How to Troubleshoot a Boiler Furnace That Keeps Heating After Thermostat Is Shut Off

Reset the boiler by either hitting the reset button or by shutting off the breaker it runs on and turning it back on after 30 seconds. This often corrects malfunctions, but if the thermostat itself is failing, the fix is temporary at best.

Inspect the thermostat for any loose wiring or signs of burnout. If the thermostat has a digital display, look for error codes and verify that the thermostat is getting power. A loose connection or system error results in the thermostat not functioning properly and it likely needs replacement.

Wipe any visible dust on or around the thermostat off with a soft paintbrush. Accumulated dust interferes with thermostat operation and could result in the furnace running even when you think the thermostat is off.

Check the thermostat batteries, if you have a wireless system. Most thermostats require AA lithium batteries. If you used alkaline batteries, the power drains quickly and the thermostat might not be communicating with the furnace.

Clean all the furnace filters in accordance with the instructions for your particular model. Some models don't have cleanable filters and you need to replace them entirely. Old or dirty filters can cause erratic behavior in boilers and this can contribute to the thermostat problems.

Close the gas-shutoff valve to your boiler if you smell gas in the room. Ventilate the room and notify the gas company because your system likely has a leak that requires immediate repair.

Call a repair technician if you still have problems. A technician helps ensure the boiler operates safely and may replace the thermostat or other faulty components to correct the problem.