Protecting a water heater with a Therm-X-Trol expansion tank
Location: Mukilteo, WA
Service: Thermal expansion tank installation
Customer: Eileen L.
A Mukilteo homeowner recently called us to install a thermal expansion tank — specifically a Therm-X-Trol model. These tanks are a small but important part of a closed plumbing system, and when they fail or are missing entirely, the pressure buildup can shorten your water heater’s life or even cause damage.
We scheduled the work, showed up on time, and had Eileen’s new expansion tank installed and working the same day.
What Eileen Had to Say
“Great service and dependable plumbing company; JD is a pleasure to work with and they respond quickly.”
— Eileen L., Mukilteo
Thanks, Eileen. We appreciate the kind words — and quick response time is something we take seriously, especially here in Mukilteo where we’re already in town.
What Is a Thermal Expansion Tank?
When water heats up, it expands. In an “open” plumbing system, that extra volume just pushes back into the city water main — no problem. But most modern homes have a “closed” system with a backflow preventer or pressure-reducing valve that stops water from flowing backward.
In a closed system, the expanding water has nowhere to go. Pressure builds up every time the water heater cycles. Over time, this causes:
- Premature water heater failure — the tank is stressed with every heating cycle
- Dripping T&P relief valve — the temperature and pressure relief valve opens to release excess pressure
- Stress on pipes and fittings — repeated pressure spikes can cause leaks over time
A thermal expansion tank absorbs that extra volume. It’s a small tank (usually 2–5 gallons) with a rubber bladder inside. When the water heater heats up and pressure rises, the expanding water compresses the air in the bladder instead of stressing your plumbing.
Signs You Need an Expansion Tank
Not sure if your home needs one — or if your existing tank has failed? Here’s what to look for:
- T&P valve dripping or discharging — the relief valve on your water heater is releasing water to relieve pressure
- Water pressure fluctuates — pressure spikes when the water heater is running, drops when it’s not
- Water heater is newer but failing early — repeated thermal stress shortens tank life
- You have a pressure-reducing valve or backflow preventer — this usually means you have a closed system
- Existing expansion tank feels “waterlogged” — tap on it; if it sounds full of water instead of hollow, the bladder has failed
If your expansion tank is more than 5–10 years old, it’s worth having it checked. The bladder eventually wears out and the tank stops doing its job.
Why We Use Therm-X-Trol
We installed a Therm-X-Trol expansion tank for Eileen — it’s the brand we recommend most often. Therm-X-Trol tanks are:
- Stainless steel system connection — resists corrosion at the fitting
- Heavy-duty bladder — designed for potable water and long service life
- Properly sized for residential water heaters — we match the tank size to your water heater capacity and system pressure
There are cheaper expansion tanks on the market, but they tend to fail faster. A quality tank installed correctly should last 8–12 years.
Need an Expansion Tank Installed?
If your T&P valve is dripping, your water heater is failing early, or you’re not sure whether your home has the right expansion protection, give us a call. We serve Mukilteo and the surrounding area — and we’re already in town, so response time is fast.
Call 425-374-3909 · Request a Quote
Stollwerck Plumbing & Sewer · Mukilteo, WA · WA License #STOLLPL780CJ