GV-3 Series 1 boiler issue

Chris49601

I have a GV-3 Series 1 bolier that will not continue to run very long after it ignites.  It goes through the normal cylce and ignites and will run for up to 5 minuts of so and then the gas valve begin clicking loudly.  It will click once to several times and then shut down and restart the purge cycle.  I have tried to troubleshoot it myself and have not found anything that is causing it.  I did notice that if I tap the pressuer valve is will cause the valve to click and shut down.  I replaced the pressure switch with a new one and that resulted in the boiler shuting down immediately after ignition, so I put the old one back on.  I am trying to find someone in my area to look at but have not found anyone good yet  I suspect the valve but do not want to spend $300 on my limited knowledge.  Any help or suggestions woudl be appreciated.  Thanks