Hayward H-250 gas heater not reaching desire temperature


New member
Jul 27, 2011
Hello everyone. Posted last year and appreciated your suggestions, so i've come back for some more insight. Similar to the person who posted here http://www.troublefreepool.com/gree...l-more-slowly-t44766.html?hilit=hayward h 250, my Hayward H-250 gas pool heater is not coming to the desired temp this year. It is lit, the pressure switch is as high as it can go (too high and the heater won't light), and water pressure is fine. In fact, water pressure is actually better than last year actually as I replaced the sand in the sand filter and did some maintenance.

It is pumping water out at 85 F, but last year my wife left the heater on overnight and we woke up to a pool that was 94 F so I know when its set to max it is supposed to be higher. By contrast, its been on the better part of all weekend and the pool temp is at 81 and this seems pretty much like the max its going to get.

Please keep feedback basic as I'm still new to pool stuff. Cost me $140 for a tech to come in and stand there and look at it last year, so would prefer to at least do the basics myself. Thanks in advance, and hopefully can help others as well somewhere along the way.


TFP Expert
Apr 15, 2007
Ft Lauderdale, Florida
Did you run it overnight?
You can also check the temperature difference between the incoming temp and outgoing temp by using your thermometer in the skimmer, and at the closest return jet. A normally running gas heater should give you 7 - 10 degrees F increase.
Less than that, and you probably have too much flow through the heater, or your internal bypass valve is stuck opened.
More than that, and you probably have low flow, but should be getting your temperatures up to your desired setting.

The protection devices within the heater will not typically cause it to not reach temps, unless the thermostat is damaged. They are usually ON or OFF switches, so they are either working or not.


Well-known member
May 26, 2011
Im not sure if this will be any help but last year I noticed my Hayward H250 doing the same thing... Used to heat up the water very quickly and was no longer doing it. This year when I started the pool the heat exchanger sprung a huge leak. I am waiting on a new heat exchanger to come. Fed Ex should be delivering it tomorrow so I can replace it. My heater is 7 years old.