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I have a 3-zone baseboard radiant system with a 10-year-old Electro-Boiler EB-MO-20 with outside reset. System pressure is about 15 lbs. In mild weather the system works fine, with no particular noise beyond ordinary expansion sounds. In very cold weather when water temperature is high and all four elements are on, there is considerable vibration from the boiler that is transmitted through the radiators. Very noisy, very annoying. When the boiler hits its 185 degree high limit and the elements shut off, the vibration ceases instantly even with continued heat call. The circulator is completely silent in any conditions. I have tried turning the panel temperature select screw down but the boiler still heats to the 185 limit (unless I turn it to about '3'--then the water temp goes too low to heat the house). Any suggestions?