Furnace Won't Turn On? 6 Things to Check Before You Call
The first cold night of the season is when many furnaces refuse to start. Before you schedule a service call, a few simple checks can sometimes get the heat running again in minutes. Here are the six we recommend, in order, and when to stop and call a professional.
1. Check the thermostat
Make sure the thermostat is set to Heat, not Cool or Off, and that the set temperature is several degrees above the room temperature. If the display is blank or dim, replace the batteries. For smart thermostats, confirm the schedule or an away mode is not overriding your setting.
2. Check the breaker and the furnace switch
Look for a tripped breaker labeled furnace or HVAC in your electrical panel and reset it once. Also check the service switch near the furnace, which often looks like a standard light switch. It is easy to turn off by accident. If the breaker trips again, leave it off and call us.
3. Replace a clogged filter
A badly clogged air filter can cause the furnace to overheat and shut itself off as a safety measure. If the filter is gray and caked with dust, replace it and give the system a few minutes to reset.
4. Look at the pilot light or ignitor
Older furnaces have a standing pilot light. If it is out, follow the relighting instructions on the furnace label exactly. Newer furnaces use an electronic ignitor, and you should hear a click or see a glow within a minute or so of the furnace starting. Do not attempt to relight anything if you smell gas.
5. Check the condensate drain on high-efficiency furnaces
High-efficiency furnaces produce water that drains through a small line or into a condensate pump. If that line clogs or the pump fails, a safety switch shuts the furnace down. Water around the base of the furnace or a full pump reservoir is a common sign.
6. Make sure vents and returns are open
Blocked supply vents or return grilles restrict airflow and can trip safety limits. Move furniture, rugs, and stored items away from vents and make sure the outdoor intake and exhaust pipes on high-efficiency furnaces are clear of leaves, snow, and debris.
When to stop and call
You smell gas. Leave the house and call your gas utility from outside.
Your carbon monoxide detector sounds.
The breaker trips a second time.
The furnace starts, then shuts off again after a few minutes.
You hear banging, grinding, or squealing from the unit.
Nothing above solves the problem.
A furnace that starts and then shuts off is often a dirty flame sensor or a safety control doing its job, and both are routine fixes for a technician. An annual tune-up catches most of these issues before the cold weather arrives.
Family Heating & Cooling is a family-owned company based on Penn Street in Hellertown, serving homeowners across the Lehigh Valley, Bucks, and Northampton counties. Call (610) 421-9885 or request service on our website. We answer 24/7.
