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Heat not turning on in the house

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Before you assume the heat pump itself has failed, work through power and the thermostat in order. Most no-heat calls that turn out to be simple are electrical, not mechanical.

Start with power, not the heat pump itself

Before you assume a mechanical fault, work through power in a fixed order: the thermostat display, the breaker panel, and the outdoor disconnect. A heat pump that gets no signal from the thermostat and a heat pump that gets no power look identical from inside the house. And one of those you can rule out in under a minute.

If the thermostat screen is blank, the fault is almost always electrical rather than mechanical. Check the breaker for the air handler or indoor unit first, since a tripped breaker there cuts thermostat power along with everything else.

Confirm the thermostat is actually calling for heat

Make sure the system is set to heat, not cool or off, and that the setpoint sits a few degrees above the current room temperature. Some thermostats need a moment after a setpoint change before they act on it. Give it a minute rather than assuming the request failed instantly.

If your thermostat has a separate emergency heat setting, switching to it and getting warmth is not proof the heat pump itself works. Emergency heat runs a backup source instead of the heat pump, so getting heat that way still means the heat pump side needs a technician.

A tripped breaker or disconnect

Heat pumps draw power through two separate places worth checking: the breaker for the indoor air handler, and outside, a disconnect box mounted near the outdoor unit. Either one can trip or get switched off without you noticing, especially after storm cleanup, yard work near the outdoor unit, or a recent power outage.

If a breaker trips again immediately after you reset it, stop resetting it. A breaker that trips repeatedly is reporting an electrical fault, not being oversensitive, and resetting it again risks damaging the equipment further.

Is the outdoor unit doing anything at all?

Walk outside while the system is calling for heat. A working heat pump should show some activity at the outdoor unit: the fan turning, a low hum, or at minimum a change from complete silence. If the outdoor unit sits completely dead while the thermostat calls for heat, the fault is usually at the unit itself, at the wiring run between the indoor and outdoor sections, or at the disconnect mentioned above.

Frost on the outdoor coil in cold, humid weather is normal and clears on its own through a periodic defrost cycle. What is not normal is a unit buried in ice that never seems to clear. Or one that stays silent through more than one heating call in a row.

A safety lockout you may not see

Many systems include a control board that locks the unit out after a set number of failed start attempts. That is a protection, not a fault in itself. If the system tried and failed to start several times in a row before you noticed, it may now be sitting in a lockout state. That state only clears after power to the unit is cut and restored, or after a waiting period set by the manufacturer.

Cutting power at the breaker for thirty seconds and restoring it can clear a lockout on some systems. Treat that as a one-time test, not a routine fix. A unit that keeps re-entering lockout has a real problem underneath, and resetting it over and over just delays finding it.

What not to do

  • Do not reset a breaker more than once if it trips again right away.
  • Do not open the outdoor unit's electrical compartment to check wiring, the contactor, or the capacitor yourself. A capacitor can hold a dangerous charge even with the power off.
  • Do not run the system on emergency heat for days at a time as a substitute for diagnosing the heat pump side.

When to call a licensed technician

If power checks out at both the breaker and the disconnect, the thermostat is confirmed to be calling for heat. And the outdoor unit still shows no sign of life, the problem is inside the equipment or its wiring. That is a licensed HVAC technician's diagnosis, not a homeowner one. Nothing past the disconnect is safe to test without the right equipment and training.

Frequently asked questions

My thermostat screen is blank. Does that mean the heat pump is broken?

Not necessarily. A blank thermostat screen usually points at a power problem, most often a tripped breaker for the indoor unit, rather than a fault in the heat pump itself. Check the breaker before assuming the equipment has failed.

Is it safe to just keep resetting the breaker until it stays on?

No. A breaker that trips again as soon as you reset it is reporting a real electrical fault. Resetting it repeatedly does not fix that fault and can make the underlying problem worse.

Sources

What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.

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