Dunkirk Error E18: Supply water over-temperature / thermal overrun
Per the Q90/95M-200 manual, hard-lockout Code 18 (Thermal Overrun, Level 2) means supply/outlet water exceeded ~200F; the milder Level 1 shows soft-lockout b18 (burner held off until outlet drops ~9F below target, soft-lockout threshold ~183-203F). Display flashes 'E18'; manual RESET required. We diagnose and repair it across Greater Vancouver — same-day and after-hours.
Per the Q90/95M-200 manual, hard-lockout Code 18 (Thermal Overrun, Level 2) means supply/outlet water exceeded ~200F; the milder Level 1 shows soft-lockout b18 (burner held off until outlet drops ~9F below target, soft-lockout threshold ~183-203F). Display flashes 'E18'; manual RESET required.
Dunkirk fault codes can vary by model and series. Use this as a guide — the same code can have more than one cause. Our Technical Safety BC–licensed technicians read the code, confirm it against your unit's manual, and diagnose the true cause before any repair.
Likely causes of Dunkirk error E18
- Low water flow through the boiler (failed/air-bound circulator, dirty system)
- Closed valves or undersized circulator on a small zone
- Air trapped in the heat exchanger
- Failed or out-of-range outlet/supply temperature sensor
- System low on water or low pressure
What you can safely check
- Check system pressure is in the normal 12-15 psi cold range
- Confirm the circulator is running and zone valves are open
Beyond these checks, do not open the unit or touch gas/electrical parts — BC law requires a licensed gas fitter. Call us for a proper diagnosis.
Error E18 usually leaves you without heat or hot water and can indicate a safety-related fault. Don't keep resetting it — call for priority after-hours Dunkirk repair.
Parts Are Professionally Installed — Not Sold for DIY
For your safety and to keep your manufacturer warranty valid, BoilerPart.ca does not sell loose boiler parts over the counter or for self-installation. Under BC regulations, gas appliance components must be installed by a licensed gas fitter. Every part we source is genuine OEM and is professionally fitted, tested, and certified by our Technical Safety BC–licensed technicians as part of a complete repair or installation.
Parts often behind Dunkirk error E18
Genuine Dunkirk parts we supply and professionally install — never for DIY.
Our Guarantees & Warranties
Every repair and installation is backed by genuine parts, licensed workmanship, and a promise to make it right.
Workmanship Guarantee
Every repair and installation is backed by our written workmanship guarantee. If a part we installed fails because of our work, we make it right.
Genuine OEM Parts
We fit only manufacturer-original (OEM) components so your boiler performs to spec and keeps its factory warranty intact.
Manufacturer Warranty Honoured
As an authorised service provider for the brands we work on, our installs preserve and register your manufacturer parts warranty.
Licensed & Insured
All work is completed by Technical Safety BC–licensed gas fitters (Licence LGA0043870, Boiler Permit LBP0046450). We are fully licensed, bonded and insured for your protection.
Up-Front Pricing
You approve the diagnosis and quote before any work begins. No hidden fees and no surprise charges.
Satisfaction Commitment
Backed by the full HVAC resources of CanroHeat.ca and four decades of service in Greater Vancouver since 1985.
Dunkirk Error E18 Repair Across Metro Vancouver
Frequently Asked Questions
Fix Dunkirk Error E18 Today
Licensed Dunkirk diagnosis and repair with genuine parts — same-day and after-hours across Greater Vancouver.
A Division of CanroHeat.ca · Licensed Gas Fitters · Serving Greater Vancouver since 1985