MoM Vent Failures - First Fire Up for the Year

This has been happening the past three years. I fire up the boiler for the first time and let it run for a while to check out the system. Make sure the main vents open, make sure the radiator vents open, system heats evenly, etc.

For the past three years I've had a couple dead Maid O' Mist vents. This year it was two of them. I let the system run for a while and go around and check for even heat on the radiators. Two of the radiators were cold as ice.

Gave the vents a couple whacks…nothing. Took the orifice off the top…nothing.

Took the vent off and it wouldn't make any rattling noises when shaking. I put a couple "previously dead" spare MoM vents on and got the radiators back up and running.

Last year I boiled previous two years of dead MoM vents in vinegar and then water a few times to try and clean them out. Lots of junk came out and they rattled again so I kept them as spares. They are back in service and working for now.

This seems to happen every year…a couple dead MoM's. I'm considering changing to Gorton.

This happen to anyone else? My boiler runs great with no issues (other than being oversized) but it seems to keep happening.