Furnace Running But Not Heating? Heat Pump Blowing Cold Air? Common HVAC Problems & Fixes

Furnace Running But Not Heating? Heat Pump Blowing Cold Air? Here's What to Do

Your thermostat says 68°F, but your house feels like 60°F. The furnace is running—you can hear it—but no heat is coming out.

Or maybe your heat pump is blowing air, but it feels cool instead of warm.

Before you panic and call for emergency service (potentially paying $200-400 for an after-hours call), let's troubleshoot. Many "no heat" problems have simple fixes you can do yourself in 5 minutes.

We'll cover what you can fix, what needs a professional, and when to call for emergency service RIGHT NOW. (If your system is older and you're facing repeated repairs, check out our repair vs. replace guide to see if replacement makes more sense.)

Quick Diagnostic: Start Here

Before we dive into specific problems, answer these questions:

1. Is the system actually running?

• Can you hear the blower motor?
• Is air coming out of vents (even if not warm)?
• Is the outdoor unit running (for heat pumps)?

2. What does the thermostat say?

• Is it set to "HEAT" (not "COOL" or "OFF")?
• Is it set to "AUTO" (not "FAN ONLY")?
• Is the target temperature higher than current room temperature?
• Does it have batteries? Are they fresh?

3. When did the problem start?

• First cold day of the season? (Different troubleshooting)
• After a power outage? (Likely reset issue)
• Gradually over time? (Maintenance issue)
• Suddenly overnight? (Component failure)

Your answers determine where to start troubleshooting.

Problem #1: Furnace Running But No Heat

Symptoms:

• Blower motor running (you hear it)
• Air coming from vents
• Air is room temperature or slightly warm (not hot)
• Thermostat shows lower temp than set point

Fix #1: Check Your Air Filter (80% of "No Heat" Calls)

Why this matters: A clogged air filter is the #1 cause of heating problems. When the filter is dirty:

• Airflow is restricted
• Furnace overheats and shuts down for safety
• No heat reaches your home
• System runs constantly trying to reach temperature

How to check:

1. Locate your filter (usually at return air grille or in furnace cabinet)
2. Pull it out
3. Hold it up to light—if you can't see through it, it's clogged

What to do:

• Replace disposable filters immediately ($5-20)
• Clean reusable filters per manufacturer instructions
• Set reminder to check monthly

Bay Area note: Wildfire season (June-November) clogs filters faster. Check weekly during smoke events.

Expected result: Heat should return within 5-10 minutes of replacing filter.

Fix #2: Check Thermostat Settings

Common mistakes:

• Set to "FAN ONLY" instead of "HEAT"
• Fan set to "ON" instead of "AUTO"
• Temperature set below current room temp
• Heat/Cool mode switch in wrong position

How to fix:

1. Set mode to "HEAT" (not AUTO, COOL, or OFF)
2. Set fan to "AUTO" (not ON)
3. Raise temperature 5°F above current room temp
4. Wait 5 minutes

Smart thermostat troubleshooting:

• Check WiFi connection (system may be offline)
• Verify schedule settings haven't changed
• Replace batteries (even hardwired thermostats have backup batteries)
• Restart thermostat (remove from wall plate for 30 seconds)

Expected result: Furnace should start heating within 3-5 minutes.

Fix #3: Check Circuit Breaker

Why this happens:

• Power surge during startup
• Overload from dirty filter
• Electrical issue
• Breaker wearing out

How to check:

1. Go to your electrical panel
2. Look for tripped breaker (handle in middle position, not full ON or OFF)
3. Furnaces typically use 15-30 amp breaker labeled "FURNACE" or "HVAC"
4. Some systems have a second breaker for AC unit

How to fix:

1. Turn breaker fully OFF
2. Wait 30 seconds
3. Turn fully ON
4. Return to thermostat and wait 5 minutes

Warning: If breaker trips again immediately, DO NOT keep resetting. This indicates an electrical problem requiring professional repair.

Expected result: System should power on and begin heating.

Fix #4: Check Furnace Power Switch

The most embarrassing fix:

Many furnaces have a light switch-style power switch near the unit. It's often mistaken for a regular light switch and accidentally turned off.

Where to look:

• On wall next to furnace
• On furnace cabinet itself
• At top of basement stairs
• Often has red or orange cover plate

How to fix: Simply flip it to ON position.

Expected result: System powers on immediately.

When to Call a Professional: Furnace Issues

Call for service if you've tried the above and still have no heat, OR if you notice:

🚨 Call Emergency Service (Do Not Wait):

• Gas smell (evacuate, call 911, then gas company)
• Carbon monoxide detector alarm (evacuate immediately)
• Burning electrical smell (shut off breaker, call emergency)
• Yellow or orange flames (should be blue—carbon monoxide risk)
• Water leaking around furnace
• Loud bang or explosion sound when furnace starts

📞 Call During Business Hours:

• Pilot light won't stay lit (older furnaces)
• Furnace cycles on/off rapidly (short-cycling)
• Weak or no airflow despite clean filter
• Strange noises (grinding, squealing, banging)
• Error codes on digital display
• Heat works intermittently

Problem #2: Heat Pump Blowing Cold Air in Heat Mode

First, understand this: Heat pump air feels cooler than furnace air.

Furnace air temperature: 120-140°F
Heat pump air temperature: 85-100°F
Your body temperature: 98.6°F

Result: Heat pump air can feel "cool" to your hand even when it's working perfectly. This is NORMAL.

How to tell if it's actually a problem:

• Room temperature is NOT rising over 30+ minutes
• Air feels genuinely cold (same as outdoor temperature)
• Outdoor unit is frozen solid with ice
• System runs constantly but house stays cold

Fix #1: Give Defrost Mode Time

What's happening: Heat pumps occasionally reverse to cooling mode to melt ice buildup on outdoor coils. This is normal and automatic.

During defrost mode:

• Indoor air feels cool (or blows no air)
• Outdoor unit steams or drips water
• Lasts 5-15 minutes
• Happens more frequently in wet/cold weather

Bay Area consideration: Oakland/coastal areas with fog experience more defrost cycles than inland areas.

What to do: Wait 15-20 minutes. If heat returns, this was normal defrost. If system stays in defrost or defrosts constantly, call for service.

Fix #2: Check Outdoor Unit

Common Bay Area problems:

• Leaves, pine needles, or debris blocking airflow
• Cottonwood or tree debris clogging coils
• Ice buildup from sprinkler overspray
• Landscaping grown too close (less than 2 feet clearance)

How to check:

1. Go outside to heat pump unit
2. Look for debris on or around unit
3. Check for ice buildup
4. Ensure plants are 2+ feet away

How to fix:

• Clear visible debris carefully
• Turn off sprinklers near unit
• Trim vegetation
• If ice-covered, call for service (don't chip ice yourself)

Expected result: Heating improves within 15-20 minutes if debris was blocking airflow.

Fix #3: Verify Thermostat Setting

Heat pump-specific settings:

• Some thermostats have "EMERGENCY HEAT" or "AUX HEAT" setting
• Accidentally switching to emergency heat activates backup (expensive electric resistance heat)
• Make sure set to "HEAT" not "EM HEAT"

How to check:

1. Look at thermostat display
2. Should say "HEAT" or "HEATING"
3. Should NOT say "EM HEAT" or "AUX HEAT" (unless outdoor temp is below 25°F)

Expected result: System should switch to normal heat pump operation.

When to Call a Professional: Heat Pump Issues

🚨 Call Emergency Service:

• Outdoor unit completely frozen in ice
• Electrical burning smell
• Loud grinding or screeching from outdoor unit
• No heat and outdoor temp below 50°F (comfort emergency)
• Water leaking inside home near air handler

📞 Call During Business Hours:

• Frequent defrost cycles (every 15-30 minutes)
• Cool air persists after 30+ minutes
• Ice accumulation on outdoor unit even in dry weather
• Hissing or bubbling sounds (refrigerant leak)
• Outdoor fan not spinning when system runs
• Strange odors from vents

Problem #3: Weak Airflow or Uneven Heating

Symptoms:

• Some rooms hot, others cold
• Weak air coming from vents
• System runs constantly
• High energy bills

Fix #1: Check All Vents

Common issues:

• Furniture blocking return or supply vents
• Vents closed or partially closed
• Curtains covering vents
• Rugs blocking floor registers

Bay Area homes: Victorian and older homes often have poor duct design with long runs to some rooms.

How to fix:

1. Walk through home checking every vent
2. Move furniture away from vents (6+ inches)
3. Open all vents fully
4. Remove obstructions

Expected result: Improved airflow and more even temperatures.

Fix #2: Ductwork Issues (Requires Professional)

Common Bay Area duct problems:

• Ducts in unconditioned attic (huge energy waste)
• Disconnected ducts
• Crushed or kinked flexible ducts
• Gaps at joints (30%+ air leakage typical)
• Undersized ducts for modern equipment

Signs you have duct problems:

• Huge temperature differences between rooms
• Dusty home despite cleaning
• High energy bills
• Attic is hot in summer, cold in winter
• Visible gaps or disconnections in accessible ductwork

What to do: Schedule professional duct inspection and sealing. Many Bay Area utility companies offer rebates for duct sealing ($500-1,500).

Problem #4: System Cycles On and Off Repeatedly

Symptoms:

• Furnace or heat pump starts, runs 2-5 minutes, shuts off
• Repeats every 5-10 minutes
• Never reaches set temperature
• Higher energy bills

Common causes:

• Dirty filter (restricts airflow, system overheats)
• Thermostat in wrong location (near heat source, draft, or sunlight)
• Oversized equipment (reaches temp too fast, shuts off)
• Flame sensor dirty (furnaces)
• Defrost cycle problems (heat pumps)

DIY Fixes:

1. Replace filter (even if recently changed—wildfire smoke clogs fast)

2. Check thermostat location:

• Should be on interior wall
• 5+ feet from windows
• Away from heat sources (lamps, appliances, sunlight)
• Away from drafts (doors, windows, vents)

3. Verify no phantom heat sources:

• Space heaters near thermostat
• Sunlight hitting thermostat
• Lamps or electronics near thermostat

Professional Fixes:

Requires HVAC technician:

• Flame sensor cleaning (furnaces)
• Limit switch adjustment
• Refrigerant charge (heat pumps)
• Defrost control board (heat pumps)
• System downsizing if oversized

Bay Area-Specific Heating Problems

Coastal Areas (Oakland, SF, Berkeley, Alameda)

Unique challenges:

• Salt air corrosion (heat pump coils deteriorate faster)
• Fog/moisture (more defrost cycles, mold in ducts)
• Mild temps mean minimal heating (systems get "rusty" from non-use)

Solutions:

• Annual professional cleaning critical
• Coastal-rated equipment if replacing
• Run system briefly monthly year-round (prevents seized components)

Inland Areas (Walnut Creek, Concord, Pleasanton)

Unique challenges:

• Temperature swings (cold mornings, warm afternoons confuse thermostats)
• Dry air (ducts leak more, static electricity issues)
• Debris (leaves, cottonwood, dust clog outdoor units faster)

Solutions:

• Programmable thermostats handle swings better
• Regular outdoor unit cleaning
• Duct sealing to prevent leakage

Older Bay Area Homes (Pre-1980)

Common problems:

• Undersized ducts (can't handle modern high-efficiency equipment)
• No return air in some rooms
• Knob-and-tube wiring (insufficient for modern HVAC)
• Minimal insulation (system works harder)

Solutions:

• Duct modifications during replacement
• Ductless mini-splits for problem rooms
• Insulation upgrades
• Electrical panel upgrades if needed

When to Call Galaxy Heating & Air Conditioning

We Can Fix Over the Phone:

Sometimes a quick diagnostic call solves the problem:

• Thermostat setting questions
• Filter type/size guidance
• Circuit breaker reset procedures
• Defrost mode explanation

Call (925) 578-3293 for free phone troubleshooting.

Schedule Service Call For:

Same-Day Service Available:

• No heat and outdoor temp below 55°F
• Intermittent heating
• Strange noises or smells
• Error codes displayed
• Recent power outage caused issues

Next-Day Service:

• Weak airflow
• Some rooms not heating
• System cycling frequently
• Annual maintenance due
• Want professional inspection before winter

Emergency Service (24/7) For:

• Gas smell (call 911 first, then us)
• Carbon monoxide alarm
• Electrical burning smell
• Water leaking
• No heat with vulnerable household members (elderly, infants)
• Outdoor temperature below 40°F with no heat

Prevention: Avoid "No Heat" Emergencies

Monthly (5 minutes):

• Check air filter
• Listen for unusual noises
• Verify even heating throughout home
• Test thermostat

Annually (Schedule Professional):

• Complete HVAC maintenance tune-up ($150-200)
• Cleaning and inspection
• Catch small problems before failure
• Maintain manufacturer warranty

Bay Area Timing:

• Schedule maintenance in October (before heating season)
• Second service in March (before cooling season for heat pumps)

What's included in tune-up:

• Clean burners and heat exchanger (furnaces)
• Clean coils (heat pumps)
• Check refrigerant charge (heat pumps)
• Test safety controls
• Measure temperature split
• Inspect electrical connections
• Lubricate moving parts
• Check ductwork for leaks

ROI of maintenance:

• Prevents 95% of breakdowns
• Extends equipment life 3-5 years
• Maintains efficiency (saves $100-300/year)
• Catches safety issues early
• Maintains warranty coverage

The Bottom Line

Try these first (5-10 minutes):

1. ✅ Replace air filter
2. ✅ Check thermostat settings
3. ✅ Reset circuit breaker
4. ✅ Check furnace power switch
5. ✅ Clear outdoor unit debris (heat pumps)

Call for professional help if:

• ❌ DIY fixes don't work within 30 minutes
• ❌ You smell gas or burning
• ❌ You see error codes
• ❌ System is making strange noises
• ❌ It's your first time dealing with HVAC

Call emergency service immediately if:

• 🚨 Gas smell
• 🚨 Carbon monoxide alarm
• 🚨 Electrical burning smell
• 🚨 Yellow/orange flames
• 🚨 Water leaking

Ready to Get Your Heat Working?

Free phone troubleshooting: (925) 578-3293

Online scheduling: Schedule service

What to expect:

• NATE-certified technicians
• Diagnostic fee waived with repair
• Upfront pricing (no surprise charges)
• Same-day service available
• 5-year labor warranty on repairs
• 24/7 emergency service

Serving: Walnut Creek, Concord, Pleasant Hill, Lafayette, Orinda, Moraga, Danville, Alamo, Oakland, Berkeley, Alameda, and throughout the Bay Area.

We're honest: If it's a simple fix you can do yourself, we'll walk you through it over the phone. If you need professional service, we'll be there fast.

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Galaxy Heating & Air Conditioning | CSLB License #1076868 (C-20 HVAC, C-10 Electrical, B General Building)