How to Troubleshoot an Utica Boiler Model 125-AGB


The Utica 125-AGB is a cast iron gas-fired, forced-hot-water boiler. The boiler has a heating capacity of approximately 104,000 BTU per hour with three burners and a total water content of over 5.5 gallons. The boiler should be cleaned and inspected annually by a service professional to help keep it working well, but if problems arise between inspections, some troubleshooting might be required.

Things You'll Need

  • Heavy paper
  • Soft brush
  • Calculator
  • Light the Utica boiler if power is lost and the furnace is not operating. Smell around the boiler first for gas and stop immediately if you detect a gas odor; then turn off the boiler, leave the house and call your gas company. Continue if you do not smell gas. Push the gas control knob in, turning it to “Off.” Wait five minutes and then smell again for gas. Follow the above directions if you smell gas or turn the gas control knob to “Off” if there is no smell of gas. Move the main boiler power switch to “On” and set the boiler thermostat to the desired hot water setting.

  • Take off the protective cap on the pressure regulator if the boiler has power but no pilot light. Turn the adjustment screw clockwise gradually to increase the input. Note the input rate on the boiler gauge and then look at the gas company heating value plate to find the input rate. Divide the input rate by the heating value, which equals the cubic feet of gas required per hour. Turn off all other gas appliances in the home and watch the gas flow through the meter for two minutes. Multiply this number by 30 to get the hourly rate. Adjust the gas input screw as needed to meet this hourly rate.

  • Clean the boiler flue passageways if the boiler is not heating water properly. Open the draft relief opening and look for soot on the flue gas passageways with a mirror and light. Disconnect power if there is soot visible and let the boiler cool. Lift up the burners from the manifold orifices and then pull the burners out. Remove the vent pipe from the draft hood and take the top jacket panel off. Loosen the nuts each side of the combination flue collector and the draft hood. Hold a sheet of heavy paper over the base bottom and use a brush to bring the soot down from the flue passageway. Keep the paper in place and clean the boiler castings. Don’t leave any chips in the passageway. Reassemble once the soot is removed.

  • Increase the pilot flame by taking off the pilot adjustment cover screw cap and rotating the screw counterclockwise. Decrease the pilot flame by turning the adjustment cover screw clockwise.

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