The pilot light is on, but the heater is not lighting. there is not heat going into my pool.

I don't know if there is a pilot light, spark ignitor or thermal ignitor. I would determine by inspection what kind it has. If you open the front cover you will find a gas valve. It can be identified by following the gas pipe that enters the side of the heater and attaches to the gas valve. If the valve has a control knob on it that has an off, on and pilot position then it is a pilot type. If this control is not on the valve then the unit includes an automatic ignitor.

To light a pilot equipped system place the knob in the pilot position, push it down, and use a flame to light the pilot. If you hear gas flowing from the pilot but it won't light then there is air in the line and it needs to be purged. Holding the pilot lighting valve down long enough will purge it but may take a long time. Periodically you can check it by trying to light it. If it lights watch it for a while before trying to turn the heater on to make sure it is fully purged. Once the pilot is stable and the thermocouple is heated the pilot valve can be released and it should stay lit. If not, try again.

Don't get down and look into the burners while you are trying to start the system because it could flame out and burn your face. If you turn on the heater again then the gas valve should come on and the burner should light. You can usually hear a loud snap when the gas valve come on. You should then hear the gas flow to the burner. If the burner doesn't light you should be able to smell the gas. If it lights exhaust will be coming out of the vents in the top of the heater.

I am sure you will have more questions so please respond with them. I hope this helps.

If your pilot light is lit, then you do have some gas flow, so it is probably the thermocoupler (the part heated by the pilot light) that is not telling the gas valve to open the main line. Sometimes it is just a case of residue on the thermocoupler that is not letting it get up to temperature and sometimes it has been knocked out of alignment and the pilot light is not putting direct heat on it.

A cleaning with steel wool (don't overdo it) would take care of the residue, and you can GENTLY move the thermocoupler back over the pilot flame. If neither of that helps then replace the thermocoupler.

If you have a pilot that need's to be lit you turn your gas valve to pilot and hold it down while you light the pilot and keep it down for 30-40 seconds to let the thermopile heat up enough to hold the gas valve on by itself. Then turn the gas valve to on.
Most heaters now will have an electronic ignition for the pilot or a hot surface ignitor. If you have power going to the heater then you have one of these heaters.
Let me know how you do. If it is one of these we can go further. Good luck.

millivolt heaters generate their own power from the flame on the pilot max is usualy 750 millivolt, check all connections clean and secure.
Mmake sure the pilot is lit

My problem has been solved. A friend looked at it and discovered that I have a short in one of the wires. Thank you for your quick response in this matter.

Replace the thermocouple that the pilot light heats up to keep the gas on.

you would have a a code that says that you pilot is dead, if failed to ignite, clean the heater to supply gas to headers

check pressure switch for proper adjustment and make sure filter is clean so system pressure is normal