A burner lights only when three conditions are met: a hot igniter, an open gas valve and proven draft. The board checks each, and if one is missing it holds the gas back.
Service · Alhambra, CA
Furnace Not Igniting in Alhambra, CA
A furnace that tries to light and cannot is stopping at the ignition stage of its sequence. The symptoms differ, a click, a glow or a silent igniter, and each narrows the cause.
What you are seeing
What the igniter is doing tells the story
- Glows orange, no flame
The igniter works but gas is not reaching the burners.
- Stays dark
The igniter has failed or the board is not sending it power.
- Clicks repeatedly
A spark system is firing without finding gas.
- Inducer runs, nothing follows
The pressure switch is not proving draft.
How it works
The three things ignition needs
A silicon carbide igniter is brittle and develops hairline cracks over many heating cycles. It can glow weakly, draw less current and fail to light the gas even though it looks fine.
The draft pressure switch is the third gatekeeper. A diaphragm closes only when the inducer pulls enough vacuum, so a brittle hose, a clogged port or a weak inducer wheel keeps the gas valve shut.
Property type
Standing pilots in older Alhambra heaters
Some original wall and floor heaters in 1930s and 1940s Alhambra bungalows use a standing pilot rather than an electronic igniter. A thermocouple holds the gas valve open only while the pilot flame heats it.
- Weak thermocouple
A worn tip cannot hold the valve and the pilot goes out.
- Dirty pilot orifice
Dust narrows the pilot flame.
- Drafts
Air from a cracked window or a flue can blow the pilot out.
Technique
How an ignition fault is isolated
Watch a start
A live heating call is followed stage by stage until the point where it stops.
Test the igniter
Resistance and current draw are compared with the part's rating.
Check valve voltage
The board should send voltage to the valve once the igniter is hot.
Prove the draft
The pressure switch and its hose are tested for closure and blockage.
Confirm supply
Gas pressure at the valve is measured with the furnace calling.
Tell the call whether the igniter glows, clicks or stays dark, and the fault can be narrowed.
(626) 687-0603Phase order
Igniter, valve, then supply
The igniter is the usual culprit and the easiest to confirm. The valve is tested next, and the gas supply last, since a supply problem would also show up at the stove and the water heater.
A furnace left locked out may also have collected soot at the burner ports, so the burners are cleaned when they are found dirty.
Local detail
Why ignition parts fail after a mild year
In a mild Alhambra winter an igniter may be heated only a few dozen times a year, yet it still ages in the closet or attic summer heat. Los Angeles County homes often find that out on the first cold night.
Measured results
What a clean ignition looks like
- First-try light
The burners light smoothly without a puff or a delay.
- Even flame
Blue flame along every burner with no lifting.
- Light-off timing
Flame is established within the trial period, with no repeated retries.
Safety protocol
Why repeated relighting is a hazard
- Gas buildup
Each failed attempt can release unburned gas into the burner box.
- Delayed ignition
Gas that collects and lights late can produce a damaging burst.
- Pilot relighting
Leave older pilots to a technician when they will not stay lit.
- Gas odor
Leave the house and call the gas utility and 911 from outside.
Triage order
Igniter, valve or board: which part is replaced
- Igniter
Replaced when resistance reads outside its range or the surface shows cracks.
- Gas valve
Replaced when it receives voltage at the right moment and still stays shut.
- Control board
Replaced when it fails to send power to the igniter or the valve at all.
- Pressure switch
Replaced when it will not close under a good draft, or its hose is repaired if it is split.
Scope: Emergency diagnostic dispatch, whole system replacement and ductwork replacement only. Scope and pricing are provided directly by independent licensed contractors.
Common questions
Questions about a furnace that will not ignite in Alhambra
Is ignition repair covered in 91801, 91803 and 91804?
Yes. This guidance applies to Alhambra homes in those three ZIP codes.
Why does the igniter glow but nothing lights?
Gas may not be reaching the burners because of a valve fault, a closed supply or a draft problem that stops the board from opening the valve.
Can an old igniter look fine and still be bad?
Yes. A cracked igniter can glow but draw too little current to light the gas.
Is it safe to relight a pilot myself?
Many manufacturers allow it, but a pilot that will not stay lit signals a fault, and a technician should find the cause.
A heating or cooling fault rarely fixes itself.
Call and describe the problem in Alhambra: what the system is doing, what it did first and how old the equipment is.