Gas and Oil Home Heating Furnaces - forced hot water - banging

I have a forced hot water heating system with oil-fired boiler up here in Acton, MA. Circulator fow one zone. Weather's been warmer up here, so thermostat / circulator haven't been running as much of late.

However, the boiler still fires to keep the water warm, and now when it does, the pipes around it (including the expansion chamber and flow check) start vibrating (about 10 Hz?) and banging, and the PSI reading on the boiler seems to vibrate back and forth. When the boiler shuts down, the vibrations stop.

I turned down the boiler temp and now the vibrations are less severe, but still happen. I checked for / drained air from the registers but found none anywhere.

What's going on with my heating system? Do I need to inspect / replace / tune the expansion chamber, flow check, boiler settings ... ?

Thanks, - J

What's your boiler temp, and pressure?

And when was the last time you had service?

(I am guessing the fire liner is gone, and you may have a hot spot)

Pressure is 20psi.

Temp was about 210, boiler setting was 180 low - 200 hi. I turned down the settings to 160/180 and now temp is about 190 and the vibrations are less severe but still there -- figured its less stress on the system this way.

Try bleeding air out of the system.