DIY Error Codes

Hayward Universal H-Series gas pool heater Error HS

Water temperature sensing error. It clears when inlet water is 104 °F or less, or temperatures stabilize.

Note the code. It clears when inlet water is 104 °F or less, or temperatures stabilize. If HS comes back, call a qualified pool heater technician.

Start the fix →When to call a pro ↓
Full answer & models

Hayward HS on a Universal H-Series heater means water temperature sensing error. If it keeps returning, Hayward says to contact a qualified service company.

Applies to: H150FDH200FDH250FDH300FDH350FDH400FDH500FD
Also searched as: Hayward heater H5, Hayward heater error HS, Hayward H-Series HS code, Hayward pool heater H5 code

Gas appliance. Service only by a qualified technician; power off before any service.
Why
Hayward, what to do if you smell gas: do not try to light any appliance; do not touch any electrical switch and do not use any phone in your building; immediately call your gas supplier from a neighbor's phone and follow their instructions; if you cannot reach your gas supplier, call the fire department. Installation and service must be performed by a qualified installer, service agency, or the gas supplier. Hayward: before installing or servicing this electrical equipment, turn the power supply off. Hazardous voltage can shock, burn, cause death or serious property damage.

What HS means

Water temperature sensing error. It clears when inlet water is 104 °F or less, or temperatures stabilize.

More detail
Hayward's Universal H-Series owner's manual (Figure 4, Error Codes) lists HS as "Water temperature sensing error": Either the inlet water temperature sensor reads above 104 °F (normal operation resumes 2 minutes after it reads 104 °F or less), or the inlet temperature is rising faster than 6 °F in 60 seconds, indicating a potentially damaging low water flow condition. If this is detected 3 times in one hour, the heater locks out until electrical power is cycled off and on. The manual's instruction for error codes is to contact a qualified service company for assistance.

5-minute checks

Fix it step by step

Step 1 of 3

  1. Note the code and wait

    • 2 min
    • None
    • DIY

    Safety: Gas appliance. Service only by a qualified technician; power off before any service.

    Normal operation resumes 2 minutes after the inlet sensor reads 104 °F or less, or when temperatures stabilize.

    More detail

    Note the code and wait.

    Write down the code and when it appears. Per Hayward's Figure 4: Normal operation resumes 2 minutes after the inlet sensor reads 104 °F or less, or when temperatures stabilize.

    Did the code clear?

  2. Check that the pump is running

    • 2 min
    • None
    • DIY

    Low water flow is one cause Hayward lists.

    More detail

    Check that the pump is running.

    Hayward's description of HS includes a rapid temperature rise "indicating a potentially damaging low water flow condition", and the manual says the heat exchanger must be protected from insufficient water flow. Confirm the filter pump is on.

    Did the code clear?

  3. Call a qualified service company

    • Decision
    • None
    • Pro decision

    Stop here and book a qualified technician.

    More detail

    Call a qualified service company.

    Hayward's owner's manual says to contact a qualified service company for assistance with error codes. Installation and service must be done by a qualified installer, service agency, or the gas supplier. Do not open the heater cabinet yourself.

    Still showing HS?Need a pro → call a pro

Code cleared. Nice work.

Watch the display for a day to make sure it stays clear.

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Fixed after any step? Watch the display for a day to make sure it stays clear. Still HS after step 3? call a pro.

Call a pro if…

  • You smell gas (leave first, then call your gas supplier from a neighbor's phone).
  • HS keeps coming back or the heater stays in lockout.
  • Anything that needs the heater cabinet opened or wiring checked.

FAQ

What does Hayward heater code HS mean?

"Water temperature sensing error", per Figure 4 of the Universal H-Series owner's manual. Either the inlet water temperature sensor reads above 104 °F (normal operation resumes 2 minutes after it reads 104 °F or less), or the inlet temperature is rising faster than 6 °F in 60 seconds, indicating a potentially damaging low water flow condition. If this is detected 3 times in one hour, the heater locks out until electrical power is cycled off and on.

What does Hayward say to do about HS?

Contact a qualified service company for assistance, per the manual's error-code section.

How do I clear an HS lockout?

Per Hayward, if HS is detected 3 times in one hour, the heater locks out until electrical power is cycled off and back on. If it keeps happening, call a qualified service company.

Source: Hayward Universal H-Series Owner's Manual (H150FD-H500FD), Figure 4 Error Codes, pp. 13-14; safety, pp. 1 and 3. Written by the DIY Error Codes team. Updated 2026-10-16. DIY Error Codes is independent and not affiliated with or endorsed by Hayward.