Homeowner guide · Water heaters
How to flush a water heater, and why sediment matters
To flush a water heater, you open the drain valve near the bottom of the tank and let water run until it comes out clear. How often depends on how hard your water is. Here are the steps from public guidance, the safety precautions, and who should leave the job to a plumber.
Key takeaways
The short version
- Sediment buildup can promote the growth of waterborne bacteria, the NJ Department of Health says.
- Drain from the valve near the bottom of the tank until the water runs clear.
- Hard-water areas may need flushing as often as monthly; others only yearly.
- Check the temperature and pressure relief valve once a year.
- People 50 or older, smokers, and anyone with a weakened immune system or chronic lung disease should not flush the heater themselves.
Why flushing matters
Minerals in the water settle at the bottom of a tank water heater as sediment. The New Jersey Department of Health says sediment buildup can promote the growth of waterborne bacteria, which can cause illnesses such as Legionnaires’ disease (NJ Department of Health).
Tredyffrin and Easttown homeowners dealing with scale should also read our hard water guide, since water hardness drives how often you need to flush.
Who should not do this themselves
The NJ Department of Health says people at increased risk should not take part in draining and flushing a water heater, because of exposure to aerosolized water. That includes people 50 or older, smokers, and anyone with a weakened immune system or chronic lung disease (NJ Department of Health). If that describes anyone doing the work, have a plumber flush the tank.
The steps
- Read your heater’s manufacturer instructions first. The NJ guidance says to follow them.
- To reduce scald risk, the NJ guidance says to run hot water at the faucets so the hot water in the tank is replaced with cold.
- Find the drain valve near the bottom of the tank.
- If the valve has not been used in years, attach a garden hose first, in case it is hard to close afterward, as Montana’s program advises.
- Open the valve and drain into a bucket, or through the hose to a safe drain, until the water runs clear.
- Close the valve, refill the tank, and restore power or gas according to the manufacturer’s instructions.
The NJ guidance says the water can be very hot, and suggests protective goggles and heavy-duty rubber gloves (NJ Department of Health).
How often to flush
Montana’s weatherization program says it depends on local water hardness: in some areas monthly flushing is recommended, while others need only annual flushing (Montana Weatherization / MSU Extension).
| Your water | Starting point |
|---|---|
| Hard water, visible scale on fixtures | Flush more often; ask a plumber to check sediment at your first visit |
| Softer water or a water softener | Once a year is a reasonable start |
| Unsure | Check your water hardness, then decide |
The table is our practical starting point based on Montana’s guidance, not a fixed rule.
The once-a-year relief valve check
The temperature and pressure relief valve lets water out if the tank gets too hot or the pressure too high. Montana’s program says it should be checked annually to make sure it works (Montana Weatherization / MSU Extension). A valve that drips constantly or will not reseat after testing needs a plumber.
When to call
Rather not drain it yourself?
We flush tanks, test relief valves and replace water heaters in Wayne, Strafford, Paoli, Chesterbrook, Berwyn and Devon. Call (610) 788-0042.
Frequently asked questions
Water heater flushing questions
Answers by John, Tredyffrin Easttown Plumber.
How often should I flush my water heater?
It depends on your water hardness. Montana’s weatherization program says some areas need monthly flushing and others only annual flushing.
Why flush a water heater?
The NJ Department of Health says sediment buildup can promote the growth of waterborne bacteria, which can cause illnesses such as Legionnaires’ disease.
Who should not flush a water heater?
The NJ Department of Health says people at increased risk, including those 50 or older, smokers, and anyone with a weakened immune system or chronic lung disease, should not take part.
How do I know when the tank is flushed?
Montana’s program says to drain until the water runs clear.
How often should I test the relief valve?
Montana’s weatherization program says the temperature and pressure relief valve should be checked annually.
Does flushing apply to tankless water heaters?
Not covered by these sources. Follow your tankless heater manufacturer’s maintenance instructions.
Sources
Where these facts come from
Every figure and rule in this guide comes from the public sources below. Rules and fees can change, so confirm with the source before you act.
Keep reading
Related services and guides
Water heater temperature
Why 120°F is the usual setting.
Hard water in T/E
Scale, fixtures and heaters.
Water heater installation
Gas and electric replacements.
Emergency plumber
Leaking tank or no hot water.
Our service area
Plumbing across Tredyffrin Township, PA
Tredyffrin Easttown Plumber serves every neighborhood in Tredyffrin Township, including Wayne, Strafford, Chesterbrook, Paoli, Berwyn, Devon, Daylesford, and Howellville, plus neighboring Easttown Township. Our office is at 217 Conestoga Rd, Suite 10, Wayne, PA 19087.
