The short answer
Furnace repairs in San Marino usually come down to a specific component: igniter, flame sensor, inducer, pressure switch, control board or blower. SummitAir tests each part in sequence, checks venting and gas safety, and repairs the failed component.
Furnaces in San Marino homes tend to be hidden away: in an attic over a second floor, in a basement or crawl space, behind a closet door in a hallway, or in a detached garage. Some homes have two or more, one serving each floor. When one stops producing heat, the first job is simply figuring out which unit is responsible and getting safe access to it. SummitAir HVAC Contractors is located about two miles northwest in Pasadena and repairs gas furnaces throughout ZIP 91108. On this page we focus on the parts of a furnace that most often fail, explained one component at a time, so you can understand what our technician is looking at.
The ignition system
Most modern furnaces use a hot surface igniter, a small element that glows bright orange to light the gas. These are fragile and wear out with use, and a crack can stop the furnace cold. Older furnaces may use a standing pilot with a thermocouple, which can fail to hold the gas valve open once it weakens.
The flame sensor sits in the burner flame and confirms that ignition happened. When it gets coated with residue, the furnace lights for a few seconds and then shuts off. Cleaning or replacing it is one of the most common repairs we make.
Draft and venting components
Before the burners light, the inducer motor pulls air through the heat exchanger and pushes exhaust up the flue. A pressure switch confirms that draft exists. If the inducer is weak, the vent is blocked, or the small rubber hose to the switch has cracked, the furnace will not proceed to ignition.
- Inducer motor bearings that squeal or seize
- Pressure switch hoses that crack in hot attics
- Flue pipes with loose joints or improper slope
- Vent caps blocked by debris, leaves or nesting birds
- Condensate traps on high-efficiency furnaces that clog and trip the pressure switch
Controls and safety limits
The control board orchestrates everything and reports faults through a blinking light. Boards can fail from power surges, moisture or age. Around it are safety devices: a high-limit switch that shuts the burners off if the heat exchanger overheats, and rollout switches that trip if flames escape the burner area.
A tripped limit is a symptom, not the root cause. Overheating usually traces back to restricted airflow from a clogged filter, closed registers or a dirty blower. Flame rollout can point to a blocked heat exchanger or venting problem and is treated as a safety issue.
The blower and airflow
The blower moves heated air through the ducts. Its motor, capacitor and wheel all wear over time. A blower wheel caked with dust moves far less air, which can trigger the high limit and make the house feel lukewarm. In multi-story homes, we also look at whether ducts serving upstairs rooms are connected and insulated, since a loose attic duct can make a healthy furnace seem weak.
Repair decisions and replacement rules
Once we have found the failed component, we explain the repair and what else we noticed. If the heat exchanger is cracked or the furnace needs repeated major repairs, replacement may be the better choice. When that comes up, it is important to know that South Coast AQMD Rule 1111 limits NOx emissions from gas fan-type central furnaces sold and installed in this region, and the district has been amending it toward zero-emission requirements. We check the current rule before recommending a new gas furnace, and we can show you a heat pump option for comparison.
If a carbon monoxide alarm sounds or you smell gas, leave the home and contact the gas utility or emergency services first. We serve San Gabriel, South Pasadena, Alhambra, Temple City and Rosemead in addition to San Marino.
More services in San Marino
- AC Repair in San Marino
- Heating Repair in San Marino
- Heat Pump Installation in San Marino
- AC Installation in San Marino