Heat pumps, and the two things that go wrong with them

Most houses built here since about 1980 are on a heat pump. They are a good fit for this climate and there are exactly two failure modes that account for most of the complaints — both of them invisible from inside the house.

(706) 730-6094 Book a visit

How it works

The same machine, running both ways

A heat pump is an air conditioner that can run in reverse. In summer it moves heat out of the house; in winter it moves heat from the outside air into the house. A reversing valve decides which way round it is working.

Because it moves heat rather than making it, it delivers more heat than the electricity it consumes would produce directly. That is the whole argument for it, and in a climate with mild winters like this one it is a strong argument.

Failure one: back-up heat running when it should not

Every heat pump has electric resistance heat for the coldest days and for defrost cycles. It is expensive to run and it is completely silent, so a system running on it far more than it should costs money for months without anybody noticing.

Caused by a thermostat wired or configured wrongly, often after a smart thermostat was fitted
Caused by a refrigerant charge that is out, so the pump cannot keep up and the strips fill the gap
Caused by an outdoor unit that cannot breathe or a coil that is filthy
The usual symptom is a bill, which is the most expensive way to find out

Failure two: defrost behaving badly

In cold damp weather frost forms on the outdoor coil and the system periodically reverses to melt it off. That is normal and it is supposed to look alarming — steam, a change of noise, cool air indoors for a few minutes.

Defrosting far too often usually means a sensor, a control board or a charge problem
Never defrosting at all leaves a coil icing up until it stops working
Ice at the bottom of the unit can also be a drainage problem rather than a defrost one
A great many perfectly normal defrost cycles get reported as faults, and we would rather explain that than charge for it

Normal

Things a heat pump does that are not faults

This list exists because these four are the commonest reasons we are called out to a system that has nothing wrong with it.

The air from the vents is not hotA heat pump delivers a large volume of warm air rather than a small volume of hot air. It will feel cooler than a gas furnace does, at your hand, while heating the house perfectly well.
It runs for a long timeLong steady run times are how a heat pump is supposed to behave, and in this humidity long cycles are also what keeps a house dry in summer. Short frequent cycles are the thing to worry about.
It steams in winterThat is a defrost cycle finishing. It is meant to happen and it is over in a few minutes.
The outdoor unit runs in winterIt has to. In heating, the outdoor coil is where the heat is being collected from.

Servicing

What a heat pump service should include

A heat pump runs in both seasons, so it accumulates roughly twice the hours of a cooling-only system. It earns the attention.

Every visit

Filter changed, size recorded on the cabinet
Both coils inspected and cleaned as needed
Temperature split measured against the data plate
Static pressure measured, not assumed
Condensate drain, trap and float switch cleared and tested
Electrical connections, contactor and capacitor checked

Specific to heat pumps

Reversing valve operation confirmed in both modes
Defrost cycle initiated and watched through, rather than assumed
Back-up heat staging checked — when it comes on and why
Thermostat configuration read and confirmed against the equipment
Outdoor unit clearance and drainage at the base

All of it written down, so the next visit has something to compare against.

Book a service What is typical for your era? →

What we will not tell you about heat pumps

That a new one will cut a stated percentage off your bill. That it will pay for itself in a stated number of years. That the latest equipment is always the right answer. All three depend on your house, your tariff, what you are replacing and how the system is set up afterwards — and the last of those matters more than the badge on the box.

What we will say is that a correctly configured older heat pump frequently outperforms a new one that nobody set up properly, and that is not a sentence you will read on many contractors’ websites.