My house primarily uses minisplits for heat, but when it gets really cold things switch over to the old oil boiler for forced hot water baseboard heating. (Otherwise, the boiler is solely used as my source of hot water the rest of the year.) Things have been cold here lately, and I've been on oil for a few days. The house has been heating fine, but when I was in the basement doing laundry I noticed a clicking/chattering sound coming from the boiler. I took the cover off the box that was making the noise and, after some googling, it appears to be the "circulator relay" on the device (Honeywell Triple Aquastat Relay) that is chattering.

The house has two zones (one upstairs, one downstairs), but I haven't been able to tell if this behavior is occurring all the time or just when one of the zones is calling for heat. Regardless, the boiler does fire up. I can see the flame, the baseboards in both zones are warm to the touch, and I have hot water.

Does anybody know if this is fixable? I called my dad (retired electrician), but this is outside his wheelhouse. Is there something I can probe to see if the relay is getting the right voltage? Is the aquastat dying and needs to be replaced? If so, is this something that is DIYable (I'm reasonably handy).