General information about how these parts fail and how a diagnosis is confirmed. Your system may differ, and nothing here replaces someone measuring your equipment. We are an independent contractor and not affiliated with any manufacturer.
What the part actually does
It is the thing that makes a heat pump different from an air conditioner, and it has a cheap part attached to it that fails far more often than it does.
It reverses the flow
It is what lets one machine both heat and cool, by switching which coil is doing which job. It is the defining component of a heat pump.
The coil on it is a separate, cheap part
An electrical solenoid coil tells the valve when to switch. It fails far more often than the valve body and costs a small fraction. It does not require any brazing.
One thermostat setting controls it
A single wire tells it which way to run, and different manufacturers energise it in opposite modes. A thermostat configured for the wrong convention makes a perfect heat pump run backwards.
Defrost looks alarming and is normal
In winter a heat pump periodically runs in reverse to melt ice off its own outdoor coil. Cool air indoors, steam outdoors, outdoor fan off. It is meant to do that.
What is actually going on
One thing that can create the fault it is meant to find
This is a specific and known problem.
Never let anyone hit the valve to free it
It can cause the exact failure being diagnosed
The trade press states it plainly: never strike a reversing valve with a hammer or a wrench. Mechanical force can crack the seats or damage the slider inside, creating the internal leak that was not there before. If somebody taps the valve and then tells you it has failed, that is worth being sceptical about.
Check the settings before anything
The most common cause of a heat pump running backwards is not a broken part.
Is the thermostat on HEAT rather than EM HEAT?
Emergency heat bypasses the heat pump entirely
It runs the backup only, which is expensive and feels wrong. It gets left on by accident constantly.
Was the thermostat changed recently?
This is the big one
Different manufacturers energise the reversing valve wire in opposite modes, and a new thermostat has a setting for which convention yours uses. Set it the wrong way and the system does exactly the opposite of what you ask, reliably, with nothing broken. If the problem started right after a thermostat swap, that is almost certainly your answer and it is a settings change.
Is it winter, and is the unit steaming?
Then it is probably defrosting
Cool air from the vents, steam outside, outdoor fan stopped. It lasts a few minutes and then normal heating resumes. Homeowners report this as stuck in cooling every winter.
Listen when you switch modes
There is usually an audible clunk
Switch from heat to cool at the thermostat and listen at the outdoor unit. A whoosh or a clunk means the valve is shifting. Nothing at all is worth mentioning when you book.
What a proper diagnosis involves
And why one specific confusion is expensive in both directions.
The solenoid coil, first
Cheap, common, and no refrigerant work
A failed coil means the valve is never told to switch. It is a fraction of the price of the valve and a fraction of the labour.
The wire and the defrost board
Whether the signal is even reaching the coil
No signal produces the same symptom as a dead coil and a stuck valve.
The refrigerant charge
Low charge mimics weak heating and weak cooling
It looks like a valve that is not fully shifting, and it is a completely different repair.
Separating the valve from the compressor
These two mimic each other precisely, and this is the expensive confusion
Manufacturer literature admits that on a single phase system, if the compressor starts but the pressures do not split, it is either the reversing valve or the compressor — the standard test cannot tell them apart. There is a proper method involving a magnet and a pump down. Getting it wrong in either direction is a four figure mistake.
Four things that look like a failed reversing valve
- The thermostat configured for the wrong convention. The most common cause by a distance, especially after a thermostat has been replaced. It is a setting, not a repair, and it takes minutes for someone who knows where it lives.
- The solenoid coil rather than the valve. A separate, inexpensive part that fails much more often than the valve body and needs no refrigerant work at all. It should always be eliminated first.
- A normal defrost cycle. Cool air, steam and a stopped outdoor fan in winter is the system working. Worth ruling out before anyone is called.
- Backup heat hiding the problem. On a system with electric backup, a valve problem can go unnoticed for weeks because the strip heat keeps the house warm. You find out from the power bill rather than from the temperature.
The coil and the valve are two very different decisions
If it is the solenoid coil, fix it — it is inexpensive and straightforward. The valve body itself is another matter entirely. Replacing one means recovering the refrigerant, cutting the old valve out, brazing four connections in a confined cabinet while keeping the new valve body from overheating, fitting a new drier, pulling a deep vacuum and recharging. It is labour heavy and skill heavy. On an R-410A heat pump past about twelve years, that job frequently lands in the same neighbourhood as replacing the outdoor unit, so ask for both numbers written down. On an older R-22 system it rarely makes economic sense — and that is about cost, not legality. There is no requirement to replace an R-22 system; the rule is only that the refrigerant must now come from recycled or reclaimed stock.
Heat pump running backwards?
Check the thermostat setting first. If that is not it, book a visit and we will start with the coil.
Book a Diagnostic Visit60 seconds online · or call (206) 486-6373
How it works when you book
- 1
Tell us what you were quoted, or do not — both work Some people would rather we came in cold. We diagnose it ourselves either way.
- 2
We measure it and show you the reading The number off the meter and the number printed on the part. If those two do not disagree, the part is not the problem.
- 3
You get the price in writing before anything starts Itemised, and you approve it. If the honest answer is that nothing needs replacing, that is what you get.
Our service areas
We run out of Covington and cover the greater Puget Sound area.
King County
Covington, Kent, Renton, Maple Valley, Auburn, Federal Way, Des Moines, Enumclaw, Bellevue, Issaquah, Sammamish, Bothell
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Tacoma, Puyallup, Lakewood, Sumner, Bonney Lake
Snohomish County
Lynnwood, Everett
Not on the list? We cover the greater Puget Sound area around our Covington base. Book it and a technician confirms within 1 business hour.
Why homeowners hand it to us
- You approve the price first. Upfront quote before a single screw turns.
- We answer 24/7. Book in a minute, hear from a technician within 1 business hour.
- 500+ jobs done by 4.9★ rated, professional technicians.
- Fixed right, guaranteed. If it’s not right, we make it right.
Quick answers
My heat pump blows cold air when set to heat. Is the valve stuck?
It might be, and check two cheaper things first. Is the thermostat on HEAT rather than EM HEAT, and was the thermostat changed recently? A new thermostat set for the wrong reversing valve convention makes a perfect system run exactly backwards. Also, if it is cold outside and the unit is steaming, that is a defrost cycle and it is normal.
What is the difference between the coil and the valve?
The coil is the electrical part that tells the valve to switch. It is inexpensive, it is a separate item, and replacing it involves no refrigerant work. The valve is the mechanical body the refrigerant flows through, and replacing that is a major job. They fail at very different rates and cost very different amounts, so it is worth knowing which one you have been quoted.
My outdoor unit is steaming and the fan has stopped. Is it broken?
Almost certainly not. That is a defrost cycle: the system runs backwards briefly to melt ice off the outdoor coil, and the fan is off deliberately while it does. It looks dramatic the first winter and it is the system working properly.
Can a reversing valve be repaired rather than replaced?
The valve body itself, generally not. The coil, yes, in the sense that it is simply replaced on its own. Which is exactly why establishing which one has failed matters so much before anything is ordered.
They tapped the valve with a wrench and said it is stuck.
We would want a second opinion on that. Trade guidance is explicit that striking a reversing valve can crack the seats or damage the slider, creating an internal leak that was not there. A diagnosis that arrives immediately after somebody hit the part is worth checking.
Let us check the setting and the coil first.
Book online in about a minute. Tell us whether a thermostat was changed recently — it matters more than you would think.
Book a Diagnostic Visit60 seconds online · or call (206) 486-6373
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