When water heats up, it expands a little. In most homes, that extra volume can go back toward the municipal supply. In others, the system is “closed” — and that's when an expansion tank becomes useful, and sometimes required.
What it does
The expansion tank (a small white vessel on the cold inlet) absorbs the pressure from thermal expansion. Without it on a closed system, the relief valve may drip more often and fittings work harder.
The 3 cases where the code requires it
Under Quebec plumbing code, thermal-expansion protection is required if any of these is on your water supply. Here's what they look like, so you can spot them easily:
Anti-return valve
Near the water inlet
Often near the meter
If you want us to install one, tell us in advance (when you request a quote or by calling). That way we plan it into the appointment — no surprise on install day.
Clues it may come up
- The relief valve drips regularly with no leak elsewhere
- You already know there's a PRV or check valve near the meter
- A recent upgrade closed the system (municipal work, etc.)