Gas Heating Boiler Troubleshooting
- Start at the thermostat
- Is the circulator pump running?
- Check the temperature/pressure guage on the boiler
- Do the main and/or pilot burners come on?
The first step is to check the thermostat. If you have a zoned system with several thermostats throughout the house, you will want to go to the main one. Ensure that it is set above the actual room temperature. If it is not a digital model, you must ensure that it is level and you may want to consider replacing it.
Next, you should go to the boiler and see if the circulator pump is running. You should feel the motor with your hand to see if it is hot. If the pump is not running and it is cool, check the breaker that supplies power to the boiler. If the motor feels very hot, the problem could be the run capacitor, the motor, or the pump itself could be locked up. If it is cool and the breaker is on, the problem could be the thermostat or the circulator relay.
If the circulator is running, continue your boiler troubleshooting by checking the temp/press gauge on the boiler. Most of the gauges will have a red line and the temperature/pressure reading should be above zero but less than the red line value. If the temperature and pressure is normal, there is probably air in the system. This is common on systems with the old style of manual air eliminators. You can easily replace the old manual type with modern, automatic, float type air eliminators. If the temperature and pressure are abnormally low, check to see if the vent damper is open and/or the inducer fan is running. If not, shut off the breaker to the unit, wait a couple of minutes and then turn it back on. If the damper does not open and/or the inducer doesn't start, the problem could be the boiler control or the aquastat.
If the vent damper is open and/or the inducer fan is running, does the pilot ignite? If the pilot does not attempt to light, the vent pipe could be blocked. If the pilot lights but does not stay lit, the pilot assembly could be dirty, the flame sensor could be dirty, the thermocouple could be bad, or the boiler control could be bad. You can use our guide to clean the pilot and sensor as well as to see how to replace the thermocouple. After the pilot is lit for a few seconds check to see if the main burners come on. If the main burners do not come on, the boiler control or the gas valve could be bad.