Fall Furnace Tune-Up in Kirkwood and West St. Louis County
A fall furnace tune-up is the safety inspection that catches cracked heat exchangers before they vent carbon monoxide into the home. It’s also the preventive service that identifies degraded hot surface igniters, weakening flame sensors, and marginal capacitors during the off-peak service window before peak heating demand puts those failure modes under stress. The seasonal scheduling matters: tune-ups completed in September or October catch wear progression before the first cold snap brings the furnace into continuous operation. By the time a hot surface igniter fails on January 6 at 11 PM with single-digit outdoor temperatures, the parts truck is already booked and the household is shivering in 50°F interior conditions. An $129 fall tune-up in October prevents the $310 emergency repair in January, but the more important value is the heat exchanger borescope inspection that finds cracks before they become a carbon monoxide event.
The Fall Tune-Up Inspection Sequence
Every Purisync fall furnace tune-up follows the same 16-point inspection protocol regardless of equipment brand, age, or installation history:
1. Pre-Service Operation Baseline
System started at thermostat call for heat, allowed to reach steady-state operation (typically 5–10 minutes for forced-air furnaces), then baseline measurements taken before any service work begins.
2. Bacharach Fyrite Insight Plus Combustion Analysis
Combustion analyzer probe inserted in the flue at the equipment’s testing port. Measurements with the furnace at steady-state high-fire operation:
- CO air-free under 100 ppm — safe combustion threshold
- CO2 percentage 8–11% for natural gas residential equipment
- O2 percentage 4–9% for properly adjusted combustion
- Stack temperature within manufacturer-specified range
- Calculated combustion efficiency matching equipment’s AFUE rating
Combustion analysis results are documented on the work order. Equipment reading above 400 ppm CO air-free is shut down pending repair or component replacement. Equipment reading 100–400 ppm is documented as elevated and the customer receives written notice of the finding along with repair recommendations.
3. Spire Missouri Gas Pressure Verification
Testo 510i digital manometer measurements:
- Gas pressure at meter: 7" WC nominal, within Spire Missouri delivery specification
- Gas pressure at manifold post-regulator: 3.5" WC for single-stage natural gas burners (varies by equipment for two-stage and modulating)
- Gas valve operation verification across all stages on multi-stage equipment
4. Hawkeye Inspection Borescope — Heat Exchanger
Visual inspection of the heat exchanger interior using the Hawkeye borescope. This is the single most important inspection in the tune-up — cracked heat exchangers allow combustion products including carbon monoxide to mix with the supply air, posing a serious health and life-safety risk.
Inspection covers: visible cracks (any size is a replacement-warranting finding), carbon scoring from improper flame impingement, condensate damage on condensing equipment, and structural integrity of welds and joints. Photos and video documentation go on the work order. Findings are reviewed with the customer before tune-up completion.
5. Ignition Sequence Verification
Full ignition cycle observed: thermostat call recognized by control board, inducer motor starts and verifies pressure switch closure, hot surface igniter energizes and reaches ignition temperature (typically 2,000–2,500°F surface temperature, observable by glow color), gas valve opens, burner ignition occurs within manufacturer-specified time window (typically 3–7 seconds), flame sensor proves flame, and blower delay timer expires with blower energization.
6. Hot Surface Igniter Inspection
Visual inspection for physical damage (cracks in the ceramic body, broken nitride coatings, accumulated debris from gas line contaminants). Resistance measurement compared to manufacturer specification (typical 11–200 ohms depending on equipment). HSIs reading near the upper end of specification, or showing physical degradation, are flagged for proactive replacement during the tune-up if customer authorizes.
7. Flame Sensor Inspection and Cleaning
Visual inspection for oxidation on the sensor rod. Cleaning with fine steel wool or appropriate abrasive to restore conductive surface. Microamps measurement during burner operation (target 1–6 microamps; below 0.5 microamps indicates inadequate signal). Flame sensor cleaning is included in the tune-up scope at no additional cost; replacement is quoted separately if physical damage or inadequate signal after cleaning warrants it.
8. Pressure Switch Verification
Pressure switch operation verified during the inducer motor’s startup sequence. Switch closure threshold compared to manufacturer specification using the Testo 510i manometer reading inducer draft. Switches operating at the edge of specification are flagged for replacement.
9. Inducer Motor Service
Visual inspection for excessive bearing noise, vibration, or evidence of bearing wear. Amperage measurement during operation compared to nameplate. Motor housing temperature check during steady-state operation. Inducer motors showing degradation are flagged for proactive replacement before in-season failure.
10. Limit Switch and Safety Control Verification
High-limit switch continuity verification, manual trip and reset to verify operation. Roll-out switch verification (where equipped). Auxiliary limit switches (some equipment has multiple) verified for proper operation.
11. Blower Motor and Wheel Inspection
Blower wheel inspection for accumulated debris, balance, and free rotation. Motor amperage measurement at all operating speeds (or full ECM communication on variable-speed equipment). Motor bearing condition assessment. Blower wheel cleaning included in tune-up scope when debris accumulation affects airflow.
12. Static Pressure Measurement
Testo 510i digital manometer across the air handler measuring supply plenum and return plenum static pressures. Total external static pressure compared to design target: under 0.5" WC for standard residential blowers, under 0.8" WC for ECM variable-speed equipment.
13. Filter Replacement
Air filter replacement with appropriate MERV-rated filter for the equipment. Standard 1" pleated filter (MERV 8) included in tune-up scope. Higher MERV filters or oversized media filters available at additional cost. Filter replacement schedule recommendation provided based on observed dust loading.
14. Thermostat Verification
Thermostat reading compared to a calibrated reference thermometer at the same location. Battery replacement on battery-powered thermostats. Programming verification for programmable thermostats. Wi-Fi thermostat connection verification on smart thermostats.
15. Venting Inspection
Visual inspection of venting from equipment to outdoor termination. For 80% AFUE equipment: B-vent or chimney connector integrity, draft hood condition, chimney liner condition (where visible). For 92%+ AFUE equipment: PVC vent slope and termination, condensate slope back to drain, vent terminal clearance from intake and openings.
16. Documentation and Customer Report
Every measurement and observation goes on the work order: combustion analysis results, gas pressure readings, static pressure, heat exchanger borescope findings, component condition assessments. A copy of the completed tune-up checklist is provided to the customer along with maintenance recommendations and any flagged findings for proactive repair scheduling.
When to Schedule the Fall Tune-Up
The optimal scheduling window for fall furnace tune-ups is September 1 through October 31. This window catches the equipment before the first cold snap brings it into continuous operation, while parts availability is high and scheduling is flexible. By December 1, peak heating scheduling pressure has compressed the dispatch calendar, and emergency no-heat calls take priority over preventive tune-ups.
For customers with both an AC and a furnace, scheduling options:
- Spring AC tune-up: March or April
- Fall furnace tune-up: September or October
- Combined annual visit: single late-September or early-October visit covering both AC end-of-season check and furnace pre-season service. This works for stable equipment and saves $39 over separate visits ($219 combined vs. $129 + $129 separate).
Tune-Up Pricing
- Single furnace tune-up: $129. Covers all 16 inspection points above. Standard 1" MERV 8 filter included; higher MERV filters or oversized filters available at additional cost.
- AC + furnace combined tune-up: $219 (saves $39 vs. separate visits). Covers all inspection points on both pieces of equipment in a single visit.
- Maintenance plan members: tune-ups included at no additional charge. Maintenance plan details →
- Multi-system homes (2+ furnaces): $99 per additional unit when included with primary tune-up visit.
Pricing is for inspection and standard adjustments. Parts replacement (hot surface igniters, capacitors, pressure switches, etc.) is additional and quoted before installation. No upselling pressure during the tune-up visit. Findings are documented; replacement options are presented; customer decides.
Why Fall Tune-Ups Are Higher-Stakes Than Spring Tune-Ups
Spring AC tune-ups identify components nearing end of life that could fail during summer peak demand. Fall furnace tune-ups identify components nearing end of life plus safety issues that affect indoor air quality and life safety:
- Carbon monoxide production from cracked heat exchangers is a direct life-safety risk. Mild exposure causes headaches, fatigue, and confusion. Severe exposure causes loss of consciousness and death. Annual borescope inspection catches cracks before exposure occurs.
- Combustion safety verification through CO air-free measurement confirms the equipment is producing safe combustion gases that vent properly outside the home, not into the indoor environment.
- Gas line and connection inspection catches developing leaks before they become significant gas exposure risks (rare but possible failure mode).
- Polar Vortex preparedness. The January 2019, February 2021, and December 2022 stretches dropped temperatures into single digits and below. Furnaces running at near-design conditions for days at a time stress every component. Components flagged during fall tune-ups can be proactively replaced before the stretch begins.
Frequently Asked Questions
- How much does a furnace tune-up cost in Kirkwood?
- Standard single furnace tune-up is $129, covering 16 inspection points including combustion analysis (Bacharach Fyrite Insight Plus with target under 100 ppm CO air-free), gas pressure verification (Spire Missouri 7″ WC nominal, 3.5″ WC manifold), heat exchanger borescope inspection (Hawkeye scope), ignition sequence verification, hot surface igniter inspection, flame sensor cleaning, pressure switch and limit switch verification, blower and inducer motor service, static pressure measurement, filter replacement (standard 1″ MERV 8), thermostat verification, venting inspection, and complete documentation. AC + furnace combined tune-up is $219 (saves $39 vs. separate visits). Multi-system homes pay $99 per additional unit when included with the primary tune-up visit. Maintenance plan members receive tune-ups at no additional charge.
- When is the best time to schedule a fall furnace tune-up?
- September 1 through October 31 is the optimal window. This timing catches the equipment before the first cold snap brings it into continuous operation, while parts availability is high and scheduling is flexible. By December 1, peak heating scheduling pressure compresses the dispatch calendar and emergency no-heat calls take priority over preventive tune-ups. Late October is the latest practical scheduling without overlap into peak demand. Customers with both AC and furnace can either schedule separate spring AC and fall furnace tune-ups, or combine into a single late September visit (saves $39 vs. separate visits).
- What does Purisync’s fall furnace tune-up include?
- Sixteen inspection points: pre-service operation baseline, Bacharach combustion analysis with target under 100 ppm CO air-free, Spire Missouri gas pressure verification, Hawkeye heat exchanger borescope inspection (the single most important inspection for safety), ignition sequence verification, hot surface igniter inspection and resistance measurement, flame sensor cleaning, pressure switch verification, inducer motor service, limit and safety control verification, blower motor and wheel inspection, Testo 510i static pressure measurement, MERV 8 filter replacement, thermostat verification, venting inspection (B-vent/chimney for 80% AFUE, PVC vent slope and termination for 92%+ AFUE), and complete documentation. Every measurement goes on the work order with a copy provided to the customer.
- Why is the heat exchanger inspection so important?
- Cracked heat exchangers allow combustion products — including carbon monoxide — to mix with the supply air circulated throughout the home. Mild CO exposure causes headaches, fatigue, confusion, and flu-like symptoms; severe exposure causes loss of consciousness and death. Heat exchangers crack from thermal cycling stress (40+ years of expansion and contraction in older equipment), water damage from improper condensate handling (on condensing equipment), and manufacturing defects in specific equipment generations. Annual Hawkeye borescope inspection catches cracks before they’re producing dangerous CO levels. We document findings with photos and video; equipment with confirmed cracks is shut down pending replacement. This is one inspection where “I’m not sure, let’s wait until next year” is not an acceptable approach — life safety is on the line.
- What happens if the tune-up finds a problem with my furnace?
- If the tune-up identifies a significant issue (cracked heat exchanger, elevated CO production, failed component, marginal component, gas pressure outside specification), the finding is documented with measurements and photos, and the customer receives a written quote for the repair scope. For safety-critical findings (cracked heat exchanger producing dangerous CO, gas leak detected), the equipment is shut down pending repair and the customer receives explicit written notice. For non-safety findings (marginal component, MERV upgrade opportunity, ductwork issue), the tune-up itself completes and the repair is separately authorized and scheduled. For findings that compromise immediate operation, same-visit repair is offered if parts are available and the customer authorizes the work. No surprise charges added to the tune-up invoice without explicit authorization.
Contact Purisync Heating and Air
To schedule a fall furnace tune-up, contact our 325 N Kirkwood Road office at (314) 338-5111 or email info@purisyncheatingairconditioning.xyz. September and October scheduling is the priority window — book early to lock in your preferred date during the off-peak period before winter demand compresses our dispatch calendar.
- Emergency Line (24/7): (314) 338-5111
- Address: 325 N Kirkwood Rd #245, Kirkwood, MO 63122
- Email: info@purisyncheatingairconditioning.xyz
- St. Louis County Mechanical Contractor License: #MC-2014-08439-STL
- Kirkwood Business Registration: #BL-2014-1187
- EPA Section 608 Universal: #608U-2014-385721
Office Hours
- Emergency Service: 24 hours a day, 7 days a week
- Office Staff: Monday – Saturday, 9:00 AM – 5:00 PM
- Closed: Sundays and State/Federal Holidays (emergency line always active)