BoilerTroubleshooting2026-02-26
Boiler Won't Stay Lit: Causes
A boiler that fires then cuts out points to the flame sensor, gas supply or condensate.
When your boiler ignites but won't stay lit, the flame-proving system is usually involved.
Common causes
A dirty flame sensor, low gas pressure, a blocked condensate pipe, or a faulty gas valve cause the boiler to drop out seconds after ignition.
What to do
Check for a frozen or blocked condensate pipe in cold weather; otherwise the flame sensor or gas valve needs a technician — don't keep resetting.
Key takeaways
- Fires then cuts out = flame-proving fault
- Check the condensate pipe in winter
- Don't repeatedly reset
- Flame sensor cleaning often fixes it
Need help with your boiler?
Licensed, gas-certified technicians serving Greater Vancouver since 1999. CombiBoiler.ca — A division of ROMA Heating Ltd..
Frequently asked questions
More Boiler articles
Boiler Leaking Water: Causes and RepairsBoiler leaks usually come from the pressure-relief valve, pump seals, fittings or the heat exchanger.Boiler No Heat: Emergency TroubleshootingNo heat from a boiler is often pressure, ignition, a pump or a tripped lockout — here's how to check.Why Your Boiler Keeps Losing PressureRecurring pressure loss usually means a leak, a failed relief valve, or a waterlogged expansion vessel.Boiler No Hot Water: Common CausesHeating works but taps run cold? Suspect the diverter valve, flow sensor or plate heat exchanger.Boiler Kettling and Banging Noises ExplainedThat rumbling 'kettle' sound usually means limescale or sludge in the heat exchanger.Combi vs Conventional Boiler: Which Is Best?Combi boilers save space and give on-demand hot water; conventional systems suit high simultaneous demand.
More from our knowledge base
Furnace Won't Turn On? Causes and FixesFurnaceFurnace Blowing Cold Air: What to CheckFurnaceWhy Your Furnace Short-Cycles (and How to Stop It)FurnaceNo Heat? Emergency Furnace Repair GuideFurnaceFurnace Making Strange Noises: A Sound-by-Sound GuideFurnaceAnnual Furnace Maintenance ChecklistFurnaceAll ArticlesBrowse the full library