The short answer
A furnace that will not heat has usually failed at one step of its start-up sequence, such as the inducer, igniter, gas valve, flame sensor or blower. We find the failed step, repair it, check venting and safety controls, and explain whether repair or replacement makes more sense.
A gas furnace follows the same sequence every time it starts: the thermostat calls for heat, the inducer fan clears the flue, the igniter heats up, the gas valve opens, the flame sensor confirms ignition and, after a short delay, the blower begins sending warm air through the house. When a Menlo Park furnace fails, it almost always breaks down at one specific step in that chain, and finding which step is the fastest way to a correct repair. ExpertFlow HVAC Repair Service, based about nine miles south in Los Altos, repairs gas furnaces throughout the 94025 area. This page walks through that start-up sequence, what goes wrong at each stage, and how to weigh a repair against replacement now that the Bay Area's furnace rules are changing.
Where in the sequence did it stop?
You can often tell roughly where the problem lies just by watching and listening when the heat is called for. Note what happens and in what order, because it is the most useful information you can give a technician.
- Nothing happens at all: thermostat, power, a tripped breaker, a door safety switch or a blown control fuse.
- The inducer runs but there is no glow or spark: a pressure switch, blocked vent or failed igniter.
- The igniter glows but no flame appears: a gas supply issue or a failed gas valve.
- Flame lights and goes out within seconds: most often a dirty or failing flame sensor.
- Flame stays lit but no air comes out: a blower motor, capacitor or control board problem.
- Air comes out but feels cool: a limit switch trip from overheating, often caused by a clogged filter.
Older ducts and furnace closets
Many Menlo Park homes have furnaces in hall closets, garages or crawlspaces, connected to ducts that have been in place for a long time. Over the years, duct joints separate, insulation sags and returns get partly blocked during remodels. Those problems do not stop a furnace from running, but they can make it overheat, short cycle or fail to warm distant rooms.
Closet furnaces also need enough combustion air. If the closet door has been replaced with a solid one or the space is packed with storage, the furnace may not burn cleanly. We check combustion air supply, return air size and duct condition as part of a full diagnosis.
Safety checks we never skip
Every repair includes a check of the parts that protect your household. We measure gas pressure, observe the burner flame, confirm the vent is drafting properly and inspect accessible areas of the heat exchanger for cracks or corrosion. Limit and rollout switches are tested to make sure they will shut the furnace down if something goes wrong.
If we find a condition that could let carbon monoxide into the home, we explain what we found and advise keeping the furnace off until it is fixed. A working CO alarm near sleeping areas is essential in any home with gas appliances.
Repair or replace under the new rules
Most furnace issues, such as a sensor, igniter, pressure switch or capacitor, are well worth repairing. The decision gets harder when a furnace is old, needs a major part like a heat exchanger or control board, and has needed frequent repairs.
The regulatory picture matters here. Under Bay Area Air District Rule 9-4, natural gas furnaces manufactured from 2029 must meet a zero-NOx emission standard, which in practice points homeowners toward heat pumps when they replace a furnace after that date. The rules do not require replacing equipment that works; they apply only when a furnace fails or is replaced. So keeping a furnace running with a sensible repair is entirely reasonable.
If you are leaning toward replacement, we can compare a new furnace with a heat pump side by side. For heat pumps, BayREN and your local clean energy provider may have incentives, which we confirm before quoting because offers change by funding cycle.
Keeping your furnace ready
Replace the filter at the start of the heating season and regularly after that. Keep the area around the furnace clear, and make sure supply and return grilles are not blocked by rugs or furniture. A fall tune-up gives a technician the chance to clean the flame sensor, test the igniter and safety controls and check the venting before the coldest nights. We also repair furnaces in East Palo Alto, Atherton, Palo Alto, Mountain View and Los Altos Hills.
More services in Menlo Park
- AC Repair in Menlo Park
- Heating Repair in Menlo Park
- Heat Pump Installation in Menlo Park
- AC Installation in Menlo Park
