Vaillant Error F.23: Temperature difference
Safety switch-off due to water shortage — the temperature difference between the flow and return NTC sensors is too large, indicating poor or no circulation. We diagnose and repair it across Greater Vancouver — same-day and after-hours.
Safety switch-off due to water shortage — the temperature difference between the flow and return NTC sensors is too large, indicating poor or no circulation.
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.23
- Pump blocked, seized or running at insufficient output
- Air lock in the system
- Sludge / debris restricting flow through the heat exchanger
- Flow or return NTC sensor reading incorrectly
- Closed or partially closed isolation valves
What you can safely check
- Check system pressure on the gauge reads about 1.0–1.5 bar when cold
- Confirm any system isolation 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 F.23 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.23
Genuine Vaillant parts we supply and professionally install — never for DIY.
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Vaillant Error F.23 Repair Across Metro Vancouver
Frequently Asked Questions
Fix Vaillant Error F.23 Today
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