When the heat goes out in a San Lorenzo home, the furnace is rarely beyond saving. Most no-heat calls trace back to one part, such as an igniter, a dirty flame sensor, a pressure switch, a limit switch tripped by a clogged filter or a worn blower motor, and a technician can find which one with a few measurements. San Lorenzo is the unincorporated community just south of San Leandro, a short drive from our office, and we cover all of 94580 for heating, cooling and appliance repair.
Heating is most of the work here
San Lorenzo sits on the flat land near the bay, where cool, foggy mornings are common. Furnaces do most of their work from November to March and then sit idle through the summer. Many homes date from the post-war years, with a furnace in a hall closet or garage and ductwork running through the attic or crawlspace. That combination shapes what we find:
- a furnace that ran fine last winter and fails on the first cold night, after months of sitting unused;
- a filter forgotten over the summer that makes the furnace overheat and trip its high-limit switch once the heat runs for hours;
- crushed or disconnected duct runs, so one bedroom stays cold while the furnace works normally. That is a job for duct repair, not a new furnace.
Heater not working? What it usually means
| What the heater does | Likely cause | What it usually takes |
|---|---|---|
| Blower runs, burners never light | Igniter, pressure switch or inducer motor | Testing, then one part |
| Lights, then shuts off after a few seconds | Dirty or weak flame sensor | Cleaning or replacement |
| Runs a while, shuts down, restarts later | High-limit trip from a clogged filter or blocked vents | Filter, airflow check, limit test |
| Blows cool air between heating cycles | Thermostat fan set to On, not Auto | A setting change |
| Nothing at all, no fan and no lights | Power switch, breaker, door switch or control board | Electrical diagnosis |
Our furnace repair page goes deeper, and furnace not heating lists more checks you can do yourself.
Safe checks before you call
- Set the thermostat to Heat, a few degrees above room temperature, and replace its batteries if it uses them.
- Look at the filter. If it is grey and packed with dust, replace it.
- Make sure the furnace’s power switch (it looks like a light switch, on or near the unit) and its breaker are on.
- Check that the front panel of the furnace is fully seated. Many furnaces have a door switch that cuts power when the panel is loose.
- If the furnace has a small window with a blinking light, count the blinks. That code tells the technician where to start.
If you smell gas, do not touch light switches or the thermostat. Leave the house and call your gas utility or 911 from outside.
Repair or replace the furnace?
A furnace with one failed part and a sound heat exchanger is usually worth repairing. Replacement becomes the better choice when the heat exchanger is cracked, when the furnace has needed several repairs in a few winters, or when parts for an older model are hard to get. Our furnace repair-or-replace comparison walks through the decision. When replacement makes sense, we quote furnace installation, or a heat pump if you want heating and cooling from one system, with the price upfront and financing available. The furnace repair cost guide shows what usually drives the price of a repair.
Cooling and appliances too
Summers here are mild, but the warm spells of late summer and fall still find weak capacitors and dirty coils, so we handle AC repair and mini-split repair as well. We service the major furnace and AC brands, including Lennox, Goodman, Rheem and Bryant. In the kitchen and laundry room, we repair refrigerators, freezers and ice makers, ranges, ovens, dishwashers, washers and dryers.
Where we work around San Lorenzo
We cover all of San Lorenzo (94580) and nearby Ashland and Cherryland, along with San Leandro and Castro Valley. Call before noon and same-day service is usually possible. Phone support is available 24/7.