The thermostat says 72. The room says 61. The screen even shows the little "heating" indicator. And the house is completely silent — no blower, no hum from the outdoor unit, nothing.
This is one of the most common calls we take between October and March, and the good news is that a real share of them never needed a technician. The thermostat is a switch, not the machine. When it says the system is on, all it's really telling you is that it thinks it sent a signal. Whether that signal arrived, and whether the equipment could do anything with it, are two separate questions.
Here's the order we work through it, starting with everything that costs you nothing.
First, understand what "on" means on the display
Your thermostat runs on 24 volts, usually supplied by a small transformer inside the indoor air handler or furnace. Many models also carry AA batteries as a backup. That means the screen can be bright, responsive, and showing a heat call while the outdoor unit's 240-volt circuit is stone dead.
A working display proves one thing: the thermostat has power. It proves nothing about the heat pump. Keep that in mind as you go down this list, because it's the single most common source of confusion on these calls.
If you'd rather skip straight to a diagnosis, heat pump repair is what we do all week, Monday through Friday, 8 to 6, with same-week scheduling in most of King, Pierce, and Thurston counties.
The free checks, in the order a tech does them
1. Mode, setpoint, and the fan switch
Sounds insulting. Isn't. Confirm the mode is set to HEAT (or COOL) and not OFF, AUTO, or EM HEAT. Then push the setpoint at least three degrees past the current room temperature — a one-degree gap often sits inside the thermostat's deadband and won't trigger anything.
Set the fan to AUTO. If the fan is set to ON and you hear air moving but the house isn't warming, that's a different problem entirely and points at the equipment, not the signal.
2. Wait five to ten minutes
Every modern heat pump has a compressor time delay, usually three to five minutes, to protect the compressor from restarting against high head pressure. Some smart thermostats stack their own delay on top. A lot of "nothing happens" turns into "oh, there it goes" at minute four.
3. Both breakers
A heat pump system has at least two circuits: one for the outdoor unit (a 30 to 40 amp 240V double-pole breaker) and one for the indoor air handler or furnace. Check both. A tripped breaker doesn't always look obviously tripped — the handle can sit in a mushy middle position. Push it firmly to OFF, then back to ON.
If it trips again immediately, stop. That's a short or a locked compressor, and resetting it repeatedly can turn a cheap repair into an expensive one.
4. The outdoor disconnect
There's a small gray box on the wall near the outdoor unit with a pull-out handle or a switch inside. Landscapers, painters, roofers, and previous technicians all have reasons to shut it off. We've driven to more than a few of these.
5. Thermostat batteries and the furnace door switch
Weak batteries can leave the screen lit while the relay can't hold a call. Swap them. Then check the indoor unit's access panel — most air handlers and furnaces have a door safety switch that kills everything if the panel isn't seated. If someone recently changed a filter, that's your candidate.
6. The filter and the condensate float switch
A badly clogged filter can trip a high-limit or freeze the coil and lock the system out. And nearly every indoor coil sits over a drain pan with a float switch wired into the 24-volt circuit. When the drain line plugs — extremely common in our damp climate — that switch opens and shuts the system down on purpose to keep water off your floor. The thermostat has no idea. It just keeps displaying the call.
When the thermostat itself is the problem
Sometimes the switch really is broken. The usual suspects:
- A loose or corroded wire at the terminal block. Two decades of thermal cycling loosens screws. A single backed-out wire on the O/B, Y, or W terminal will produce exactly this symptom.
- A missing C-wire. Smart thermostats need continuous 24V power. Installed without a common wire, they "power-steal" through the heat call and can behave erratically, especially in cold weather.
- Wrong configuration. Heat pumps need the thermostat configured for a heat pump, with the reversing valve set correctly for your brand. A thermostat set up as a conventional furnace will show a heat call and command nothing useful. We wrote more about that in our guide to why a heat pump isn't heating.
- A genuinely dead thermostat. They fail. Rarely, but they do.
When it's the equipment
If the free checks pass and the thermostat is wired and configured correctly, the fault is downstream. In rough order of how often we find it:
Blown low-voltage fuse
There's usually a small 3 or 5 amp automotive-style fuse on the indoor control board. A nicked thermostat wire or a shorted contactor pops it, and the whole 24-volt system goes dark. Cheap part. The real work is finding why it blew.
Failed contactor
The contactor is the relay in the outdoor unit that closes to send 240V to the compressor and fan. Contacts pit and burn, or an ant nest welds them. When it won't pull in, the outdoor unit does absolutely nothing while the indoor blower may still run.
Failed capacitor
The classic. A dead run capacitor means the compressor and fan motor get power but can't start. You'll sometimes hear a hum or a click, then silence. Common, quick, and one of the least expensive repairs on the list.
Control board or defrost board
Boards fail, usually from heat, moisture, or a power surge. Puget Sound winter storms take out their share.
Compressor or motor failure
The expensive end. A seized compressor typically trips the breaker or hums and shuts off on internal overload. On an older system this is where the conversation shifts from repair to replacement.
What this costs
| Situation | Typical cost |
|---|---|
| SituationFree checks that fix it | Typical cost$0 |
| SituationDiagnostic visit | Typical costQuoted before work starts |
| SituationFuse, contactor, capacitor | Typical costLower end of $150 – $1,500 |
| SituationControl board, motor, refrigerant work | Typical costUpper end of $150 – $1,500 |
| SituationCompressor failure on an older unit | Typical costUsually a replacement conversation |
| SituationHeat pump replacement, standard markets | Typical cost$10,000 – $16,000 |
Premium markets run $200 to $2,000 on repairs. You get the number before we touch anything — no diagnosis-then-surprise. Want a ballpark on replacement before anyone visits? The instant estimate tool gives you Good, Better, and Best starting prices in about a minute, and our Washington heat pump cost guide breaks down what drives the range.
Repair or replace, honestly
Under 10 years old and the repair costs less than half a new system? Repair it. That's not a close call.
Past 12 to 15 years, with a four-figure quote, or running R-22 refrigerant that's expensive and getting worse? Put the repair number next to a replacement number before you spend. A new system carries our 10-year parts and labor warranty, and qualifying heat pump installations can earn local utility rebate money when they replace an existing electric or fossil-fuel system — the amount depends on what you're replacing and what you install. Programs change, so we confirm what your utility actually pays and handle the paperwork. Note that rebate programs pay only through their own contractor networks under rules that shift, so we check the current requirements before quoting rather than after. Also worth knowing: rebate eligibility follows the utility that bills your electricity, not your county, so we check your address rather than assume.
And if the honest answer is "this is a $200 capacitor, keep the system," that's what you'll hear. We'd rather fix it than sell you something.
Do this right now
- Push the setpoint three degrees past room temperature and wait ten minutes.
- Check both breakers and the outdoor disconnect.
- Replace the thermostat batteries and confirm the indoor access panel is latched.
- Pull the filter. If it's filthy, replace it.
- Look for water around the indoor unit — that's your float switch.
- If the house is getting cold and your system has emergency heat, switch to EM HEAT to stay warm while you wait. It costs more to run, so switch back after the repair.
Still nothing? That's a service call, not a project. Call (253) 785-4622 or request a visit online and we'll get you on the schedule. Owner-operated, based in Federal Way, and the same people answer the phone after the check clears.