Pool heater acting oddly...


May 15, 2008
In case you haven't read my green pool thread, a little background info. I bought my first house in November of last year, and it came with an inground pool. I had not been looking for one, but I loved the house and thought it would be a nice little bonus. Fast forward to now, and I opened the pool for the first time and got everything up and running. Pool is finally starting to look great after being a swamp, thanks to all the fantastic advice from here.

I decided to test out the heater, and noticed some weird behavior.

First the specs, it is a Hayward H-250, probably about 7-8 years old. I believe it has the millivolt ignition, as it is plumbed in to my breaker box and I never lit a pilot light. My filter is a Pentair Clean and Clear plus 4 cartridge monster, which is a pain in the but to clean, but thats beside the point. I unfortunately don't know any other details about the repair history of the unit, as the previous owners did not leave any documentation. I did find a partially melted electronic igniter unit in the pile of random pool stuff they left, so I am assuming they had replaced it with a new unit, but I have no way of knowing if it even came from this heater. It is plumbed into the natural gas line, and has a switch for pool or spa mode. My pool technically has a spa, but it is a little 2 seat unit that is part of the main pool, and so the spa part of the heater is not hooked up to anything. If I want to heat the spa, I just set the valves so the returns empty into the spa instead of the pool. The pools is an 18x32 vinyl in ground, and the water temp is roughly 50-60 degrees right now. The pressure in my Filter when clean is about 10-15psi depending on what valves I have set where, and right now is about 12-17.

Now for the odd behavior. When I set the switch to Pool, and turn the temperature dial up, it reaches the point where it is supposed to ignite. I hear the gas come on, and I hear the buzzing that I assume is the ignitor sparking. About a second later I hear the whoosh of the gas lighting. So far so good. The problem is, about 1-3 seconds later, the buzzing stops, and the gas shuts off, putting out the flame.

If I turn the dial down and then back up again, it does the same thing, though it ignites faster this time. However, once again, when the buzzing stops the gas turns off. If I do it a few more times, eventually the fire will ignite correctly, with only a split second of buzzing, and the gas will stay on. The heater will then happily burn away my money heating the pool until I shut it off. The longest I have had it on so far was 3 hours, but it seemed to be working perfectly as best I could tell.

I am planning to burn it long enough at the start of this weekend to finally be able to get in my pool for the first time, but I wanted to see if you guys had any idea what could be causing this, and if there are any problems with letting it burn. It will heat the pool if I babysit it till it ignites, but it will not be able to light itself unattended to keep the temp up. Could it just be the coldness of the water/air causing some temp sensor to not think the unit is lit, and it shuts itself off?

Thanks again for the great advice.

btw here is a pic of the pool, so you can see what I am talking about with the "spa"

The water is now bluer and clearer then this pic, but you get the idea.



TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
It sounds like one of the safety sensors is either dirty or malfunctioning. The heater will turn off if it doesn't think there is a flame. Apparently the sensor that senses if the gas actually lit is not working quite right. Since it does work eventually, I suspect that it has just gotten dirty. If you can open up the burner and clean everything that might fix it.


LifeTime Supporter
Jul 27, 2007
Sahuarita, AZ
There is usually a water flow sensor that will turn off the flame if it doesn't have enough flow, but I suspect it would prevent the ignition from occurring in the first place if that were the problem.


Well-known member
Apr 22, 2008
Central Texas
Sounds like the same problem the furnace had at my last house... Look in the area of the flame, near the gas injector manifold, for what looks like a heavy piece of uninsulated wire that is in the flame path. It will be mounted in a ceramic insulator, with one wire attached. This is the flame sensor.

Carefully unplug the wire and remove the sensor. In the area where the flame touches it sand it with very fine sand paper to remove any oxidation. Just make it nice and shiny again. Reinstall and test. If the sensor was dirty, you'll have fire once again. :)

The wire actually generates a few milliamps of current when heated. Oxidation somehow impedes the process and the furnace control sees the lack of current as a no-flame condition and switches off the gas flow to prevent a gas explosion.