Thermostat says heat on but the house won’t warm up
If the thermostat says the heat is on and the house still sits a few degrees under the setting, the system is running but not delivering. The usual reasons are a clogged filter, a heat pump that’s struggling in the cold, a furnace that keeps shutting itself off, or simply a very cold night.
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From one of our jobs
A thermostat reading 66 with the heat set to 69
Right now: Pull the filter and look at it, then hold your hand over a vent. A gray filter or cool air at the vent, call before the night gets colder.
This one shows the heat running, the house at 66 and the setting at 69. On the first cold night that can be normal for an hour. Stuck there all day, something is holding the system back.
Feel the air at a vent. Warm and weak points at the filter or the blower. Cool or lukewarm on a heat pump points at the outdoor unit or the backup heat. A furnace that starts, stops and starts again is often a dirty flame sensor.
Quick answers
What people ask about heat that won’t keep up
Why is my heat running but the house is cold?
A clogged filter, a dirty flame sensor, a heat pump low on refrigerant or a failed heat strip are the common causes. Start with the filter.
Why is my heat blowing cold air?
On a heat pump, it may be defrosting for a few minutes, which is normal. On a furnace, the burners aren’t staying lit, and that needs a tech.
How long should it take my house to warm up?
A couple of degrees an hour is typical. If it never reaches the setting after several hours, the system is falling behind.
Should I turn the thermostat way up to heat faster?
No. The heat comes out at the same speed either way, and on a heat pump a big jump turns on the backup heat strips.
Who fixes heat that won’t keep up in Northern Virginia?
Call SwiftPro at (703) 997-9757. We repair furnaces and heat pumps that can’t keep up across Northern Virginia.
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SwiftPro Heating, Cooling & Plumbing
4230 Lafayette Center Dr N, Chantilly, VA 20151
44679 Endicott Dr, Suite 211, Ashburn, VA 20147
SwiftPro Plumber & Water Heaters
4200 Lafayette Center Dr, Suite N, Chantilly, VA 20151
Virginia Class A contractor license #2705192276