Residential No-Heat — Gas Furnace Short Cycling on Ignition
Homeowner reports intermittent no-heat. The furnace lights, runs for a few seconds, then shuts down and tries again. Unit: 80% efficiency single-stage gas furnace, hot surface ignition, 11 years old. This is a graded decision lab from Residential HVAC Service & Diagnostics — you choose each next check, readings fill in as you work, wrong turns are coached, and you are scored on cause, efficiency, safety and verification. It runs inside HVAC Technical Training — Paths A–D, about 15 minutes.
- Interactive decision labs
- Built by working technicians
- Path-based verifiable certificate
- Exam preparation only
- Worldwide online
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Where this lab sits
This is one module lab from Residential HVAC Service & Diagnostics. The full path builds the rest of the diagnostic sequence around it, each module ending in a graded lab like this one.
Studying for an exam too?
Free practice questions with explained answers, then come back to the labs. Exam preparation only — we do not issue EPA, NATE or other official credentials.
All diagnostic labs
- Residential No-Cool — Split System Not Cooling
- Frozen Coil / Airflow Restriction
- Residential Over- and Undercharge — Poor Cooling Call
- Superheat / Subcooling Decision
- TXV Hunting — Temperature Swings
- Condenser / High Head — Walk-in Cutting Out on High Pressure
- Rack — One Circuit Down (Case Group Warm)
- A2L Safe-Handling Decision (R-454B)
- Walk-in Cooler Not Holding Temperature
- Ice Machine Not Making Ice
- Reach-in / Prep Table Not Holding Temperature
- Walk-in Freezer Defrost Fault
- Natural Refrigerant Safe-Handling Decision
- Rooftop Unit Not Cooling
- RTU Economizer Stuck — No Free Cooling
- RTU High Static — Low Airflow and Poor Cooling
- RTU Gas Heat — No Heat / Ignition Fault
- RTU First Start-up Sequence
- No Cool, First Call — Work the Order
- Running But Only 8°F Split
- 28°F Split, Weak Air at the Registers
- Condenser Dead, Indoor Blower Running
- Ice on the Suction Line, Filter Black
- Short-Cycling After a Capacitor Swap
- Heat Pump Running on Strip Heat Only
- Inverter Mini-Split (R-32) Will Not Pull the Room Down
- Communicating RTU — No Cool, No Fault Code
- Occupied Retail, Warm Air, “The Last Tech Said It Was Fine”
- Leak Smell on a Current-Refrigerant System
- Commissioning Day — Drawings Versus As-Built