The owner of an older house off Main Street called because the boiler kept clicking on and off and the radiators never got fully hot. The boiler was maybe fifteen years old, feeding radiators that were likely original. Quick look first: the water line sat about two thirds up the sight glass and looked clean, with no surging. Good start. The pressuretrol, though, told the story.
The cut in was set at 1.5 psi, with a differential that let the boiler stop barely above that. So the boiler would build a little pressure, quit, wait a few seconds, and fire again. The radiators never had a full cycle to fill with steam. We dropped the cut in to roughly half a pound and the cut out under 2, then watched three full cycles.
Better, but not done. The boiler still reached pressure fast. So we totaled the radiators upstairs and down, measuring each one for EDR. The connected load came out well under the boiler's rating. An oversized boiler fills the pipes before the far radiators finish venting, builds pressure and shuts off. Giving the air a faster way out was the practical fix.
We installed a second Gorton style main vent at the end of the longer main and replaced two slow radiator vents in the back rooms. Cycles stretched out, the back bedroom finally heated, and the clicking stopped. We noted the settings and vent sizes on a tag at the boiler, and told the owner that any future replacement should be sized to the radiators, not the old plate.