2 year old Hayward Mdl #H400FDP, will only heat for around 5 minutes (raising the spa aprox 2-3 degrees F) before the high limit on top of the manifold outlet opens. (Labeled for 135 degrees F) Then high limit then closes and with the auto reset heater kicks back in again in 2 minutes. This cycle continues until it reaches the desired temp setting. Is it typical for a high limit to lose its accuracy or it it more likely a system problem? Filter and basket clean. Water flow seems good. Is there a mixer valve in the water manifold that can cause the water temp to exit to high? Any other suggestions? Thx

there are several causes of a bD code on hayward heaters. because of this, i have included the link to the code page so you can eliminate and review them.
https://hayward-pool-assets.com/assets/documents/poolscanada/pdf/manuals/universal-h-series-owners-manual.pdf?fromCDN=true

need more ifo on error code check on hayward web site

Thank you for posting your question here on Fixya.com.

A 'LO' error code for a Hayward heater is a limit string open error. If the limit string opens the heater shuts down and goes into lockout. Automatic restart is 2 minutes after the error condition is corrected and the limit string closes.

The limit string is a series of switches designed to turn off the heater if air or water temperatures exceed a safe operating limit.

The problem may be faulty a switch(es) but is far more likely to be a system condition the switches are reacting too that needs to be corrected. Low flow of combustion air due to obstructions around the heater or the vent; low flow of water through the heater allowing too high a water temp; Poor venting or sooted-over heat exchanger causing flame rollout. These are all conditions that should be eliminated if they exist.

If you are not familiar with these switches or the conditions described you may want to consider calling in a professional. Hayward can refer you to someone in your area who is. Call Hayward at 908-351-5400 or try the website locator found here.

If this answer does not fix your problem, please comment with additional details prior to rating the answer. You may also contact me thru our website at www.arrowpools.net. Positive feedback is appreciated once your problem is solved!

John

The part number is FDXLWPS1930 and should cost you $20-$25 if bought locally although it could be up as high as $40.

John

the pump is not circulating, so the high limit is shutting it off. You need to check out your circulating pump

smeel gas? clean burners

would not suggest trying to manually light,its an electronic ign model so you may damage some wires with an open flame.try powering off then turning back on and see if display retuns to normal

check millivolt output,if it is in normal range(400-600)check for continuity on pressure switch,flame rollout and high limits.