Hayward Heater bD Code: (Causes & Fixes)

The Hayward bD Code is a common error for the Hayward pool heaters. It indicates problems with the electrical control board (ECB). The control board oversees the operation of your heater, including monitoring temperature and safety features.

In short, the Hayward Heater bD Code means there is a problem with the control board located on the right side of the heater. This can be caused by an open FC4 Fuse, faulty wiring, or a secondary high voltage fault.

What Causes Hayward bD code?

1.      Bad Board or Secondary High Voltage Fault.

A bad electrical control board will often trigger the bD error code. However, a few issues within your Hayward heater system can result in a bad electrical control board. These are outlined in the chart below.

How to diagnose a bad electrical control board

1.        Ensure that the FC4 fuse is not open (see in the next section of this guide on troubleshooting an open FC4 Fuse).

2.       Verify the fuse board’s high voltage output by measuring for 120 VAC.

3.       Ensure that the harness is not defective. (Measure for the presence of 120VAC).

4.       Verify that the transformer is non-defective.

5.       Check if you have a defective fuse board

FIXES

This is how the above steps can help us fix the possible causes for the bD error code.

1.       When you have a bD code on your pool heater, you first want to verify that the FC4 fuse is not open on the fuse board. You can do this by removing the FC fuse from the fuse holder (assuming you have the multimeter at hand).

Then measure continuity across the fuse. If the fuse is open, Jump to the next section of this guide (Open FC4 Fuse.) Otherwise, if it’s closed, move to the next step.

2.       If there is no high voltage from the fuse board, you will likely have the bD code displayed; therefore, if there is no problem with your FC4 fuse, measure for 120VAC across pins 3 and 5 of the P6 receptacle on the Fuse board. Otherwise, if the fuse board is Ok, go to the next step.

3.       If the fuse board is Ok, check whether the harness is defective or not. Start by disconnecting the plug from the E10 connector of the control module.

Then measure for 120VAC across pins 1 and 3 of the plug-on harness. If ok, replace the control module.  If not, replace the harness. If there is no problem, reconnect the plug and move to the next step.

4.       Check whether the transformer is defective or not. At this point, you’ll need to disconnect the plug from the P4 connector of the fuse board, then measure for 120VAC between pins 4 and 6 of the plug from the transformer.

If the transformer is defective, it will need a replacement. If the transformer is Ok, you may be dealing with a defective fuse board.

5.       If the fuse is defective, replace it.

2.      Open FC4 Fuse

Another major cause for the Hayward heater bD code is an open FC4 Fuse. The following chart shows possible causes for an open FC4 Fuse and the main fixes for each.

How to diagnose an Open FC4 Fuse

1.       Check whether the igniter wiring is faulty or not.

2.       Ensure that there is no fault in the blower wiring too.

3.       Verify that the igniter is not defective

4.       Check that the blower is not defective

5.       Verify that the control module is not defective

FIXES

1.       The first thing you want to do when you are troubleshooting an open FC4 fuse is to check whether you have faulty igniter wiring or not.

For this task, you’ll need to inspect the wiring on your igniter. Ensure that the insulation on the wiring is not worn. Repair any worn-out wires if igniter wiring is Ok. Go to the next step.

2.       Is your blower wiring faulty?  If the wiring on the blower is faulty, it can cause the bD error. To rule out faulty blower wiring, inspect it and ensure that the insulation on the wiring is not worn. 

If there isn’t a problem with the blower wiring, proceed to the next step.

3.       A defective igniter will often result in a Hayward bD error, so it’s essential that you check whether your igniter is working or not.

To do that, you’ll first need to disconnect the igniter from the control module and measure the resistance across the ignitor.

Normal resistance should be within 10.9-19.7 ohms at 77°F. If the resistance you have measured is significantly out of this range, replace the igniter. Otherwise, if the igniter is good, go to the next step.

4.       If the above steps in our troubleshooting do not show any problems with the respective components, try checking for a defective blower.

Start by disconnecting the blower plug from the control module to check for a defective blower.

Then measure the resistance across the blowing windings. Normal Winding resistance across lead should be in the range of Red-to-White: 4 to 5 ohms.

If you measure anything that substantially varies from these values, your blower is mostly likely defective, and you’ll need to replace it. Otherwise, go to the next step5.

If everything above doesn’t help, you might have a defective control module. In case of a defective control module, a replacement will be required.

Other Hayward Heater Error Codes:

• LO Code
• SF Code
• AO Code
• IF Code

Tim David

HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.