My Burham Steam Boiler showing high pressure on pressure gauge

East

I have my steam boiler changed about 10 years ago to  Burham gas fired power vent boiler (  IN5PVNI-M2), It never had issue till this year. 
First the boiler started banning noise, after flushing the system multiple times, it seems the noise has not yet came back.  
But we also notice the pressure gauge on boiler showing high pressure when starting the boiler ( needle approaching 30psi, pressure gauge is 1-30psi). 
But when we open one of the valve at the return pipe near boiler ( the radiator system does not have any pressure), but the needle of the pressure gauge still stays at 30psi.  If turn the boiler off completely, over time, the needle on gauge will eventually fails to zero. 
Our initial thought is the pressure gauge for the boiler malfunctioned. But I like to ask is it possible that the radiator system ( piping) has no pressure, but boiler still maintains pressure?  I am going to replace a pressure gauge tomorrow after the item comes, what else I should do to diagnosis what's really go wrong? How do I test my pressuretrol see if that also need a replacement?  
Talking about pressure gauge, can I use universal pressure gauge 0-30psi or I need one specific for steam boiler?

JUGHNE

Is that gauge on a pigtail with the pressure control?

If the pigtail has never been cleaned, it is certainly time.

If your boiler went near and above 15 PSI, the relief valve (which should be tagged for 15 PSI) would open. It would be a noticeable event.

What is your pressure control settings, look inside for a white wheel if a solid cover.

Pictures showing your control and gauge will help.

East

Jughne, thanks for the response. Attached is the actual pressuretrol shot. I ordered a pressure guage since last post and changed it today. Discovered the old one has some debries aroubd the connection. It might explained why pressure guage malfunctioned. 
But I am not sure how to test the presduretrol see if it still function normal? Do I need to change it?   One thing i noticed when I go to change the pressure guage today is the boiler water runs low. The water inside sight glass only about 1/3 left.  Two weeks ago when boiler starts making noise, and we started flushing/ skimming the boiler that is two weeks ago and water was filler to one inch from the top of the sight glass. It seems definitely boiler lost water but the auto fill did not kicks in to fill in water. I am not sure what to test next?   Pressuretrol or water auto filler ?  How to test them?   I heard people mention "low limit control", where is that?   Attached is my presduretrol and its current setting.  Any instruction or commebts are appreciated. 

East

BTW, last time, we checked pigtail, it seems not blocked.