Diagnostic guide
Heat pump not heating? Here is what is happening and what to do.
A heat pump that won't heat is most often caused by a frozen outdoor coil, a tripped breaker, a dirty filter restricting airflow, a refrigerant issue, or a stuck reversing valve. The first three you can check yourself. The last two require a tech. Don't run the system for long periods if it's not heating, you can damage the compressor.
Likely causes, ranked by probability
- 1
Frozen outdoor coil
Persistent icing prevents heat exchange. Often points to a defrost sensor or refrigerant issue.
Likelihood 30%
- 2
Tripped breaker or disconnect
No power reaching the outdoor unit. Check the panel and the disconnect box outside.
Likelihood 20%
- 3
Dirty filter restricting airflow
Forces the system into protection mode and reduces heat output.
Likelihood 20%
- 4
Low refrigerant
Slow leak reducing capacity. Requires diagnosis and recharge by a tech.
Likelihood 15%
- 5
Stuck reversing valve
The valve that switches between heat and cool modes is jammed. Requires service.
Likelihood 15%
What you can try first
- · Check the breaker and outdoor disconnect
- · Wash or replace the indoor filter
- · Clear snow and ice from around the outdoor unit
When to call us: Outdoor coil stays iced over for more than 45 minutes after defrost cycle, or the system blows cold air for more than an hour.
Our diagnostic process
We arrive within a one-hour window, inspect the system end-to-end, read any active error codes, test temperatures and pressures, and identify the actual cause. You get a written quote before any repair work starts. The $129 diagnostic fee is applied to any repair you proceed with.
Frequently asked questions
Is heat pump not heating dangerous?
Most causes of "heat pump not heating" are not immediately dangerous, but ignoring them can damage the system or raise repair cost. Outdoor coil stays iced over for more than 45 minutes after defrost cycle, or the system blows cold air for more than an hour.
Can a cleaning fix this?
Sometimes. Biofilm, dirty coils, and clogged drain lines often resolve after a deep clean. Mechanical or electrical issues require a diagnostic visit instead.
How much does diagnosis cost?
Our diagnostic visit is $129 flat, applied to any repair you proceed with. We will quote any repair before starting work.
Need a tech to take a look?
$129 flat diagnostic. Same-week scheduling across Vermont. Credited toward any repair.