FURNACE & AC · FURNACE REPAIR
Furnace Repair in Morgan Hill, CA
Is your furnace not heating or blowing cold air? Start with a measured diagnosis and safety checks: what can cause a gas furnace to fail, what a thorough heating service should include, and where safety changes the answer.
Quick answers
- Ignition components such as igniters and flame sensors are among the possible causes of furnace no-heat problems.
- Restricted return air can cause a furnace to run hot and trip the limit switch; diagnosis identifies whether that's occurring.
- A confirmed cracked heat exchanger means the furnace should stay off until it is properly addressed.
- Repeated electrical or safety-control trips should be diagnosed by a professional rather than reset repeatedly.
- Working carbon monoxide alarms are an important safety layer in homes with fuel-burning equipment.
Common furnace problems
Furnaces can develop a range of issues, and possible causes include ignition and flame-sensing components, blower motors, and controls or thermostats that were not set up correctly. Diagnosis is the way to determine which, if any, applies to a given system.
Furnace not heating
If the blower runs but the air stays cool, the burners are either failing to light or shutting down early. Possible causes include a flame sensor coated in oxide, a cracked or weak hot-surface igniter, a pressure switch responding to a blocked flue or condensate line, or gas-supply issues; a diagnosis identifies which one applies.
Furnace won't turn on
Thermostat mode and batteries, the service switch on the furnace, the breaker, and a fully seated blower door with its interlock switch are the quick checks. After that, control board faults, a failed transformer, or a blown low-voltage fuse are among the possible causes. If a breaker keeps tripping, stop operating the system and schedule qualified service rather than resetting it repeatedly — repeated trips can indicate an electrical fault.
Furnace short cycling
Repeated short runs can trace back to airflow — a loaded filter, closed registers, or return ducts undersized for the equipment — among other possible causes. The limit switch cuts the burners to protect the heat exchanger, so a pattern of tripping should be diagnosed rather than repeatedly reset.
Blower and airflow problems
A noisy startup, weak airflow at distant registers, or a blower that runs constantly can come from the motor, the capacitor, or the duct system rather than the furnace itself. Static pressure readings separate the two quickly — see do I need new ductwork?
What a professional heating diagnosis may include
Depending on the complaint, a diagnosis may include combustion and safety inspection, burner and flame-sensor cleaning, verification of the full ignition sequence, blower and static pressure readings, confirmation that safety switches operate, and examination of the visible heat exchanger and venting. Not every visit performs every item; scope follows the symptoms.
Repair or replace your furnace?
The decision comes down to the diagnosis, the scope and cost of the repair, the furnace's overall condition and repair history, parts availability, comfort, and how long you plan to stay in the home; age is context rather than the deciding factor. The picture changes when breakdowns start to repeat, when parts are discontinued or on long back-order, when one repair quote approaches a meaningful share of a new furnace, or when a heat exchanger crack is confirmed. The condition of the air conditioner that shares the indoor cabinet is also worth factoring in. Repair vs. replace covers the factors. If diagnosis leads to replacement, Morgan Hill permit requirements depend on the actual scope of that project — see Morgan Hill HVAC permits. When it's time, furnace installation explains the options, and replacing the furnace and AC together covers when doing both at once is the better project.
Cooling problems on the same system
In a central split system the indoor blower and ductwork are shared between heating and cooling. If the complaint is a warm house in July rather than a cold one in January, see AC repair in Morgan Hill.
Furnace not heating?
Tell us what it's doing and we'll get a service visit booked to diagnose it.
Common questions
My furnace starts and then shuts off after a minute.
Short cycling can have several possible causes, including restricted airflow, a dirty flame sensor, or a safety control doing its job. Several of those causes are combustion-safety related, so the fault should be diagnosed rather than repeatedly reset.
Why is my furnace blowing cold air?
If the blower runs but the air never warms, the burners are either not igniting or are shutting down on a safety limit. Possible causes include a dirty flame sensor, a failing igniter, or a blocked flue, and diagnosis is needed to confirm which applies.
The furnace won't turn on at all.
Check the thermostat mode and batteries, the switch on the furnace itself, the breaker, and whether the blower door is fully seated — many furnaces have an interlock switch there. Beyond that, control board and transformer faults are among the possible causes. If a breaker or safety control keeps tripping, don't keep resetting it — that can indicate an electrical or safety fault and calls for qualified service.
How often should a furnace be serviced?
Follow the maintenance guidance published by your furnace's manufacturer, plus any schedule in an existing maintenance agreement; beyond that, service needs depend on the furnace's condition and how heavily it is used. Depending on the visit, service may cover combustion and safety controls, burners and the flame sensor, the ignition sequence, blower and static pressure readings, and the visible heat exchanger and venting.
What should I do if I smell gas?
Stop using the system, leave the home, and call your gas utility from outside. Do not troubleshoot a suspected gas leak yourself.
When is a furnace not worth repairing?
A confirmed cracked heat exchanger takes the furnace out of service until it is properly addressed, and on many furnaces that leads to a replacement discussion. Diagnosis, repair scope and cost, parts availability, overall condition and repair history, comfort, and your plans for the home are the factors worth weighing against the cost of the repair; age is context rather than the deciding factor.