I have an H250 NG and when I light the pilot it goes out when I release the pilot button on the gas valve?

It is not a flame sensor. It is a pilot generator or sometimes it is called a thermal pile or thermocouple.
easy to replace...
loosen brass nut, with aluminum tube at gas valve, and take good notice here... Two wires follow along the tubing and are connected to two of three screws on top of gas valve - loosen and remove. then unsecure pilot assembly from under the burner tray. Pull out the pilot assembly as one unit along with the tubing.
Then either unscrew small retaining nut or just pull straight down and generator will slide out.

i would replace the whole pilot assembly. If not at least clean the pilot orifice!

look at the picture at the following site. Click on 'enlarge picture'

good luck.


Parts4heating com Teledyne Laars R0027600 Pool Heater Universal Pilot...

Power can be on just turn the room thermostat down .

If pilot stay lit, then thermocouple is working.
If pilot will light, then you have gas. If pilot goes out when pilot button is released, then thermocouple is next suspect.

Thermocouple tip must sit in pilot flame.
The pilot light heat applied to two different metals inside thermocouple causes small current.
The current travels back to gas control valve through copper line.
If the gas valve receive this current, then a magnetic switch stays open and allows gas into the gas control valve.
The magnetic switch is on the end of the red button you push down when lighting pilot. Essentially the red button is an override to the magnetic switch.
If the gas control valve does not receive the current, then the magnetic switch does not stay open when you release the red button.
When replacing thermocouple, note that it is not screwed very tight into the gas control valve. Finger tight + 1/4 turn. If it is overtightened, then the small thermocouple current shorts out against the gas control body.

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Maybe, but unlikely. The amount of gas that is released to the pilot is pretty small. I assume the heater is outside, where the slightest breeze would blow the gas away. I also assume you are having trouble lighting the pilot and you are wondering if maybe there is no gas, since you can't smell it? It may take a few minutes of holding the button down before the pilot will light, and once it does, you may not be able to see the flame in the light of day. If you wait until dark (or at least dusk) you should be able to see the flame of the pilot more easily. And don't forget to hold the button down for a minute or two after it lights to be sure the thermocouple has had time to heat up. If you release the button and the pilot goes out, you probably didn't wait long enough, but it will re-light easily. I hope you find this helpful. Good luck.

The power pile (pilot generator) is defective. It produces a milivolt signal to ensure to keep the gas valve open. If it goes bad, the valve thinks the pilot is out, even when you are holding the button down, so when you release the button, it shuts the gas off to prevent excess gas buildup and a possible explosion.

most likely you have a thermopile that has low output. it takes about 100mv to maintain pilot light

Small red button in the bottom left corner of the heater. Looks like the ignitor on some grills. Push it hard enough and it will 'snap' which sends the spark out at the pilot head.

Spider nest in the pilot assembly. You should be able to pull the pilot out, remove the pilot tube and orifice inside, and see and clean out the silk.If not, a new assembly is about $100 from a pool store. We sell them at www.arrowmotor.net

Make sure thermostat is set higher than water temperature. Make sure pump is running and water is flowing through unit. If gas valve is not opening then flame sensor or gas valve is bad.