Cleaned and checked gas boiler. When I turned up the thermostat boiler control would not bring on burners. When I turned knob for limit control setting burners came on! Water temperature was 45 degrees below limit setting. Boiler control should not have kept burners off. It is working properly now though. Boiler may need new control board. inspected heat exchanger & flue venting. Cleaned condenser coil. Checked voltage & amp draw of pump. I bled air from accessible radiators. tested system expansion rate. System expansion tank is waterlogged. I partially drained system and trained expansion tank. Bled air from radiators. Suggestions: boiler may need new control board if it continues to act up.