Vaillant Error F.20: Safety temperature limiter
Safety switch-off by the temperature limiter — the safety thermal cut-out has operated and shut the boiler off because a temperature limit was exceeded. We diagnose and repair it across Greater Vancouver — same-day and after-hours.
Safety switch-off by the temperature limiter — the safety thermal cut-out has operated and shut the boiler off because a temperature limit was exceeded.
Vaillant 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 Vaillant error F.20
- Flow NTC sensor not correctly thermally connected or defective
- Boiler overheated due to poor circulation
- Pump fault or blockage restricting flow
- Faulty high-limit thermostat / safety cut-out
- Air in the system or closed isolation valves
What you can safely check
- Check the pressure gauge reads roughly 1.0–1.5 bar when cold
- Confirm radiators are not all turned off (the system needs somewhere for heat to go)
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 F.20 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 Vaillant repair.
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Parts often behind Vaillant error F.20
Genuine Vaillant parts we supply and professionally install — never for DIY.
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Vaillant Error F.20 Repair Across Metro Vancouver
Frequently Asked Questions
Fix Vaillant Error F.20 Today
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