You switched to a heat pump — new install, a changeout, or it came with the house — and now it seems to run all the time. Then the electric bill arrives, far higher than expected, and the obvious conclusion is that the constant running is burning money.
Sometimes that's true. Often it isn't. A heat pump is a fundamentally different machine from a gas furnace, and long runtimes are part of the design. But there is one fault that produces exactly this symptom and genuinely does cost a fortune.
How it usually shows up:
- The system runs nearly continuously on cold mornings and evenings.
- The electric bill jumped sharply versus last year or versus the gas furnace it replaced.
- "AUX" or "AUX HEAT" appears on the thermostat, sometimes for long stretches.
- The house is comfortable, but the runtime and the bill feel wrong.
First, the normal behavior
Heat pumps are designed to run long, low-output cycles. A gas furnace fires at full output, blasts the house to temperature, and shuts off. A heat pump produces gentler heat continuously, holding the house steady rather than sprinting — and that steady low-output operation is how it achieves its efficiency. The vent air also feels cooler than a furnace's (around 85–110°F versus 120–140°F), which adds to the impression that it's struggling when it isn't.
So a heat pump that runs for hours on a cold morning while the house sits at the set point is very likely working correctly. What is not normal: never reaching the set point, runtime clearly worse than last winter, or a bill that spiked without a cold snap.
The expensive one: auxiliary heat stuck on
Nearly every heat pump has backup heat, usually electric resistance strips in the air handler, for the coldest days and during defrost. That backup is several times more expensive to run than the heat pump itself, because resistance heat converts electricity to heat one-for-one while a heat pump moves several units of heat per unit of electricity. If those strips run when they shouldn't, your bill doesn't creep up — it jumps.
Check your thermostat right now. If it's set to EM HEAT or EMERGENCY HEAT, that's the whole problem: that mode locks out the heat pump and runs the expensive strips full time. Set it back to HEAT. People land in EM HEAT by accident constantly.
If the thermostat is correctly on HEAT but "AUX" still shows for long stretches in mild weather, something is calling for backup when it shouldn't: a miswired or mis-configured thermostat, a wrong balance-point setting, a failed outdoor sensor, or a heat pump that has lost capacity.
Other real faults behind constant running
- Low refrigerant from a leak. Lost capacity means the heat pump can't keep up, so it runs continuously and leans on aux heat. Low charge always means a leak. Licensed-tech only (EPA 608).
- A dirty filter or coil. Restricted airflow cuts capacity and extends runtime — the cheapest and most common contributing cause.
- An iced-over outdoor unit. A coil encased in ice can't absorb heat from outdoor air, so the system runs endlessly and falls back on the strips.
- A failed defrost control board or sensor. When defrost doesn't work, the outdoor coil ices up and never clears.
- Leaky ducts. Ductwork in a cold attic or crawlspace means the heat pump is heating spaces you don't live in.
- An undersized system. A unit too small for the house runs continuously by definition and calls aux heat regularly.
- Aggressive thermostat programming. Dropping the house 8° overnight and asking for it all back at 6 a.m. creates a recovery demand the heat pump can't meet alone, so the thermostat brings in the expensive strips to catch up. Steady setpoints, or shallow 2–3° setbacks with adaptive recovery, cost less.
The usual fix
Our tech starts by confirming what's actually running — heat pump alone, or heat pump plus strips — and when. That single measurement separates a normal long-cycling heat pump from a bill-eating aux-heat problem. From there we check thermostat configuration and wiring (mode, staging, balance point), verify airflow, read refrigerant charge, and test the defrost board and sensor if the outdoor unit has been icing. If it comes down to duct leakage or an undersized system, we'll say so plainly rather than replace parts that won't change your bill.
DIY vs. calling a pro — the honest version
Safe to check yourself first (free):
- Confirm the thermostat is set to HEAT, not EM HEAT. The highest-value check on this page.
- Change the air filter if it's dirty, and make sure registers and return grilles aren't blocked.
- Clear the outdoor unit of leaves and debris and keep a couple of feet of clearance. If it's iced solid, turn the system off and let it thaw — never chip at the ice.
- Switch to steady setpoints. Pick a temperature and leave it, or use no more than a 2–3° setback.
- Compare your bill to the weather. A cold snap explains a higher bill; a jump during mild weeks does not.
Call a pro when:
- "AUX" shows for long stretches in mild weather with the thermostat correctly on HEAT.
- The house doesn't reach the set point despite running constantly.
- The outdoor unit ices over or freezes again right after thawing.
- Runtime or bills are clearly worse than last winter with a clean filter installed.
- You suspect low refrigerant, a defrost fault, or thermostat miswiring.
Refrigerant, defrost controls, and heat-strip circuits carry high pressure and line voltage — a licensed tech pays for itself here.
What it costs in the Bay Area
Heat-pump repairs vary widely by the part. In our pricing, a defrost control board runs about $180–$500 — a common fix when icing drives constant running and aux heat. A refrigerant leak repair plus recharge is roughly $180–$700 depending on the leak, and a reversing valve is the high end at $450–$900. Thermostat configuration and wiring corrections are among the cheapest things we do, and often what actually fixes your bill. We charge a diagnostic fee that's credited toward the repair when you approve the work, and you'll always see a flat, upfront price before we start — no surprise line items.
Get your runtime and your bill back under control
Triton repairs heat pumps, central AC, and mini-splits across the Tri-Valley, East Bay, and Peninsula — Dublin, Pleasanton, Livermore, San Ramon, and Hayward, where heat pumps are increasingly the default install. Same-week (often same-day) appointments and licensed techs.
Book online or call (888) 993-5699. We'll find out whether your heat pump is working as designed or quietly running on resistance heat.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- Heat Pump Not Heating / Blowing Cold Air — when it truly won't heat
- Heat Pump Frozen / Iced-Over Outdoor Unit — when the coil ices solid
- HVAC Repair or Replace? — how we run the numbers
- HVAC & Heat Pump Repair in Dublin — Tri-Valley service area
Frequently asked questions
Is it normal for a heat pump to run constantly? Often, yes. Heat pumps are designed for long, low-output cycles rather than the short bursts of a gas furnace, so running for hours while holding the set point is normal in cold weather. It's a problem when the house never reaches the set point, runtime is clearly worse than last winter, or the bill jumps without a cold snap.
Why is my electric bill so high with a heat pump? The usual culprit is auxiliary or emergency heat — electric resistance strips that convert electricity to heat one-for-one, while the heat pump moves several units of heat per unit of electricity. Check that your thermostat says HEAT and not EM HEAT, and watch whether AUX shows in mild weather.
Should I use a big overnight setback with a heat pump? No. Recovering 8 degrees in the morning is more than the heat pump can do alone, so the thermostat brings in costly backup heat and you lose more than you saved. Steady setpoints, or a shallow 2 to 3 degree setback with adaptive recovery, cost less.
Why does my heat pump run nonstop and still not warm the house? That points to lost capacity rather than normal long cycling — low refrigerant from a leak, a dirty filter or coil, an iced-over outdoor unit, a failed defrost board, leaky ducts, or an undersized system. It needs a tech to measure airflow and refrigerant charge.
How much does it cost to fix a heat pump that runs constantly in the Bay Area? It depends on the cause: a defrost control board is about $180–$500, a refrigerant leak repair and recharge runs roughly $180–$700, and a reversing valve is the high end at $450–$900. Thermostat corrections are usually much cheaper and are often the actual fix. We credit the diagnostic fee toward the repair and give you a firm price before any work begins.