The short answer
When your water heater warms a tank of water, the water expands. On most Bend homes it can’t push back into the city main, because the City installs and owns a backflow assembly at every residential meter. Without an expansion tank, that extra volume spikes the pressure in your pipes every time the heater runs. The City of Bend says that if you are replacing or adding a water heater, an expansion tank is required.
See who to call ↓Signs your expansion tank or pressure is the problem
- The temperature and pressure (T&P) relief valve on the water heater drips or has a wet drain line.
- Faucets spit or toilets run for a moment after the heater has been running.
- Pipes bang or hammer when a valve shuts quickly (dishwasher, washer, sprinklers).
- The expansion tank sounds full of water when you tap it, or water comes out of the air valve when you press it. That usually means the internal bladder has failed.
- Water pressure feels very strong at every fixture, or hose bibs blast.
- Toilet fill valves, faucet cartridges or the water heater itself keep wearing out early.
Only in Bend
What’s different here
The backflow assembly at your meter makes your plumbing a “closed system”
The City of Bend says the backflow device on the water meter is owned, maintained and tested each year by the City. It protects the public water supply, but it also stops heated, expanded water from pushing back toward the main. Plumbers call that a closed system, and it’s exactly the situation thermal expansion tanks are made for.
Avion and Roats Water customers have different setups, so ask your provider, but the same physics apply whenever there’s a check valve or backflow preventer between your house and the main.
Bend is built on buttes, so pressure varies by neighborhood
The City runs its water system in pressure zones separated by pressure reducing valves in the street, because Bend climbs from the river up Awbrey Butte, Overturf Butte, Pilot Butte and the west-side ridges. What reaches your house depends on your zone and where you sit in it. Homes low in a zone can see noticeably higher static pressure than neighbors up the hill.
The plumbing code requires a pressure reducing valve (PRV) on the house when static pressure is over 80 psi. Many plumbers aim for roughly 50 to 70 psi inside the home. A $15 hose-bib gauge tells you where you are.
The tank and the PRV work as a pair
A PRV lowers incoming pressure, but it also acts like a check valve, so a house with a PRV needs expansion control too. The expansion tank’s air precharge should be set to match your actual house pressure (after the PRV) before it’s installed. A tank precharged at the factory 40 psi on an 80 psi house fills with water and does very little.
Water is soft here, so tanks tend to last
City of Bend water is soft to slightly hard (about 1 to 1.5 grains per gallon), so scale isn’t usually what kills the tank or the heater. Bladder failure and wrong precharge are. Expect to replace an expansion tank every 5 to 10 years, often at the same time as the water heater.
Bend plumbers for expansion tanks, PRVs and pressure problems
Any licensed plumber can install an expansion tank or PRV. These Bend companies list water heaters or water-pressure work on their own sites.
Sunset Plumbing of Bend
62979 Plateau Dr #1, Bend
Water heaters, gas lines, repiping and general repairs
Serving Bend since 1982.
CCB #69172
Severson Plumbing
63110 Nels Anderson Rd, Bend (also Redmond)
Gas pipe installation, water heaters, camera and sewer line inspections, emergency service
Family-run since 1977.
CCB #63655
Deschutes Plumbing Company
930 SE Textron St, Ste B, Bend
Gas piping, water heaters, drain cleaning and general plumbing
Renew Plumbing Services
Bend and Central Oregon
High and low water pressure, leak and gas detection, sewer repair and locating
CCB #116029
Central Oregon Heating, Cooling, Plumbing & Electrical
840 SE Woodland Blvd #135, Bend (plus Redmond, Madras)
Plumbing alongside HVAC and electrical, 24/7 emergency service
Listed in no particular order. Services were checked on each company’s own website on Oct. 27, 2026. Verify any contractor’s license on the Oregon CCB site. Need a general plumber? Compare all Bend plumbers.
Check it yourself in 10 minutes
- Screw a pressure gauge (hardware stores sell them for hose bibs) onto an outside spigot or the water heater drain, with no water running in the house.
- Read the static pressure. Under 80 psi is within code; 50 to 70 is the comfortable range.
- Leave the gauge on overnight if it has a red “max” needle. If the needle climbs well above the starting number after the heater runs, you have thermal expansion.
- Tap the expansion tank: the top half should sound hollow. If it sounds solid all the way up, the bladder has likely failed.
- Look at the T&P valve drain line on the water heater. Water there is a warning, not normal.
Questions to ask before you hire
Ask
- What is my static pressure, and will you leave me the reading?
- Is my PRV adjustable, and what will you set it to?
- Will you set the expansion tank’s precharge to my house pressure before installing it?
- Is the tank sized for my water heater’s gallons and my pressure?
- Does the price include the plumbing permit (if it’s part of a water heater job)?
- Where will the tank be supported? Tanks shouldn’t hang off the pipe alone.
Red flags
- A new water heater installed in Bend without an expansion tank.
- Replacing a dripping T&P valve over and over without checking pressure.
- A PRV set by feel, with no gauge reading.
- Pushing a whole-house water softener as the fix for pressure or relief-valve problems.
Common questions
Do I need an expansion tank in Bend?
If you have a tank water heater on City of Bend water, almost certainly. The City says an expansion tank is required when you replace or add a water heater, and every residential meter has a City-owned backflow assembly that keeps expanded water from flowing back to the main.
How much does an expansion tank cost?
The tank itself is usually under $100 at a supply house. Installed prices from Bend plumbers vary with access and whether it’s part of a water heater replacement, so get a written quote. It’s often cheapest to add when the water heater is replaced.
What water pressure is too high?
Oregon’s plumbing code requires a pressure reducing valve when static pressure is above 80 psi. Many plumbers target 50 to 70 psi inside the house.
How long does an expansion tank last?
Commonly 5 to 10 years. When the internal bladder fails, the tank fills with water and stops working; a tank that sounds solid when tapped, or leaks water from the air valve, needs replacing.
Does a tankless water heater need an expansion tank?
Tankless heaters hold very little water, so thermal expansion is much smaller. Your plumber and the manufacturer’s instructions decide; on a closed system many plumbers still add a small tank.
