i had a call for no heat i went and the pilot was out. i relight the pilot turned the gas valve on called for heat system went on operation fine. after boiler cycled when it shutoff it also shut off the pilot. so i relit it again and did the process all over again and it shut the pilot off again can u please tell me why the pilot is shutting off when the system shuts down thanks

The pilot orifice is probably plugged up allowing to small a pilot lite. The small pilot lite is being snuffed out by the gas flames shutting off when the boiler shuts down.

Do a search on this site for pilot orifice cleaning.

There are a few other items that can also cause this problem but clean the pilot orifice first.

what are the other reason so in case that dosent work i know what to look for

There are a few other items that can also cause this problem but clean the pilot orifice first.
Post back when this is done.

i cleaned the orifice and still the same problem

Next I would replace the thermocouple which is next to the pilot and connects to the safety. Make sure the replaement has a good amount of pilot flame on it to create a strong signal. Post back with results. The thermocouple is kind of a long shot but while you are in there you might want to pull all the burners and clean them out also. Since I am not there I am trying to take the steps I would use if I were there but I cannot see the situation which makes it difficult to access the situation exactly.