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Boiler Troubleshooting, A Guide To Home Heating Boiler Repair

With our boiler troubleshooting guide, you can fix it yourself and save a lot of money. The average repair call will cost well over $100. With a little help, you can do it yourself and keep your hard earned money.

**NOTE** Only you can assess your ability to perform this task. This is a guide and cannot provide all of the details for every situation.

Proper maintenance will help you to avoid many of the common causes of boiler malfunction. Before you start troubleshooting, make sure you have performed the suggested maintenance. We will begin our boiler troubleshooting with the common gas fired heating boiler. This guide is for modern units that do not have a pilot flame burning constantly. If your unit has a standing pilot light, you should check to make sure it is lit. Then, you can use the rest of the guide but skip the part about the pilot lighting.

Gas Heating Boiler Troubleshooting

  • Start at the thermostat
  • 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.

  • Is the circulator pump running?
  • 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.

  • Check the temperature/pressure guage on the boiler
  • 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.

  • Do the main and/or pilot burners come on?
  • 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.

Combi Boiler Troubleshooting

We continue boiler troubleshooting with a look at combi boiler repair. We will check the unit in the central heating mode. You should begin by pushing the reset button on the unit. If the unit does not start then check the thermostat setting. If the setting is above the room temperature, check to see if the circulator is running. If it is not, check the fuse or circuit breaker for the unit. If you have power to the unit and it still does not operate, the problem could be with the thermostat, the circulator motor, or the units' control board. If the circulator starts, you can feel the unit's heating water outlet pipe to see if it is hot. If it is not hot, check that the unit's flue fan starts. If the fan does not start, the problem could be the water flow switch, the heating temperature sensor, flue fan motor, or the unit's control board. If the fan starts but the unit then locks out, the problem may be the flue temperature sensor. If the flue fan starts, does the burner ignite after a short delay? You should be able to hear the spark generator and the burner ignite. If it does not, the problem could be the spark generator, the gas valve, or the unit's control board. If the burner ignites, does it continue to operate? If it does not, the problem can be the flame sensor or the control board. In the dhw mode, the boiler troubleshooting procedure should be the same if water is being taken from the tap.

(NOTE: Most units have a minimum rate for the flow of water being taken from the tap, before the unit will operate. If the flow is not high enough the unit will not run.)

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