How to Troubleshoot a Furnace Boiler Assembly

Look at the boiler's thermostat to make sure it is set to a temperature higher that the house's inside temperature. If it is lower, turn it up and see if the boiler fires up.

Go to the boiler in the utility room and look at the water gauge on its side. Make sure the boiler's water lever is between the necessary indicated levels for operation.

Listen to the circulator pump, located on the distribution pipes, to check if it is operating. Place your hand on its motor case. If it is hot, this indicates it has been running. If the pump is not on, check that the breaker in the electrical distribution box is turned on. If the pump is very hot to the touch, contact a qualified technician to determine the problem.

Look at the boiler's temperature/pressure gauge to make sure they are in the normal range. If both are in the correct range there maybe air in the boiler's pipes that needs to be released. Older systems required manually releasing the air by opening the air-eliminator valves. Newer systems have automated this process.

Check whether the vent dampener is open. Then verify that the inducer fan is running. If not, shut down the electrical breaker and then turn it back on a few minutes later. Check if the problem is corrected.

Check if the pilot light is on or ignites on start-up. If the vent dampener is open or inducer fan is working, and the pilot light is inoperable, the exhaust vent maybe obstructed.

Make sure the pilot light starts then goes out. This is evidence that the pilot assembly is dirty, the flame sensor is inoperable, the thermocouple is broken or the boiler's control unit is damaged.

Confirm if the boiler's burners ignite. If they do not, the gas valve is most likely broken. If they do ignite, but shut down quickly, contact a qualified technician to repair the boiler.