Boiler intermittently dropping water temp

njgallus

I have a Weil McLain He-6 boiler and it's not keeping up with my thermostat. It's running fine every 3-4 cycles but then it will still be calling for heat but won't keep the water temp above 140. It'll keep dropping down to about 90 degrees and then fire up finally and heat back up to 180. It's able to keep the house at about 65 deg when it's real cold but the thermostat will be at 68 so it's not keeping up. The green power light and the red pressure switch light are also blinking when the temp drops below 140 but otherwise on the other cycles it's running normal no lights are blinking. I've had techs out and they can't seem to figure out what it is. I've replaced the circuit board and the pressure switch already and neither have solved it.

I do have an inducer motor that is making slight noise/rattle when starting up and slowing down on shutoff but it's not a lot. Not sure it could be the motor failing to start sometimes or not. If I do a hard restart by turning power off and on it always starts firing up and goes through a normal cycle and heats back to 180.

Any thoughts or advice would be appreciated, thanks!