Equipment
- Ruud gas furnace
- Replaced failed flame sensor
- Cleaned restricted airflow components
- Verified ignition and heat distribution
What the customer reported
A second Ruud furnace repair in Alamo, different house, different street, different symptom pattern than the inducer-motor job on Castle Crest Rd. This customer’s furnace was running but not maintaining consistent indoor temperature. Some rooms held setpoint, others stayed cool. Heating bills had climbed even though the furnace seemed to be working.
What we found
The symptom pattern said “intermittent heating performance”, and the diagnostic walked through every component that could produce that. We checked the ignition system, flame sensor, gas valve, blower motor, and control board systematically. Two failures had stacked:
- Failing flame sensor: the flame sensor is the small metal rod that confirms the burner is actually lit. When it gets coated with combustion residue (which happens slowly over a few seasons), it sends an unreliable signal to the control board. The board then shuts the burner down intermittently as a safety response. That’s the “running but not maintaining temperature” pattern.
- Restricted airflow in the blower assembly, accumulated dust and debris on the blower wheel and limited intake airflow at the filter side. Reduced airflow means the heat exchanger overheats and trips its high-limit safety control, which adds to the intermittent-shutdown pattern.
Two issues, one diagnostic visit. The flame sensor was the primary fault; the airflow restriction was making it worse.
What we did
- Replaced the failed flame sensor with a model-matched Ruud part
- Cleaned the blower wheel, the blower housing, the heat-exchanger surface accessible from the burner side, and the filter rack
- Verified gas valve operation and burner ignition through multiple cycles
- Re-balanced airflow and confirmed normal heat distribution throughout the house
The detail that mattered
The flame sensor part itself is inexpensive, under $50. The diagnostic work to isolate it as THE cause (vs gas valve, vs control board, vs other plausible-but-wrong suspects) is what makes the repair stick. A shotgun-replace approach: “we replaced the gas valve and the control board and the flame sensor, $1,200 please”, would have worked too, eventually, but at much higher cost and longer time. We diagnose, then fix.
What the homeowner got
Furnace restored to reliable operation, consistent indoor temperature across rooms, and safety controls verified. The cleaning side of the work also bought the customer additional service life on the blower motor (running it in a debris-clogged housing shortens its life materially). 1-year warranty on the repair work.
The photos below show the disassembly, component inspection, and the gas-valve check during the diagnostic.
Photos
