00:00"
modified: "2026-09-12T22:46:34+00:00"
language: "en-US"
site: "Gadget Guides"
description: "Your Hayward pool heater just flashed the \"Bo\" code, and the pool is getting cold. That's frustrating. Here's the good news: the Bo code is your heater…"
categories: "Help Guide"
attribution: "Gadget Guides (https://gadgetguides.org/)"
---

# Hayward Pool Heater Bo Code

Your Hayward pool heater just flashed the "Bo" code, and the pool is getting cold. That's frustrating. Here's the good news: the Bo code is your heater telling you something specific, not a random failure.

 

It stands for "blocked outlet," and it's one of the most common and fixable issues you'll see. You don't need to be a technician to sort it out.

 

Manufacturer specifications indicate that the Bo code refers to a safety interlock that trips when the vent or exhaust path isn't clearing properly. That means either something is physically blocking the flue, or a sensor is falsely detecting a blockage. Most cases take less than thirty minutes to solve, and many fixes cost you nothing at all.

 

As of 2026, the troubleshooting logic below holds true across the entire Hayward H-series and HP-series lines.

 

![Hayward Pool Heater Bo Code](https://gadgetguides.org/wp-content/uploads/2026/09/hayward-pool-heater-bo-code-mtyz5e0u.webp)

 

Image source: Bing (Web (fair-use with source credit))

 

## The Bo Code Explained (What Your Heater Is Actually Telling You)

 

The "Bo" or "bO" code means "blocked outlet." The heater is saying, "I tried to exhaust my gases and couldn't."

 

Here's how it works. When your heater fires, combustion gases rise through the heat exchanger and out the top vent. A pressure switch sits in the exhaust path and monitors airflow.

 

If the vent is clogged, smoke can't get out, and the pressure switch never closes properly. The control board reads that as a problem and shuts the heater down before gases back up into the pool area.

 

That safety shutdown prevents carbon monoxide from filling your backyard and keeps the heater from overheating. The code can appear instantly on startup or after the heater runs for a few minutes. If it appears right away, you're likely dealing with a sensor or electrical issue.

 

If it appears after the heater has been running, you're likely looking at a real vent blockage or a high-wind condition.

 

Either way, the fix follows the same diagnostic path. The Bo code is not a death sentence for your heater. Aggregate repair data shows it's one of the most common, least expensive, and most beginner-friendly issues to resolve.

 

It's usually a cleaning problem, not a component failure.

 

One more thing worth knowing: the Bo code is different from an "F" code (flame failure) or an "HLS" code (overheating). Those point to other issues. Bo specifically means airflow.

 

Don't waste time testing the gas valve first. Start with the vent.

 

## Quick Answer: The 3 Most Common Fixes (Try These First)

 

The Bo code means a blocked vent stack or a faulty pressure switch. Exhaust gases can't escape properly. Clear any debris from the vent first.

 

Then test the pressure switch. Replace it if the code returns.

 

These three fixes handle the vast majority of Bo code calls. Try them in this order.

 

| Fix | What It Does | Time to Try |
| --- | --- | --- |
| Clear the vent stack | Removes leaves, soot, or nests blocking exhaust flow | 10 minutes |
| Clean the pressure switch hose | Restores the vacuum signal to the sensor | 5 minutes |
| Replace the pressure switch | Fixes a worn-out sensor that falsely trips | 20 minutes |

 

Start with the cheap, easy stuff. If the vent is clear and the hose is clean, the switch is your next suspect. Most pool owners handle all three in less than half an hour.

 

You'll need a screwdriver and maybe a small wire brush. A multimeter helps, but it's not required.

 

**To clear the vent:** lift the flue cover, peer inside with a flashlight, and vacuum out anything that doesn't belong. Spider webs, wasp nests, and dead leaves are the usual suspects. Soot means a combustion problem deeper in the unit.

 

**To clean the pressure switch hose:** locate the rubber tube attached to the pressure switch. Slide it off, inspect both ends, and blow through it. If it's blocked, replace it.

 

A short length of 1/4-inch silicone tubing is the standard repair part.

 

**To replace the pressure switch:** unscrew the old switch, disconnect the wires, and install the new one. Match the wiring diagram on the inside of the panel. Reset the heater and watch the code.

 

If the code disappears after clearing the vent, you're done. But watch for repeat trips. A heater that clogs repeatedly probably has soot building up from a rich fuel mixture.

 

That's a separate issue. If the code stays, move to the pressure switch hose. Cracks are easy to miss, so bend the hose while you inspect it.

 

The switch itself can fail. It's a safety part, so don't skip testing it.

 

Before you start, turn off the power and gas to the heater. Wait for the unit to cool if it's been running.

 

## Step-by-Step Diagnostic Flow: From Symptom to Solution

 

Follow these steps in order. Each one rules out a cause or confirms it.

 

### Step 1: Rule Out the Obvious (The 30-Second Visual Check)

 

Start here. Walk around the heater and look up. Is the vent stack clear?

 

Check the top of the flue for leaves, pine needles, or a wasp nest. Then kneel down and look under the heater. Any debris around the burner compartment can cause airflow issues.

 

### Step 2: The Pressure Switch Test (The Most Likely Culprit)

 

![Hayward pool heater pressure switch](https://gadgetguides.org/wp-content/uploads/2026/09/hayward-pool-heater-pressure-switch-mtyz5f2c.webp)

 

Image source: Bing (Web (fair-use with source credit))

 

The pressure switch is a small round sensor near the top of the firebox. It has a rubber hose connecting it to the exhaust path. That hose is the weak link.

 

Remove it, check for cracks, and blow through it to confirm it's open. Then test the switch itself with a multimeter. On most Hayward models, the switch should show continuity (closed circuit) when you blow gently through the nozzle.

 

If it stays open, the switch is stuck and needs replacing. A pressure switch costs between $20 and $40, and it snaps in place in about ten minutes.

 

### Step 3: Dig Deeper – Vent Blockage, Soot, and Nesting Pests

 

![blocked pool heater vent stack](https://gadgetguides.org/wp-content/uploads/2026/09/blocked-pool-heater-vent-stack-mtyz5h07.webp)

 

Image source: Bing (Web (fair-use with source credit))

 

If the pressure switch and hose check out, the blockage is somewhere else. Remove the top vent cover and look inside with a flashlight. You might see soot hardened into a crust.

 

Soak it with water and scrape it off. Or you might find a wasp nest that was built in the spring. Both are common.

 

Use a shop vacuum to pull out any loose material. After cleaning, reset the heater and try a cycle.

 

### Step 4: The Control Board and Electrical Side (Less Common but Real)

 

If you've cleared the vent, inspected the hose, and tested the switch, the problem might be electrical. Check the control board for burnt spots, swollen capacitors, or a loose wire connector. Also check the rollout switch, which is a small button on top of the firebox.

 

It can trip on its own after a temperature spike. If the button is popped out, press it to reset. If the heater still throws the Bo code, the control board itself is likely the issue.

 

That's a job for a technician.

 

If any step fixes the code, you're done.

 

## Mistakes That Cost You Time and Money (Don't Do These)

 

Here are the ones to avoid.

 

- **Bypassing the pressure switch.** This is the most dangerous mistake. Jumping the switch forces the heater to run without a vent safety check, which can push carbon monoxide into the air. Never do this, even temporarily.
- **Resetting the heater over and over.** If you press the reset button and the Bo code comes back, you haven't fixed the problem. You're just burning gas. Fix the airflow issue first.
- **Cleaning a hot heater.** The firebox stays hot for a long time after shutdown. Touching the vent top or pressure switch while hot can cause burns. Wait at least 30 minutes.
- **Replacing parts randomly.** Some owners buy a pressure switch, a thermistor, and a control board before finding out a leaf was covering the vent. Test first, buy parts second.
- **Ignoring soot.** Soot inside the firebox or heat exchanger says the gas-to-air ratio is off. That's not a vent issue. That's a burner or gas valve problem that needs a pro.
- **Using the wrong hose.** Replacing the pressure switch hose with a random rubber tube can cause false readings. Use the proper silicone tubing or a genuine Hayward part.

 

All of these mistakes share one theme: they treat the symptom instead of the cause. The Bo code is a diagnostic tool, not the enemy. Let it guide you.

 

Take the guy who resets his heater every morning during swim season. He spent two weeks blaming the wind. Then he found a nest in the flue.

 

Ten minutes with a screwdriver fixed it. The opposite also happens: a tech call that cost $150 just to clean the vent. That's the bill you avoid by trying these steps first.

 

Cheap checks before expensive parts.

 

## When to Call a Pro (And When You're Safe to DIY)

 

You can handle this yourself if you've cleared the vent, tested the pressure switch, and checked the hose. Those three checks solve most cases. If the code still says Bo after all of that, stop guessing.

 

Call a pro if:

 

- **You smell gas at any point.** Shut off the gas supply, leave the area, and call your gas utility or a licensed technician immediately.
- **The heater fires but keeps shutting down.** That points to a gas pressure or combustion issue, not a simple blockage.
- **You see soot spilling into the heater cabinet.** That's a burner problem, and adjusting it wrong can create carbon monoxide.
- **You're not comfortable working around gas or electricity.** No shame in that. A service call is cheaper than an ER visit.

 

The U.S. Consumer Product Safety Commission has reported on carbon monoxide hazards from pool heaters for years, so treat any gas-related oddity seriously. If you're ever in doubt, shut the heater down and call a qualified service company.

 

A qualified tech will measure gas pressure, check the orifice size, and verify the heater is running within the parameters set by the ANSI Z21.56 standard. That's beyond any DIY toolkit.

 

When you call for service, tell them the code and what you've already tried. That saves time and money. A good tech will confirm your work and move on to the deeper checks.

 

If the heater is more than 10 years old, they might also flag worn components like the gas valve or thermistor.

 

Your safety matters more than the repair cost.

 

## Frequently Asked Questions

 

### What does the Bo code mean on a Hayward pool heater?

 

It means "blocked outlet." The heater detected that exhaust gases are not venting properly. It shuts down as a safety measure to prevent carbon monoxide buildup.

 

### Can I reset the Bo code and keep using the heater?

 

No. Resetting without fixing the underlying problem is dangerous. The code will return until you clear the vent blockage, repair the pressure switch hose, or replace a faulty pressure switch.

 

### Why does my heater show Bo even after I cleaned the vent?

 

Check the pressure switch hose for cracks or blockages. Then test the pressure switch itself with a multimeter. If both are fine, the control board may be failing.

 

### How much does it cost to fix a Hayward pool heater Bo code?

 

DIY fixes cost nothing to about $40 for a replacement pressure switch or hose. A service call runs $150 to $300 depending on your area and the issue depth.

 

### Is it safe to bypass the pressure switch to test the heater?

 

No. Bypassing the pressure switch disables a critical safety interlock and can cause carbon monoxide to leak into the pool area. Never do this.

 

### What causes the Bo code to appear only in windy weather?

 

Strong wind can create backpressure that tricks the pressure switch into thinking the vent is blocked. Adding a wind shield or extending the vent height may solve it.