Heat Pump Malfunction? How to Tell Normal Operation from a Real Problem
Quick answer: many calls we get about a "heat pump malfunction" turn out to be normal operation: steam and a gurgle during a defrost cycle, air from the vents that feels cooler than a furnace's, a quieter system than you are used to, or an electric bill so low you assumed the unit was not running. Real malfunctions look different: the unit will not turn on, it short-cycles every few minutes, the outdoor coil is encased in ice that never clears, an error code is flashing, or the house is losing ground on a night it should hold. Before you call, check the breaker, the remote's mode and setpoint, and the filters.
Why it seems like a malfunction when it is not
A furnace heats air to 120°F or more and blasts it for ten minutes, then shuts off. A heat pump delivers air at 90°F to 105°F continuously and quietly. Hold your hand at a register and it feels lukewarm compared to the furnace you grew up with, yet the room holds 70°F all day. That is the system working as designed: steady, low-level heat with an inverter compressor modulating in the background instead of cycling.
The other common "problem" is the bill. We have had customers call because their first NYSEG bill after switching from propane was low enough that they thought the heat pump was not running. It was. Mitsubishi Hyper-Heat delivers roughly three units of heat per unit of electricity.
And the cold-weather myth: older heat pumps did lose their heating ability well above zero, which is why some people still assume a heat pump needs a furnace behind it in the Adirondacks. Mitsubishi Hyper-Heating INVERTER equipment delivers 100% of rated capacity at 5°F and keeps operating to -13°F, or -22°F on H2i Plus models. A system sized correctly for your home carries it as the primary heat. See heat pumps in cold weather.
Normal behaviors that get mistaken for malfunctions
| What you notice | What it is |
|---|---|
| Steam rising from the outdoor unit, a hiss or gurgle, indoor fan pauses for a few minutes | Defrost cycle. Below about 40°F frost forms on the outdoor coil; the system briefly reverses to melt it. Normal and automatic. |
| Water or a sheet of ice under the outdoor unit | Defrost meltwater. Normal, as long as the coil itself clears. We mount units on stands so this ice never blocks airflow. |
| Air from the indoor unit feels cool to the hand | Heat pump supply air is lower temperature than furnace air but continuous. Check the room thermometer, not your hand. |
| Indoor unit blows nothing for a minute after start | Cold-air prevention: the coil warms before the fan runs. |
| Outdoor unit runs continuously on a cold night | Inverter modulation. Continuous low-speed running is more efficient than cycling. |
| The "comfort number" on the remote does not match a thermometer | The unit senses at its own location; set it by how the room feels, or add an MHK2 wall thermostat. |
What a real heat pump malfunction looks like
- It will not turn on at all, or the indoor unit lights blink a code.
- Short cycling: starting and stopping every few minutes without reaching setpoint.
- Ice that never clears. A thick shell of ice over the whole outdoor coil that survives a defrost cycle means a defrost, sensor or refrigerant problem. Shut it off and call us.
- Losing ground. The room drops below setpoint on a night the system handled fine last year.
- Weak airflow from the indoor unit, often traced to a packed filter or a dirty blower wheel.
- Water dripping from the indoor unit: a blocked condensate drain.
- New or worsening noise: grinding, rattling or a loud buzz at the outdoor unit.
- Burning or electrical smell: turn it off at the breaker. See heat pump odors.
What to check before you call
The remote
Is it in Heat mode, not Auto, Fan or Dry? Is the setpoint above room temperature? Are the batteries good and is it pointed at the unit?
The breaker
Check the panel for a tripped breaker on the outdoor unit and the disconnect box beside it.
The filters
Pull them and look. A packed filter is the single most common cause of weak heat and ice. See filter cleaning.
The outdoor unit
Is it buried in snow or blocked by leaves? Clear it, then give it an hour.
Reset
Turn the system off at the breaker for five minutes, then back on. If an error code returns, note it.
Our online troubleshooter walks through these steps and tells you when to stop and call.
How we handle a malfunction
Do not open the equipment or attempt refrigerant or electrical work yourself. Call (518) 812-1958 or schedule a repair online. If your system has Wi-Fi control, our office can often read the error history through the Mitsubishi Comfort app and sometimes fix the issue remotely; one High Peaks customer had a temperature issue diagnosed and resolved "within minutes" without a site visit. For anything on site, our technicians carry common Mitsubishi parts on the truck, and Adirondack Shield members get $0 repairs and 24-hour priority service. We repair other brands too; see heat pump repair.
Frequently asked questions
Why is my heat pump steaming and gurgling?
That is a defrost cycle. Below about 40°F frost forms on the outdoor coil, and the system briefly reverses to melt it, producing steam, a hiss and a short pause in indoor heat. It is normal and automatic.
Why does the air from my heat pump feel cool?
Heat pump supply air runs around 90°F to 105°F, cooler than furnace air but delivered continuously. Judge by the room temperature, not by hand. If the room is not holding setpoint, that is a different matter.
My outdoor unit is covered in ice. Is that normal?
A light frost that clears each defrost cycle is normal. A thick shell of ice over the whole coil that does not clear is a malfunction: shut the unit off and call for service.
What should I check before calling for heat pump repair?
The remote's mode and setpoint, the breaker and outdoor disconnect, the indoor filters, snow or debris around the outdoor unit, and a five-minute power reset. If an error code persists, call us.
Talk to us
Have questions about your home? Call Adirondack Heat Pumps at (518) 812-1958, stop by the showroom at 15 Montcalm Street in Ticonderoga, or request a free in-home estimate. We serve Essex County, the Lake George and Lake Champlain shores, the High Peaks and Addison County, Vermont.