Where gas furnaces fail
- Hot surface igniter
- Igniters are consumable. A cracked or aged igniter is one of the most common no heat causes and is a straightforward same visit repair.
- Flame sensor
- A fouled sensor produces a weak flame signal, so the control board closes the gas valve seconds after lighting. Symptom: the burner lights, then shuts off, sometimes repeatedly.
- Pressure switch and inducer
- A failing inducer motor or a blocked vent or condensate path prevents the pressure switch from closing, so the sequence never reaches ignition.
- Gas valve and control board
- Less common than the parts above, but both fail. Diagnosis relies on verifying every input before condemning the component.
- High limit and rollout switches
- These trip for a reason. A tripped limit means airflow is restricted. A tripped rollout switch means combustion products are spilling and the appliance needs inspection before it runs again.
- Heat exchanger
- Cracks are a safety condition, not a comfort issue. If we find one, we shut the appliance down and explain the options.