Heat Pump Water Heaters: How They Work, What Fails, and Who Should Service Them

By David Quezada, owner of Four Roots Air Solutions, Loomis, CA | CSLB #1147036

Short answer: A heat pump water heater is a small refrigeration system bolted to the top of a water tank. It pulls heat out of the surrounding air and moves it into your water, which uses far less electricity than a standard electric tank. When one acts up, the cause is usually airflow, condensate drainage, the installation space, sensors, or the backup electric elements, and only sometimes the sealed refrigeration system. Because the heart of the unit is a compressor, coil, fan, and expansion device, the best person to diagnose it is someone with a refrigeration background who also understands the water side. That is the work Four Roots Air Solutions does every day.

Key takeaways

• Heat pump water heaters (also called hybrid water heaters) combine a heat pump with backup electric heating elements in one tank.
• Most service calls come from clogged air filters, dirty coils, blocked condensate drains, tight or cold installation spaces, failed sensors, or failed heating elements.
• A unit that keeps falling back to electric heat may still make hot water while quietly costing you money.
• The heat pump section is a refrigeration circuit. Diagnosing it well takes refrigeration experience, not just plumbing experience.
• We service major brands including Bradford White, Lennox, LG, Navien, A. O. Smith, and Rheem.

How a heat pump water heater works

A standard electric water heater makes heat with resistance elements, the same way a toaster does. A heat pump water heater moves heat instead of making it.

Here is the cycle, in plain terms:

1. A fan pulls room air across a cold coil (the evaporator). Refrigerant in the coil absorbs heat from that air.
2. A compressor squeezes the refrigerant, raising its temperature well above the temperature of the water.
3. The hot refrigerant runs through a condenser wrapped around or inside the tank, handing its heat to the water.
4. An expansion device drops the pressure, and the refrigerant heads back to the coil to pick up more heat.

It is the same cycle as an air conditioner or a refrigerator. The difference is where the heat ends up: in your water instead of outdoors.

Every unit also has one or two electric heating elements. Depending on the operating mode, those elements help during heavy demand, take over when the air around the unit is too cold or too hot for the heat pump, or run the whole show if the heat pump fails.

What the cool exhaust air means

Because the unit pulls heat out of the air, it blows out cooler, drier air. In a Sacramento Valley garage in August, that is a nice side benefit. In a small closet with no fresh air, the unit can end up recirculating its own cold exhaust, which hurts performance. That is why the installation space matters so much (more on that below).

Heat pump water heater brands we service

Heat pump water heaters have gone from a niche product to a mainstream one, and more manufacturers have entered the market in the last two years. These are some of the major brands we see and service in the field.

Bradford White AeroTherm Series G2

Bradford White’s AeroTherm G2 is the company’s most efficient hybrid model to date. It offers five operating modes (heat pump only, electric only, hybrid standard, hybrid plus, and vacation), app control through Bradford White Wave, and zero side and rear clearance so it can sit along a wall or in a corner. Its heat pump runs across a wide air temperature range and switches to the electric elements outside that range.

Lennox heat pump water heaters

Lennox entered the water heater market in 2026 through a joint venture with Ariston Group. Its heat pump models come in 40 to 80 gallon sizes, use a glass-lined steel tank, and can connect to the Lennox Home Comfort app on compatible systems. Because these are newer to the market, many homeowners and installers are still getting familiar with them.

LG Inverter Heat Pump Water Heater

LG’s heat pump water heaters use an inverter compressor, which varies its speed instead of simply running full speed or shutting off. LG rates its compressor to keep running in colder air than many competitors before handing off to the electric elements. Inverter drives add electronics that a technician needs to understand when diagnosing a “won’t heat” complaint.

Navien NWP500 Series (including the NWP500-65)

Navien, best known for tankless water heaters and boilers, launched the NWP500 Series in 50, 65, and 80 gallon sizes. The NWP500-65 is the mid-size model, with a stainless steel tank, a washable air intake filter, top and side water connections, a built-in condensate alarm, and five operating modes. It is one of the quieter units on the market.

Other brands

We also work on heat pump water heaters from A. O. Smith, Rheem, State, and others. For CO2 split-system water heaters such as the Sanden SANCO2 and A. O. Smith Voltex X, see our post on CO2 heat pump water heater service.

Brand and model names are used to describe the equipment we service. Four Roots Air Solutions is not a manufacturer-authorized service center unless stated otherwise.

The most common heat pump water heater problems

1. Clogged air filter or dirty evaporator coil

This is the number one maintenance item. Most units have a washable filter at the air intake, and a garage or laundry room puts plenty of lint and dust in the air. When the filter or coil clogs, airflow drops, the heat pump struggles, and the controls often give up and switch to the electric elements. Many units will throw an airflow or filter alert. Some will simply run up your power bill without saying anything.

2. Condensate drain problems

Pulling heat out of humid air produces water, just like an air conditioner. That condensate has to drain away. A clogged or kinked drain line, a missing trap, or a drain run uphill can back water into the unit and trip the condensate sensor, shutting the heat pump down. Left alone, it can also leak onto the floor around the tank.

3. The unit keeps running on electric heat

Hot water still comes out of the tap, so it is easy to miss. Common causes:

• The unit was left in electric or high-demand mode
• The surrounding air is outside the heat pump’s operating range
• A sensor, fan, or compressor fault has locked out the heat pump
• Airflow is restricted

The only symptom may be a higher electric bill. If your bill went up after a heat pump water heater was installed, or after a service visit, it is worth a look.

4. Not enough hot water or slow recovery

Heat pumps heat water more slowly than electric elements do. A tank that is undersized for the household, a mode setting that does not match how the family uses hot water, a failed upper or lower element, or a failing mixing valve can all leave you short. So can a heat pump that is not actually running.

5. Installation space that is too small, too cold, or poorly ducted

Every manufacturer lists a minimum room volume, an operating air temperature range, and rules for louvered doors or exhaust ducting. A unit squeezed into a sealed closet will cool its own space and lose efficiency. One with ducting that is too long, crushed, or poorly sealed will lose airflow. These are installation problems, and no amount of part replacement fixes them.

6. Sensor, control board, and fan failures

Temperature sensors (thermistors) on the tank, coil, and air inlet tell the control board what is going on. When one drifts or fails, the board makes bad decisions or shuts down with an error code. Fan motors and capacitors also wear out. Each manufacturer has its own codes and diagnostic sequence, and we follow them.

7. Sealed system problems

Less common, but serious: a refrigerant leak, a failing compressor, or a restricted expansion device. These show up as a heat pump that runs but does not heat, or a unit that trips on high or low pressure. Many manufacturers handle sealed-system failures through a warranty process, so the first step is a clear diagnosis that proves where the fault is.

8. Standard water heater issues

A heat pump water heater is still a water heater. Sediment, anode rod wear, a dripping temperature and pressure relief valve, leaking fittings, and expansion tank problems all apply. Hard water in parts of our service area makes routine flushing worth doing.

Why a refrigeration background matters

Water heaters have traditionally been the plumber’s job. A heat pump water heater changes that, because the part doing the heating is a refrigeration system.

David Quezada spent about 13 years in field HVAC before founding Four Roots Air Solutions, including commercial refrigeration work and three years installing transcritical CO2 refrigeration racks, some of the most demanding refrigeration systems in use today. Day to day, Four Roots services VRF systems, ductless mini-splits, and commercial refrigeration, equipment where diagnosing compressors, coils, fans, sensors, and electronic controls is the core of the job.

That background carries straight over to a heat pump water heater:

• Reading the refrigeration side. Knowing how a healthy system should behave makes it possible to tell an airflow problem from a sensor fault from a real sealed-system failure.
• Understanding inverter compressors and electronic controls. Newer units, like LG’s inverter models, use variable-speed compressors and electronic expansion valves, the same technology we work with on VRF and mini-split systems.
• Treating airflow and condensate as system problems. These are everyday HVAC issues, and they are the most common reasons a heat pump water heater underperforms.
• Looking at the water side too. Tank sizing, mixing valves, recirculation, and plumbing configuration all affect how the system performs. A good diagnosis checks both.

The result is a more accurate answer. Instead of replacing parts until something works, or replacing a whole unit that only needed a sensor or a clean coil, we find the actual fault and explain it.

What a service visit looks like

1. Listen to the complaint. When does hot water run short? Has the electric bill changed? What mode is the unit in?
2. Check the space. Room size, air temperature, louvers or ducting, and anything blocking the intake or exhaust.
3. Check the heat pump. Filter, coil, fan, condensate drain, error history, and heat pump operation using the manufacturer’s diagnostic procedures.
4. Check the tank and water side. Elements, sensors, relief valve, mixing valve, and plumbing configuration.
5. Explain what we found. You get a clear answer, whether it is a cleaning, a part, a settings change, an installation correction, or a warranty claim.

Frequently asked questions

How long does a heat pump water heater last?

Life expectancy depends on the brand, the tank construction, water quality, installation, and maintenance. Keeping the air filter clean, the condensate drain clear, and the tank flushed gives any unit its best chance.

How often should a heat pump water heater be serviced?

Check and clean the air filter every few months, more often in a dusty garage. A professional check of the coil, condensate drain, elements, sensors, and heat pump operation once a year helps catch problems before the unit falls back to expensive electric heat.

Why is my heat pump water heater making cold air?

That is normal. The unit pulls heat out of the room air and blows out cooler, drier air. If the room is getting too cold, the space may be too small or poorly ventilated for the unit.

Can a plumber service a heat pump water heater?

A plumber can handle the tank and water connections. The heat pump section is a refrigeration system with a compressor, coil, fan, sensors, and controls. Diagnosing that side well takes refrigeration experience.

My heat pump water heater shows an error code. What should I do?

Write down the code and check the owner’s manual. Some codes point to simple fixes like a dirty filter or a full condensate drain. Others point to sensor, fan, or sealed-system faults that need a technician. If the code comes back after clearing it, call for service.

Is it worth repairing, or should I replace it?

It depends on the age of the unit, what failed, and what the warranty covers. Many problems are cleanings, sensors, fans, or elements, which are well worth fixing. We give you the diagnosis first so the decision is based on facts.

Heat pump water heater not keeping up?

If your Bradford White AeroTherm, Lennox, LG, Navien, or other heat pump water heater is running short on hot water, throwing error codes, leaking, or quietly running up your electric bill, call a contractor who understands the refrigeration side and the water side. At Four Roots Air Solutions, we diagnose the whole system before recommending a fix.

Call (916) 664-4843 or request service from Four Roots Air Solutions to schedule a heat pump water heater service visit.

Based in Loomis, CA, and serving Sacramento, Placer County, and surrounding areas. Four Roots Air Solutions | CSLB #1147036