Welcome! Here are the website rules, as well as some tips for using this forum.
If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Utica SFH4150WT oil fired base board..New Honeywell aquastat L7224U..High Limit set 180° with 10° differential...When a zone calls for heat furnace turns on and runs till the 180 limit..At about 175 it starts to make a knocking noise rising in sound and speed and goes on for about 30 seconds after high limit shut off then ceases..This started last year prior to new aquastat.. Noticed the boiler water temp will rise to about 190 in a few minutes and drop as zone uses the water eventually to the 170 start up.. I searched here and gleaned what I could..Went and checked expansion tank for heat and is hot only in top 1/4..Boiler pressure will go from 15 psi to 20 at max temp and then drop down as boiler cools..Oil Service says getting too hot and is boiling [like in an area]? Say to reduce temperature? I did reduce high limit to 175 and seemed to help some, as far as how loud the knocks are..Sorry for long post, tried to give as much info as I could..Thanks, Seb..