Tankless Water HeaterTroubleshooting2026-02-09
The Tankless Cold Water Sandwich Explained
A brief cold burst between hot draws is the 'cold water sandwich' — and recirculation can fix it.
If you feel a short blast of cold water shortly after hot water starts, you've met the 'cold water sandwich.' It's a known tankless quirk.
Why it happens
When hot water is used in quick succession, leftover warm water in the pipe is followed by a slug of cooler water before the unit fully reheats — felt as a brief cold spot.
How to reduce it
A recirculation system or a small buffer tank smooths delivery and largely eliminates the sandwich, giving more consistent hot water.
Key takeaways
- A brief cold spot between draws is normal
- Recirculation reduces or eliminates it
- A buffer tank also smooths delivery
- Correct sizing helps consistency
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