Hayward H300 (Natural Gas) Heater stops heating spa at 96°

frustrated

Member
Jul 25, 2014
9
Wyckoff, NJ
Standard configuration on an in-ground pool with attached spa. The heater is about 19 years old, so owes me nothing. Still heats pool without issues, however when it is heating in spa mode it consistently cuts out every time at approximately 95 or 96 degrees. Then the heater will not re-fire for some period of time. Given the consistency of the temperature at which it cuts out, is this due to some type of faulty switch or coupling which is overheating and can be replaced/repaired? Or is there something else going on? Of course, I can replace the heater but would love to try to avoid spending ~$4000 this summer if I can get another season out of it. Thanks!
 

swamprat69

Well-known member
Mar 30, 2019
271
Las Vegas, NV
If it heats the pool fine but not the spa, you might check to see if one of the temperature limits is opening to cut off the heater. If one is it might be related to a flow volume problem in the spa configuration.
 

frustrated

Member
Jul 25, 2014
9
Wyckoff, NJ
Thanks so much for your reply swamprat69. I believe that the flow volume is not the issue as the spa goes from approximately 82 degrees up to 95/96 degrees without an issue and then suddenly cuts out. I don't think that anything is suddenly impeding the flow volume when it gets to that higher temp.

Also, a very naive question, but I assume that the "temperature limit" is a physical part in the heater, not a setting? If it is a physical part, is that the technical name for it, because I am looking at the parts list for the heater and I don't see it. Does it go by another name? Thanks again.
 

JamesW

TFP Expert
Mar 2, 2011
19,703
What exact model number is the heater?

Some models have a maximum temperature lock out setting.

Check your manual for the lock out setting procedure.

Are there any error codes at all?

Is the displayed water temperature correct and less than the set temperature when it cuts out?
 

frustrated

Member
Jul 25, 2014
9
Wyckoff, NJ
Thanks for your reply JamesW. The heater is very old (~ 19 years) so it doesn't have a digital panel. Just two temperature knobs (one for pool, one for spa) that are both set to maximum. The model is an H300. And yes, the displayed water temperature, on the indoor Jandy control not the heater (due to the heater's lack of a digital display), is the correct water temperature in the spa when measured with a thermometer in the water itself. Always at 96 degrees, even though the spa temperature is set to 102. I hope this info helps. Thanks.
 

JamesW

TFP Expert
Mar 2, 2011
19,703
It might just be a bad temperature sensor.

You would have to check the thermostat to see if it is opening at the shut off temperature.