Your wall or floor furnace won't light, or the pilot lights but the burner never comes on and the house stays cold. In a lot of Bay Area homes this is an especially common call, because so many of our older houses — across the Peninsula and the older East Bay — still heat with gravity wall and floor furnaces rather than a central system. These units are a genuine Bay Area staple, and they have their own quirks and failure points that a modern furnace doesn't.
This page walks through what actually keeps a wall or floor furnace from heating, what you can safely check yourself, and when it's time for a licensed tech — with extra attention to gas safety, because these are older gas appliances.
How it usually shows up:
- The pilot won't light at all, or it lights and goes right back out when you release the knob.
- The pilot stays lit but the main burner never kicks on, so there's no real heat.
- The furnace lights but the flame is weak, yellow, or sooty instead of a clean blue.
- On a fan-equipped model, the burner runs but little or no warm air moves through the grille.
Why your wall or floor furnace won't heat
Most no-heat calls on these units come down to one of these:
- A bad thermocouple (pilot won't stay lit). This is the single most common failure on a standing-pilot unit. The thermocouple senses the pilot flame and tells the gas valve it's safe to stay open; when it weakens, the valve shuts the gas off the moment you let go of the knob.
- A dirty pilot orifice. Dust and lint clog the tiny pilot opening, so the flame is small and can't properly heat the thermocouple. Common in old floor furnaces that draw air up from a dusty crawlspace.
- A failing gas valve. If the valve itself fails, the pilot may light but the main burner never gets gas — or nothing lights at all.
- Dirty burners. Years of dust, rust, and debris block the burner ports, giving a weak, uneven, or yellow flame instead of clean blue heat.
- Thermostat or the old knob control. A dead thermostat battery, a wiring fault, or a worn original knob-style control can stop the furnace from ever calling for heat.
- A failed blower (fan models). Some wall furnaces use a fan to push warm air into the room. If that blower motor fails, the burner may fire but little heat actually reaches you.
The usual fix
Our tech starts at the pilot and the safety circuit, since that's where most of these units fail. From there it's usually one of a few paths: replace a weak thermocouple, clean or replace a clogged pilot assembly and orifice, clean the burners for a clean flame, replace a failing gas valve, or on fan models replace a dead blower. Every gas job includes a safety check of the flame and venting. You get a firm quote before any part goes in.
Gas safety comes first
These are older gas appliances, and gravity furnaces vent by natural draft, so a few safety rules matter more here than almost anywhere else in the home:
- If you smell gas (a rotten-egg odor), don't flip switches or hunt for the source — leave the house and call your gas utility or 911 from outside.
- Carbon monoxide is the real danger with any aging gas furnace. A cracked heat exchanger or bad venting can send CO into the living space. Keep working CO detectors nearby, and if the flame burns yellow and sooty, shut the furnace off and call a tech.
- Never bypass a safety. The thermocouple and gas valve exist to shut the gas off when something is wrong — a unit that won't stay lit is often just doing its job.
DIY vs. calling a pro — the honest version
Safe to check yourself first (free):
- Relight the pilot following the instructions printed on the unit's data plate — most wall and floor furnaces spell out the exact steps right on the door.
- Confirm the gas is on at the shutoff valve, and check that other gas appliances in the house are working.
- Replace the thermostat batteries and make sure it's set to HEAT, above room temperature.
- Change or clean the filter if your model has one, and keep the grille clear of rugs and furniture.
Call a pro when:
- The pilot won't stay lit after relighting — that's usually a thermocouple.
- You smell gas at any point, or the flame is yellow and sooty.
- The pilot is fine but the main burner won't fire (often the gas valve).
- You suspect a cracked heat exchanger or any venting problem.
Gas valves, thermocouples, and heat exchangers involve live gas and combustion — this is where a licensed tech pays for itself and keeps everyone safe.
What it costs in the Bay Area
Wall and floor furnace repairs vary by the part. In our pricing, a thermocouple runs about $80–$280 and a pilot assembly $100–$320 — the common, inexpensive fixes. A gas valve is roughly $150–$450, and on fan models a blower is about $180–$500. 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 wall or floor furnace working again
Triton services gravity wall and floor furnaces along with central heating across the Peninsula and East Bay — San Mateo, Burlingame, Redwood City, Alameda, San Leandro, and Hayward, where so many of the older homes still run on these units. Same-week (often same-day) appointments, upfront pricing, and licensed techs who actually know these older systems.
Book online or call (888) 993-5699. We'll get a tech out to find the fault and get heat back — safely.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- Pilot Light Won't Stay Lit — the thermocouple fix in depth
- Furnace Not Heating / No Heat — central furnace diagnosis
- HVAC & Furnace Repair in Alameda — East Bay service area
Frequently asked questions
Why won't my wall furnace pilot stay lit? The usual cause is a worn thermocouple — the safety sensor that keeps the gas valve open only while it senses the pilot flame. When it weakens, the valve shuts the gas off the instant you release the knob. A dirty pilot orifice that gives a small flame does the same thing. Both are routine repairs for a tech.
Why is my floor furnace pilot lit but the burner won't fire? If the pilot burns but the main burner never lights, the problem is usually downstream of the pilot: a failing gas valve, a thermostat or old knob control that isn't calling for heat, or on fan models a dead blower. It needs a tech to test the valve and controls.
Are old gravity wall and floor furnaces safe? A well-maintained unit that burns a clean blue flame and vents properly is generally safe, but aging gas furnaces carry a real carbon monoxide risk from cracked heat exchangers or bad venting. Keep working CO detectors, watch for a yellow sooty flame, and have the unit checked if anything seems off.
What should I do if I smell gas? Leave the house right away without flipping any switches or lighting anything, then call your gas utility or 911 from outside. Don't try to find the leak yourself. Only go back inside once the utility says it's safe.
Can I replace a thermocouple myself? It's a common part, but on an older gravity furnace we don't recommend DIY gas work — a poor connection can leak gas or defeat the safety shutoff. A tech replaces it, confirms the pilot and flame, and safety-checks the valve and venting at the same time.
How much does wall or floor furnace repair cost in the Bay Area? It depends on the part: a thermocouple is about $80–$280 and a pilot assembly $100–$320, a gas valve runs roughly $150–$450, and on fan models a blower is about $180–$500. We credit the diagnostic fee toward the repair and give you a firm price before any work begins.