Hayward HS error code


Active member
Mar 4, 2015
Yesterday my Hayward 350HDN turned off and displayed the HS error code meaning the temperature is too high. I turned off the breaker and restarted it and though I had it fixed after runner fo a few seconds I heard a rumbling sound and it shut off again showing HS. After restarting it again and having the same result I realized the rumbling sound was boiling water. My first thought was perhaps some calcium scaling broke loose and clogged the piping in the heater but the output appears as strong as normal and it gives the error code LO when the flow is insufficient such a a dirty filter. Any thoughts?


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Check your filter pressure.

Heater overheats are often caused by low water flow. Usually from a dirty filter.

Post pics of your equipment.