Hayward Heater HS & IO Code: (Causes & Fixes)

The HS code on your Hayward heater is a temperature-sensing error. The code helps you to be aware of any unusual temperature changes in your spa or pool water.

The Hayward Heater HS code indicates that either your water temperature has exceeded a maximum of 104°F or the water temperature is changing at an unusual rate (faster than 6°F in 60 seconds or less while the heater) is on and firing.

The error can especially occur if the pool is too small for your heater of there is little water in your pool or spa. This error can also occur due to a defective inlet water temperature sensor.

Below is a quick chart for HS code’s possible causes and the main fixes.

Instead of worrying when you see a code on your heater, you should be glad that your heater’s safety measures are working correctly. Error codes are safety measures put in place to protect your equipment from damage and for your overall safety.

So here are a few steps to diagnose the HS code on your Hayward Heater.

Steps to diagnose the Hayward Heater HS Code

1.       Check the remote thermostat settings. (Setpoint should be within limit)

2.       Verify that the water flow to your heater is adequate.

3.       Check the inlet water temperature sensor. A defective one will simply trigger this error.

For each of the possible diagnostic steps above, there are possible fixes for each of them. Let’s look at the possible fixes for each of the above.

Fixes for the HS Code

1.       Verify that the set point on the remote thermostat is 104°F or less. 

The heater usually displays the error if the temperature goes below that point. A thermostat that’s set above the limit is a common cause of issues with your pool heater.

Try to Adjust and set the thermostat to the correct temperature range if necessary.

 If you have verified that your thermostat setpoint is Ok, proceed to the next step.

2.       Because low water flow to the heater will often trigger the HS code, you’ll need to verify that your heater has adequate water flow above the minimum required (20 GPM for H150FD and H200FD, 25 GPM for H250FD, and H300FD, 30 GPM for H350FD and H400FD).

Usually, it’s the intermittent low water flow of the water that will cause the HS error code.  Otherwise, if the water flow is normal, you should go to the next step of troubleshooting this problem.

3.       Verify whether the inlet water temperature sensor is defective or not. A defective one can trigger this error code.

What you need to do at this stage is get an accurate thermostat and compare the water temperature readings. That is the reading by your heater and by the other thermometer.

If the readings vary significantly, replacing your sensor is just a good idea.

If you think you can’t troubleshoot your heater’s problems on your own, it’s always best to involve professionals.  Attempting to fix your heater without any familiarity can result in more problems that cost you even more.

That said, a few other error codes are common on the Hayward pool heaters. One of the commonest is the IO code (Igniter open error), not to be confused with IF code o (Ignition failure code) or the AO code (Blower vac switch open).

What is Hayward Heater IO code?

An Igniter open error code is triggered when the control board detects no current passing through the igniter circuit (when the circuit opens), but the blower continues to run.

The board will, under normal circumstance, turn off the blower and goes into lockout.

Below is a quick chart on the possible causes of the IO and the main fixes to that error.

Steps to diagnose and fix the IO code

1.       Check and verify that the wiring on the ignitor is intact. Inspect the igniter wiring and ensure that the igniter plug is undoubtedly attached to the control board.

2.       If the first step proves that there is no wiring problem, then check whether the ignitor itself is defective or not. A defective igniter can not complete the circuit. You can test it for continuity to rule out a defective igniter. If it’s defective, replace it.

Final Thought

A Hayward heater HS code is not an uncommon error among consumers. When it appears, you need to be aware that it’s a water temperature sensor-related issue.

We hope you have found a solution to this problem by reading through our troubleshooting guide. If not, involve professionals. Professionals have the necessary tool to troubleshoot and fix your heater problems quickly.

Thanks for reading.

Tim David

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