Flushing your water heater takes 45-90 minutes and removes the sediment that causes most tank failures. It's the single most impactful maintenance task for extending your unit's life — especially in San Dimas, where moderately hard water accelerates sediment buildup.
This guide walks you through the process step by step. If at any point you're not comfortable, or the drain valve is stuck, stop and call a professional. Forcing a stuck valve is the #1 way homeowners cause a leak during a DIY flush.
In this article
Why flushing matters
Every gallon of water that enters your tank leaves behind trace minerals — calcium, magnesium, and other sediment. Over time, this sediment settles on the bottom of the tank and hardens into a crusty layer.
That layer causes three problems:
- Noise — As water heats, moisture trapped under the sediment turns to steam and pops. That's the rumbling sound.
- Efficiency loss — Sediment insulates the tank floor from the burner, so the unit has to work harder to heat water.
- Premature failure — The overheating caused by sediment weakens the steel. Eventually, the tank cracks.
San Dimas specific: The water here is moderately hard. If you skip annual flushing, expect 3-5 years off your unit's lifespan. Flushing is not optional here — it's essential.
Tools and supplies you'll need
You probably have most of these. Nothing fancy required.
Optional: A wet/dry vacuum if the drain valve area is likely to splash. And a towel or two under the unit for drips.
Safety warnings — read first
Warning: The water in your tank is HOT. 120-140°F hot water can cause serious burns. Turn off the heat source and let the tank cool for at least 2 hours before draining. Do not skip this.
Warning: Don't force a stuck drain valve. If it won't open, stop. Forcing it can snap the valve, causing a major leak. Call a professional.
Warning: Don't drain onto landscaping or into a storm drain. Hot water and sediment can damage plants. Route the hose to a floor drain, utility sink, or outdoor area that can handle hot water.
Step-by-step instructions
Turn off the power or gas
Gas: Turn the gas valve knob to "pilot" or "off." Do not relight it yourself until the tank is refilled. Electric: Turn off the breaker at your electrical panel. You can also turn off the switch on the unit if it has one.
1 minuteTurn off the cold water supply
Find the cold water inlet valve at the top of the tank. Turn it clockwise to close. This stops new water from entering the tank while you drain it.
1 minuteLet the tank cool
Wait at least 2 hours. This is the most important safety step. Hot water from a tank can cause third-degree burns. Don't rush this.
2 hours (passive)Attach the garden hose to the drain valve
The drain valve is at the bottom of the tank. Screw the female end of your garden hose onto it. Route the other end to a safe drain — a utility sink, floor drain, or outdoor area that can handle hot water and sediment.
2 minutesOpen a hot water faucet
Open any hot water faucet in the house — a bathroom sink or tub works. This prevents a vacuum lock inside the tank, which would prevent proper draining.
30 secondsOpen the drain valve
Using the flat screwdriver or adjustable wrench (depending on your valve type), open the drain valve. Water will start flowing through the hose. Don't force it. If it won't open smoothly, stop and call a pro.
10-30 minutes (drain time)Flush with cold water (optional but recommended)
Once the tank is drained, briefly open the cold water supply for 10-15 seconds. This stirs up remaining sediment at the bottom of the tank and flushes it out through the hose. Then close the cold water supply again.
1 minuteClose the drain valve and refill
Close the drain valve tightly. Keep the hot water faucet open and reopen the cold water supply valve. Water will flow into the tank. Watch the open faucet — when water runs steadily with no air sputtering, the tank is full.
5-15 minutesRestore power or gas
Gas: Relight the pilot according to the instructions on the unit. Electric: Turn the breaker back on. Give the tank 30-45 minutes to heat the water before testing.
2 minutes + heat timeNot comfortable doing this yourself?
We'll connect you with a local provider who can schedule an annual flush — usually $100-$200.
Call (909) 488-7231After the flush: what to check
Once the tank is refilled and heated, check a few things:
- Hot water at the faucet — should be back to normal temperature
- No leaks around the drain valve — check 30 minutes after closing it
- No water dripping under the tank — dry the area and check again in 1 hour
- Reduced noise — if rumbling was the reason you flushed, it should be much quieter
If the noise doesn't go away after flushing, the tank may already be damaged. That's a sign the sediment has been there too long. Call a provider to assess.
When to call a pro instead
DIY flushing is fine for many homeowners — but there are situations where you should stop and call:
Call a pro if:
- The drain valve is stuck or won't open smoothly
- Your tank is over 10 years old (flushing can reveal existing damage)
- You see rust or corrosion on the tank body
- The unit is in a hard-to-reach location (attic, crawl space)
- You're not comfortable working around hot water or gas
- The flush reveals a leak or damage
Flushing FAQs
How often should I flush my water heater in San Dimas?
Once a year in San Dimas due to moderately hard water. Homes with very hard water may need it every 6 months.
How long does it take to flush a water heater?
Plan for 45-90 minutes total. Most of that is drain time. The actual hands-on work is 15-20 minutes.
What happens if I don't flush my water heater?
Sediment accumulates on the tank floor, causing rumbling noises, reduced efficiency, and eventually tank failure. Skipping annual flushing can shorten lifespan by 3-5 years.
Can flushing damage my water heater?
If done properly, no. If the drain valve is stuck and you force it, you can break the valve and cause a leak. On very old tanks with corroded bottoms, flushing can reveal existing damage.
Do I need to flush a tankless water heater?
No — but you need to descale it annually, which is a different process. Tankless descaling involves pumping a descaling solution through the heat exchanger. That's typically best left to a professional.
How much does a professional flush cost?
A standalone flush typically costs $100-$200 in San Dimas. Bundled with an annual maintenance visit, it's usually less.