Heat Pump Blowing Cold Air – Why Is My Heat Pump Not Heating?

You have a heat pump blowing cold air when it should be heating.

What’s the trouble? Why is the heat pump not heating?

There are 7 common causes of a heat pump blowing cold air in winter when it should be making your home warm and cozy.

Heat Pump Not Heating: Problems and Solutions

Here are the most common reasons a heat pump doesn’t heat. They’re generally listed from most to least likely to be the problem, but every situation is different.

Low Refrigerant Charge – and a Refrigerant Leak

Refrigerant carriers heat from outdoors to indoors when your heat pump is in heating mode. Two refrigerant lines make a circuit between in indoor and outdoor coils.

One line carries hot refrigerant from the outside coil for the heat to be dispersed through the indoor coil. The other carries refrigerant back outside after it has dumped its heat.

If the system is low on refrigerant, it can’t collect and carry sufficient heat indoors.

New Units: Now, if the unit was just installed, then its possible the heat pump mechanic didn’t put enough refrigerant into the system.

If that’s the case, then the mechanic didn’t test the system before leaving. That’s a major fail! However, it’s not a common one.

Old Units: When low refrigerant is the cause of the heat pump not heating, it is a refrigerant leak in 95% of the cases.

The Low Refrigerant Solution


The HVAC technician must first locate the leak – usually a corroded fitting or damage to the refrigerant line. Once the leak is repaired, the system can be charged (filled) with the proper amount of refrigerant, and it should start bringin’ the heat!

This video shows an HVAC technician first considering a defrost problem (see below) before determining that the indoor coil is leaking refrigerant.

Depending on the cause of the leak, the repair will range from $200 to more than $600.

Dirty Outside Coil or Cabinet

Heat from the outside air is captured by refrigerant in the outside coil. The hot refrigerant is circulated inside.

When air can’t get to the outdoor coil, the refrigerant can’t pick up sufficient heat to warm your home.

Why is the coil and/or dirty? Grass clippings and blown dust are the most common reasons, but there could be any number of causes.

The Solution to a Dirty Heat Pump

The coil and cabinet need to be cleaned.

When outdoor temperatures are freezing, a moderately stiff bristle brush is ideal for brushing dirt and debris off the cabinet. Once the cabinet is removed, you can brush the coil.

Note on Trane and American Standard heat pumps: Those brands have a unique Spine Fin coil with rows that look like bottle brushes. Caution must be taken when cleaning these coils to prevent damage.

Pros typically spray on a cleaning solution, let it sit for 10-30 minutes, and hose it off. They might have alternative methods in freezing weather.

Call a heat pump company for the safe, effective cleaning of a Spine Fin coil.

What You Can Do

When the weather isn’t freezing, get in the habit of hosing away grass clippings and dust/debris from your heat pump cabinet and coil after cutting the grass. Take care not to soak the wiring. This video shows how to use gentle water pressure to clean a coil

 

Use a gentle brush on stubborn debris.

Heating and cooling companies clean coils as part of a maintenance service. Depending on how comprehensive the service is, the cost will be $80 to about $200.

Dirty Air Filter

Sometimes an air filter gets so dirty that it won’t let much air through it.

Even if the heat pump is heating like a champ, good airflow is required to disperse the heat.

Changing a Dirty Filter

The air filter is in your air handler or furnace. Remove the cabinet, slide the filter out of its slot, and replace it. More information about air filter, check our article: Central AC Filter Buying Guide.

What if you don’t have a replacement filter? Take the old one outside and brush it off with a nylon brush or your hand. Sometimes the dust layer will come off like lint off a dryer filter. Give the filter a gentle shake (stay upwind of it). If a lot of debris comes off it, the filter should allow enough airflow until you can get a new one.

If it’s really dirty and you can’t get much debris off of it, your heat pump system will be OK without a filter for a few hours to a day. Get a new one and install it at your earliest convenience.

Buildup of Ice and/or Snow

Heat pumps aren’t as common as furnaces in the North where snow and ice are common.

But if you’ve got one and the snow has been flying and/or it is bitter cold, this could be an issue.

Clearing Snow and Ice

Shovel snow away from your heat pump cabinet. Gently chip away ice on the cabinet.

Thawing an Icy Coil

As the outside coil collects heat and sends it indoors, the coil gets very cold. It’s common for frost to build up.

What about heat pump defrost mode? That’s a good question. Most heat pumps sense when the outdoor coil is iced, and they switch to defrost. And defrost mode pulls heat from inside to melt the ice on the outdoor coil. Yes – that’s right. It switches to AC mode for a short time to defrost the coil.

If your unit has a defrost mode, but it isn’t working, then the defrost timer that controls how long it runs in defrost mode might be bad. It’s also possible its circuit board or one of its parts has failed. These are usually jobs for an HVAC tech to diagnose and repair.

Before you call an HVAC pro, you might try switching to AC mode for 20-30 minutes to see if that will defrost the coil. If it does, switch back to heat mode, and you might get heat.

It’s a short-term fix. The defrost will have to be checked. But it might get you some heat while waiting for the repair technician.

Bad Reversing Valve

The reversing valve changes the direction of refrigerant flow when you switch modes at the change of the season:

  • AC mode circulates the refrigerant to capture heat inside and dump it outside.
  • Heat mode does the reverse – and it takes a functioning reversing valve to do the job.

Replacing the Reversing Valve

A heat pump blowing cold air in Heat mode might not be moving heat inside. It might still be moving heat outside since the reversing valve hasn’t switched. This means it is air conditioning your home!

This is a pro repair. The cost could exceed $500.

Auxiliary Heat Isn’t Working in Extreme Cold

Is the weather much colder than it typically gets for your climate?

If yes, this could be your problem.

Most heat pumps are outfitted with heating coils in the air handler. They are also known as heat strips or “strip heat.”

From 5kW to 20kW, these heaters are designed to provide auxiliary heat in extreme cold and emergency heat when the heat pump isn’t making any heat.

Heat pumps are sized from 18,000 to 60,000 BTU/hour based on many factors – and climate is one of them.

If the temperature outside is 20+ degrees colder than it usually gets where you live, your heat pump might not be big enough to heat your home in that kind of weather.

Backup Heat: Value and Failure

That’s where the heating coils prove their worth. They make up the difference to keep your home warm until temperatures become more seasonal.

A heat pump blowing cold air in the coldest winter temperatures could mean the auxiliary heat isn’t working. The heater(s) probably need to be repaired or replaced. Cost will range from $125 to $400.

Tripped Circuit Breaker…or Worse

If your heat pump isn’t running at all, it’s not getting power.

Check both the small circuit box outside your home near the heat pump and the circuit for your air handler in the large electrical panel.

Checking Breakers

Turn the breakers to the ‘off’ position and then back to the ‘on’ position. If the breakers are on, but the system won’t start, then the problem is best diagnosed by an HVAC pro with electrical testing equipment.

If it comes on…

You Might Not Be Done Yet

Why did the circuit trip?

A dirty filter is a common cause. The system is working too hard to push air around, it heats up and the circuit trips. A buildup of ice and snow could be the cause of overworking too.

Check those issues. If they’re not a problem, and the circuit trips again, call your heat pump company.

If it doesn’t come on, it could be that the control board for the heat pump has failed and needs to be replaced. That’s often a worst-case scenario with a cost of $250 to $500.

Is it Time to Replace your Heat Pump?

If your heat pump is getting old or has already had major repairs, discuss the pros and cons of repair vs replacement with a heat pump company.

Our Heat Pump Buying Guide will help you prepare for that decision.

It might be time to stop spending money on the old unit and get the dependability and higher efficiency of a new heat pump.

If a heat pump contractor suggests a new unit, they might be trying to save you money.

Does that seem counterintuitive?

Consider how some money-hungry contractors think: They’ll be happy to bill you for several repairs over the next few years until you finally decide it is time for a replacement. Then, they’ll be first in line to get that job too. This is a well-known trick of the trade.

Replacing your heat pump should be considered if:

  • It is 15+ years old, or
  • It is out of warranty and has been chronically problematic

We recommend you discuss this option with several heat pump companies. If you want free estimates to compare repair and replacement costs from some of the top installers in your area, there is no obligation for using our Free Local Quotes service.

The contractors are prescreened, licensed and insured. It’s a quick, no-hassle way to discuss your options with proven pros.

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