Had the customer turn the thermostat up. The circulator turned on and the temperature dropped to 120* and the burner did not turn on. Checked for power in the aquastat. “B1” for the burner had 120v but the burner was not running. Went to remove the primary and the burner started. The relay inside the primary control is intermittently pulling in. The primary control needs to be replaced. Replaced and tested. The system is operating properly.