Lennox Boiler: Short-cycling
Short-cycling — firing for a minute or two then stopping, over and over — usually points to poor circulation, an output oversized for the load, a temperature-sensor fault, or flame instability on a Lennox boiler. It wastes gas and shortens the boiler’s life.
Short-cycling — firing for a minute or two then stopping, over and over — usually points to poor circulation, an output oversized for the load, a temperature-sensor fault, or flame instability on a Lennox boiler. It wastes gas and shortens the boiler’s life. On Lennox boilers, this is linked to 3 fault codes (Flame Failure, High Limit, Sensor Fault). Below are the likely causes, the safe checks you can make, and exactly what our licensed BC gas technicians do — because boiler repair in British Columbia is licensed gas work, not a DIY job.
This is a gas-safety fault. Diagnosing ignition, flame, gas or venting problems requires combustion analysis and gas-pressure testing that, by BC law, only a licensed gas technician may perform. Never bypass a safety lockout. Smell gas? Leave the building and call 911 or FortisBC at 1-800-663-9911 from outside.
What you might notice
- Boiler locks out under load
- Hot or burning smell near the unit
- Heat that starts then cuts out
- Erratic heating or hot-water temperature
- Boiler locks out or refuses to fire
- Wrong temperature shown on the display
Safe checks you can make first
These are the only steps a homeowner should take. If they don’t resolve it, stop — the rest is licensed gas work.
- 1Time how long it runs before stopping (under ~5 minutes is short-cycling)
- 2Check system pressure is in the normal 12–15 psi cold band
- 3Look for a fault code on the display
- 4Bleed radiators that are cold at the top — then call us if it continues
Related Lennox fault codes
These Lennox codes are commonly behind “short-cycling”. Tap any code for its full meaning, causes and fix.
What our licensed technicians do
- Check circulation: pump operation, air-bound zones, closed valves and flow rate
- Inspect the heat exchanger and strainer for blockage or scale
- Test the high-limit and supply/return temperature sensors
- Confirm correct system pressure and bleed trapped air
- Measure sensor resistance against the manufacturer temperature curve
- Inspect wiring, connectors and sensor mounting/contact
Lennox short-cycling — FAQ
Why does my Lennox boiler keep turning on and off (short-cycling)?
Short-cycling — firing for a minute or two then stopping, over and over — usually points to poor circulation, an output oversized for the load, a temperature-sensor fault, or flame instability on a Lennox boiler. It wastes gas and shortens the boiler’s life. The related Lennox fault codes are Flame Failure, High Limit, Sensor Fault. A licensed technician confirms the true root cause with the right instruments before any repair.
Is it safe to keep resetting my Lennox boiler when it shows "short-cycling"?
No. A single reset after a one-off event is fine, but "short-cycling" involves gas, ignition, flame or venting safety. Repeated resets without fixing the cause can be dangerous and can damage the boiler. If the fault returns, switch the boiler off and call GasBoilers.ca at 604-359-1081. If you ever smell gas, leave the building and call 911 or FortisBC at 1-800-663-9911 from outside.
Can you repair a Lennox boiler with this problem in Greater Vancouver?
Yes. Our Red Seal–certified, TSBC gas-licensed technicians diagnose and repair Lennox GWB8-IH gas-fired hot water boilers across Vancouver, Burnaby, Surrey, Richmond, the Tri-Cities and the rest of Greater Vancouver. Same-day appointments are often available — call 604-359-1081.
“Short-cycling” on other boiler brands
Lennox boiler short-cycling? We can help today.
Licensed, Red Seal–certified gas technicians across Greater Vancouver. Upfront pricing, same-day service available.