Common Furnace Problems in Older San Francisco Homes: Urgency Guide

San Francisco's iconic Victorian and Edwardian homes are beautiful—but their aging heating systems present unique challenges. That radiator that's been making strange noises? The pilot light that keeps going out? The uneven heating across your multi-level home?

This guide covers the most common furnace problems in older SF homes, how urgent each problem is, typical repair costs, and what happens if you delay.

Understanding SF's Older Heating Systems

Most pre-1950s San Francisco homes use one of these heating systems:

Steam or Hot Water Radiators

• Cast iron radiators fed by basement boiler
• Common in Victorian/Edwardian homes
• Requires specialized knowledge to repair

Gravity Wall Heaters

• Individual gas wall units (no central system)
• Popular in converted apartments
• Simple but outdated technology

Gravity Floor Furnaces

• Large floor grate, heat rises naturally
• Common in single-family homes
• Often original to 1920s-1940s homes

Forced Air (if retrofitted)

• Central furnace with ductwork
• Usually added later to older homes
• May have undersized or poorly-designed ducts

Problem #1: No Heat (Complete System Failure)

Symptoms

• Thermostat set correctly but no heat
• Pilot light won't stay lit (gas systems)
• System won't turn on at all
• Cold radiators throughout house

Common Causes in Older SF Homes

For Radiator Systems:

• Failed circulator pump (motor that moves hot water)
• Boiler ignition failure
• Low water pressure in system
• Frozen/broken pipes in unheated basement

For Wall Heaters:

• Failed thermocouple (safety device)
• Clogged pilot orifice
• Broken gas valve
• Venting blockage

For Forced Air:

• Cracked heat exchanger (common in 20+ year systems)
• Failed ignitor or flame sensor
• Tripped circuit breaker
• Thermostat failure

Urgency Level: 🔴 EMERGENCY (24-48 hours)

Why it's urgent:

• San Francisco gets cold (40-50°F nights in winter)
• Risk of frozen pipes in unheated home
• Health risk for elderly/young children
• Water damage if boiler pipes freeze

Typical repair cost:

• Thermocouple replacement: $150-$250
• Circulator pump: $400-$700
• Ignitor replacement: $200-$350
• Heat exchanger: $1,200-$2,500 (often means replacement)

What happens if you wait:

• Frozen pipes can burst → $5,000-$15,000 water damage
• Mold growth in cold, damp SF climate
• Uncomfortable/unsafe living conditions

DIY Quick Checks

Before calling for emergency service:

1. Check thermostat batteries and settings
2. Verify circuit breaker hasn't tripped
3. Check pilot light (if accessible)
4. Ensure gas supply valve is open

Problem #2: Uneven Heating (Some Rooms Cold)

Symptoms

• Front rooms warm, back rooms freezing
• Upper floors too hot, lower floors cold
• One or more radiators stay cold
• Some rooms overheat while others stay chilly

Common Causes in Older SF Homes

Victorian/Edwardian Specific:

• Air trapped in radiator lines (very common)
• Failed zone valve
• Closed radiator valve (previous tenant)
• Radiators never properly balanced
• Addition/remodel created heating imbalance

Forced Air Systems:

• Undersized ductwork (common retrofit issue)
• Leaky ducts in uninsulated basement
• Closed or blocked vents
• Single-zone system in multi-level home

Urgency Level: 🟡 MODERATE (1-2 weeks)

Why it matters:

• Not an emergency but impacts comfort
• Energy waste (overheating some areas)
• May indicate underlying issues
• Gets worse over time

Typical repair cost:

• Radiator bleeding/balancing: $150-$300
• Zone valve replacement: $300-$500
• Duct sealing/repair: $500-$1,500
• Multi-zone retrofit: $2,000-$5,000

What happens if you wait:

• Higher energy bills (system works harder)
• Continued discomfort
• Potential system damage from overwork
• Problem often worsens over time

Problem #3: Strange Noises (Banging, Clanking, Hissing)

Symptoms

Steam Radiator Systems:

• Banging/hammering ("water hammer" from condensate)
• Hissing from radiator valves
• Gurgling in pipes

Forced Air:

• Rumbling at startup
• Squealing/screeching blower motor
• Popping from ductwork

Common Causes

Steam Systems (Very Common in SF):

• Improper pitch on radiator (should tilt toward valve)
• Failed steam trap
• Water trapped in lines
• Oversized boiler for system

Forced Air:

• Dirty/failing blower motor bearings
• Expanding/contracting ductwork (normal but annoying)
• Loose mounting bolts
• Worn belt (older systems)

Urgency Level: 🟡 MODERATE to 🟢 LOW

Loud banging/hammering: 🟡 MODERATE (1-2 weeks)

• Can damage pipes and valves over time
• Indicates system imbalance
• Disruptive to sleep/quality of life

Squealing/grinding: 🟡 MODERATE (1-2 weeks)

• Motor may fail suddenly
• Gets progressively worse
• Indicates worn bearings

Hissing/gurgling: 🟢 LOW (1 month)

• Usually just air in system
• Easy fix (bleeding radiators)
• Not damaging but annoying

Typical repair cost:

• Radiator re-pitching: $150-$300 per unit
• Blower motor replacement: $400-$800
• Steam trap replacement: $200-$400
• Air bleeding: $100-$200

What happens if you wait:

• Motor burnout (if squealing)
• Pipe damage (if hammering)
• Decreased efficiency
• Louder noises over time

Problem #4: Pilot Light Won't Stay Lit

Symptoms

• Pilot lights but goes out immediately
• Won't light at all
• Lights but system won't fire up
• Yellow flame instead of blue

Common Causes in Older SF Homes

Thermocouple failure (most common)

• Safety device that shuts off gas if pilot dies
• Wears out over 5-10 years
• Cheap part, easy fix

Drafty/poor venting

• SF's windy conditions blow out pilot
• Cracked flue pipe
• Bird nest in chimney (common in SF)

Dirty pilot orifice

• Years of dust/debris
• Especially common in basement furnaces

Gas pressure issues

• Low gas pressure from PG&E
• Clogged gas line

Urgency Level: 🟡 MODERATE (3-7 days)

Why it matters:

• No heat until fixed
• Could indicate gas safety issue
• May worsen (complete failure)

Special safety note: If you smell gas, leave immediately and call PG&E + Fire Dept. Don't try to relight.

Typical repair cost:

• Thermocouple replacement: $150-$250
• Pilot orifice cleaning: $100-$200
• Flue pipe repair: $300-$800
• Venting repair: $500-$1,500

What happens if you wait:

• System won't work at all
• Potential gas safety issue
• Cold home in SF winter

Problem #5: Yellow or Flickering Flame

Symptoms

• Flame is yellow/orange instead of blue
• Flame flickers or "dances"
• Soot buildup around burner
• Smell of gas or exhaust

Common Causes

Incomplete combustion:

• Dirty burners (decades of use)
• Insufficient air supply
• Cracked heat exchanger
• Blocked venting

Carbon buildup:

• Never been professionally cleaned
• Poor air quality in basement

Urgency Level: 🔴 HIGH PRIORITY (24-72 hours)

Why it's urgent:

• Carbon monoxide risk (can be deadly)
• Indicates incomplete combustion
• May signal cracked heat exchanger
• Health hazard for household

Immediate action:

• Turn off system
• Open windows
• Install/check CO detectors
• Call HVAC professional immediately

Typical repair cost:

• Professional cleaning: $200-$400
• Heat exchanger replacement: $1,200-$2,500
• Venting repair: $500-$1,500
• Full system replacement: $5,000-$12,000

What happens if you wait:

• Carbon monoxide poisoning risk
• System failure
• Potential fire hazard
• Health risks increase

Problem #6: Cycling On/Off Frequently

Symptoms

• Furnace turns on every 5-10 minutes
• Runs briefly then shuts off
• Never reaches temperature
• House stays slightly cool

Common Causes in Older SF Homes

Dirty air filter (most common, easiest fix)

• Restricts airflow
• System overheats, shuts off for safety
• Replace monthly in dusty SF homes

Thermostat issues:

• Old mercury thermostats lose calibration
• Located in wrong spot (drafty hallway)
• Faulty wiring

Oversized system:

• Replacement furnace too large for home
• Heats quickly then shuts off
• Common retrofit mistake

Flame sensor dirty:

• Buildup from years of use
• Simple cleaning fixes it

Urgency Level: 🟢 LOW to 🟡 MODERATE (1-3 weeks)

Why it matters:

• Wastes energy (inefficient operation)
• Wears out components faster
• Uncomfortable temperature swings
• Higher utility bills

Typical repair cost:

• Air filter replacement: $20-$50 (DIY)
• Flame sensor cleaning: $150-$250
• Thermostat replacement: $150-$400
• None if just filter change!

What happens if you wait:

• Higher PG&E bills
• Premature component failure
• Continued discomfort
• System works harder, ages faster

Problem #7: Musty or Burning Smell

Symptoms

Musty/moldy smell:

• Damp basement smell
• Worse when heat turns on
• Lingering in rooms

Burning smell:

• Dust burning (normal at season start)
• Electrical burning (wiring issue)
• Plastic/rubber burning (serious)

Common Causes in SF Homes

Musty smell:

• Mold/mildew in basement (SF's damp climate)
• Dirty ducts
• Water leak in system
• Condensation issues

Burning smell:

• Season-start dust (normal, goes away in hours)
• Overheating motor
• Electrical short
• Cracked heat exchanger leaking exhaust

Urgency Level: Varies

Dust burning at season start: 🟢 NORMAL

• Should dissipate in 1-2 hours
• Open windows, run system
• No action needed if stops

Musty smell: 🟡 MODERATE (1-2 weeks)

• Indoor air quality issue
• May indicate mold problem
• Not immediately dangerous

Electrical/plastic burning: 🔴 EMERGENCY

• Turn off system immediately
• Potential fire hazard
• Call professional same day

Typical repair cost:

• Duct cleaning: $400-$800
• Mold remediation: $500-$3,000
• Electrical repair: $200-$600
• Blower motor: $400-$800

Problem #8: High Energy Bills

Symptoms

• PG&E bill suddenly higher
• Bill increases without usage change
• Furnace runs constantly
• Never seems to reach temperature

Common Causes in Older Homes

Poor insulation:

• Victorian homes often have zero insulation
• Heat escapes through walls/windows
• Single-pane windows (very common in SF)

Aging, inefficient equipment:

• 80% efficiency (vs. modern 95%+)
• 30+ year old boiler
• Wears out, loses efficiency

Duct leaks (if forced air):

• 20-30% heat loss in basements (common)
• Poor original installation
• Disconnected segments

Thermostat placement:

• Located in coldest room
• Near drafty door
• System overworks trying to heat that one spot

Urgency Level: 🟢 LOW (Address during off-season)

Why it matters:

• Costs money monthly
• Environmental impact
• Indicates underlying issues
• May worsen over time

Typical solutions & costs:

• Duct sealing: $500-$1,500
• Insulation (attic): $1,500-$3,000
• Thermostat relocation: $200-$400
• System upgrade: $5,000-$12,000 (but 30-50% savings)

What happens if you wait:

• Continued high bills
• Wasted energy
• Unnecessary carbon footprint
• Money lost vs. upgrade savings

Urgency Quick Reference Chart

Problem	Urgency	Timeline	Risk if Delayed
No heat	🔴 Emergency	24-48 hrs	Frozen pipes, water damage
Yellow flame	🔴 High	24-72 hrs	Carbon monoxide risk
Burning smell	🔴 Emergency	Immediately	Fire hazard
Pilot won't stay lit	🟡 Moderate	3-7 days	No heat, possible gas issue
Uneven heating	🟡 Moderate	1-2 weeks	Discomfort, higher bills
Strange noises	🟡 Moderate	1-2 weeks	Component damage
Short cycling	🟢 Low	1-3 weeks	Higher bills, wear
High energy bills	🟢 Low	Off-season	Wasted money

San Francisco-Specific Considerations

Why SF Homes Are Different

Microclimate variations:

• Foggy Sunset/Richmond = more heating needs
• Sunny Mission/Potrero = less heating
• Same system performs differently by neighborhood

Victorian/Edwardian construction:

• Zero insulation in walls
• High ceilings (heat rises, rooms stay cold)
• Original systems 80-120 years old
• Additions/renovations created heating challenges

Earthquake retrofitting:

• May have damaged ductwork/pipes
• Foundation work affects basement systems
• Seismic bracing can pinch gas lines

Strict building codes:

• SF requires permits for many repairs
• Historic preservation rules in some neighborhoods
• HOA restrictions in condo buildings

When to Repair vs. Replace

Repair if:

• System less than 15 years old
• Single component failure
• Repair cost <$1,000
• Otherwise functioning well

Replace if:

• System 20+ years old
• Multiple repairs needed
• Repair cost >$2,000
• 80% efficiency or lower
• Frequent breakdowns

Break-even calculation: New high-efficiency system typically pays for itself in 8-12 years through energy savings.

What Galaxy Heating & Air Conditioning Offers

Emergency Service:

• Same-day service for urgent issues
• 24/7 availability
• All SF neighborhoods

Victorian/Edwardian Expertise:

• Steam radiator specialists
• Boiler repair & replacement
• Understanding of historic systems

Honest Diagnostics:

• We'll tell you repair vs. replace truth
• Transparent pricing
• Written estimates

Permit Handling:

• We pull all required SF permits
• Navigate historic preservation rules
• Handle HOA approvals

Bottom Line: When to Act

Call immediately (same day):

• No heat in cold weather
• Gas smell
• Yellow flame
• Burning smell (not dust)
• Loud banging/grinding

Schedule within a week:

• Pilot light issues
• Uneven heating
• Strange noises
• Short cycling

Address during off-season:

• High energy bills
• Minor efficiency issues
• Preventive upgrades

Don't delay if:

• You have elderly/young family members
• Temperatures dropping below 50°F
• Any safety concerns
• Problem getting worse

Need Furnace Repair in San Francisco?

Galaxy Heating & Air Conditioning specializes in older SF homes. Our technicians understand Victorian radiator systems, gravity heaters, and the unique challenges of heating San Francisco's historic housing stock.

Same-day emergency service available.

Schedule Furnace Repair | Call (925) 578-3293

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Remember: That strange noise or smell might seem minor, but it could indicate a serious problem. When in doubt, get it checked—a $150 service call can prevent a $5,000 emergency repair.