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Here we explain just how to drain the water out of a water heater tank. This step is a necessary first step for several water heater maintenance and repair procedures such as water heater flush-out, water heater scale removal, or replacement of the water heater pressure-temperature relief valve.
The articles at this website will answer most questions about water heaters
as well as many other building plumbing system inspection or defect topics.
This page contains links to in-depth articles on inspecting, testing, and repairing problems residential hot water heaters of all types, including their parts, controls, and alternative sources for hot water as well as tips for improving hot water temperature, hot water pressure, and hot water quantity.
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We have a gas water heater. I’m a rather handy man. Would it be possible for me to flush it myself? What is a typical cost for this kind of service? - K.S., Seattle
Reply: Sure, if you're handy and careful, it's not difficult and not many tools are needed. But
Watch out: it's easy if nothing goes wrong (we list some things that can go wrong here and
at WATER HEATER DEBRIS FLUSH. And there are a few safety things to get right: avoiding being scalded, avoiding damaging a pressure/temperature relief valve, and avoiding flooding the home because of a snafu.
Tips On Draining the Water Heater Tank: Don't try opening the hot water tank drain valve without first noting these warnings and tips:
The water heater heat source should be turned off and the water tank cooled down (or run hot water out through building fixtures) before attempting to drain the tank - there can be a serious scalding hazard otherwise. If someone turns on electrical power to an electric water heater that is empty, it is likely that the heater electrodes will burn up.
You can connect a garden hose to drain the water heater tank to a suitable destination.
Use a pony pump if you need to drain "uphill" from the hot water tank to a suitable drain location. See PUMPS, PONY PUMPS for details.
If it's a Sunday - you may have trouble obtaining spare parts or emergency plumbing service if a problem occurs
Be sure to have a spare garden hose cap to install over the end of the drain valve in case it drips and won't shut off completely
If you have trouble turning the water heater tank drain valve to open it - don't force it - if break off the valve stem you may have a leak that you cannot shut off except by turning off cold water supply to the water heater
After opening the heater drain valve, if you forgot to turn off the cold water supply coming into the water heater, you may find that water just shoots out of the drain forever - you'll need to turn off the cold water supply to the water heater.
You will probably need to open a nearby hot water tap to let air into the plumbing system and through it into the water heater tank so that water can drain out at the tank's bottom. We don't recommend opening the pressure/temperature relief valve for this purpose as you may find that the TP valve won't shut successfully afterwards. Details about letting air into the water tank so that water can drain out are at WATER HEATER AIR INLET.
More details about draining and cleaning or de-scaling a hot water tank, including the removal of mineral or lime deposits and silt, are provided at WATER HEATER NOISE DIAGNOSIS, CURE where we describe water heater flushout and water heater scale removal.
If plastic water piping is installed, such as polybutylene water supply piping, it should be at least 18" from the water heater.
Water heater vacuum relief valves are required at water heaters in some communities, to protect against collapse of the water storage tank and to prevent backup of hot water into the cold water piping should cold water pressure drop. Here is Carson Dunlop's sketch of a vacuum relief valve.
What Goes Wrong When Draining the Water Heater Tank?
Watch out for these common problems that occur when you try to just drain a hot water heater tank:
Don't forget to turn off water coming into the water heater tank or you'll certainly never get it drained.
The water heater tank drain valve may be defective, may fail to open, or may fail to shut off, or worse, may break so that water comes blasting into the room where the heater is located. If this happens you will have to be able to turn off cold water coming into the water heater, and even so, water that is in the water heater tank and in building piping above the heater will drain backwards through the heater and onto the floor. Don't force any parts, especially parts on a plastic water heater drain valve.
Water heater tank drain valves are a pretty standard plumbing part. If your valve is worn or damaged, or if you just want to be extra safe, buy a replacement valve at a lumber or hardware supplier before starting your project. Most valves are standard 3/4" male pipe thread. You'll also need teflon tape or teflon pipe dope for the pipe threads.
The water heater cold water supply valve may not shut off: especially as that valve may not have been used for quite some time. Or you may not be able to turn the valve. Do not force the valve - you may break it. Sometimes we can loosen a recalcitrant water shutoff valve by a combination of a little squirt of WD-40 or a spray used by mechanics to free frozen nuts and bolts. Don't get these chemicals inside the water heater.
If your water heater supply valve won't turn off fully and is just dripping into the hot water tank, you can live with that during a water heater drain and repair project. If the valve won't turn off at all, you may have to turn off another supply valve upstream from the water tank, or possibly you'll need to turn off water supply to the whole building before starting your project.
If you run into trouble you won't want to have to leave the whole building water supply shut down, so having a few spare parts on hand to be able to close off the water heater itself (relief valve, tank drain valve) may be necessary.
The water heater relief valve may leak: often we use the test lever to allow air into the water heater tank during draining, as that will speed up the water heater tank drain process.
Watch out: But lifting the test lever can allow a bit of debris or even a damaged relief valve seat washer to flow out.
Where should the water heater draining garden hose drain-to? If you are routing a water heater drain hose to an indoor floor drain, be sure that drain is not clogged before beginning the project. Try pouring a bucket of water into the drain. If you are routing the water heater drain hose to outdoors, the water leaving the water heater tank should empty far enough from the building that it won't leak back into the structure through the foundation wall.
Question: no house water after replacing a water shutyoff valve and draining the hot water tank
(Mar 2, 2014) Anonymous said:
water shut off valve has been replaced after breaking. the hot water tank drained and i hooked water supply back to tank. now i get zero water in the house, but my water meter is sppining very slow
Anon: water meter spinning argues that there's a leak on the house side of the meter, or water is passing into the building and maybe a toilet is running; Yet you see "zero water" - you can start checking by turning off water at the main and looking at the meter to see if it stops; also if there are shutoffs that isolate different building areas those can narrow down the problem.
Finally, if the new water shutoff valve was installed using soldering and too much solder was pushed into a joint that could have blocked the valve. And of course, Make sure the valve is opened in the right direction.
This series of water heater maintenance and repair articles describes how to inspect, operate, diagnose, and repair electric hot water heaters.
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Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
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Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: email@example.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides extensive home inspection education and report writing material.
The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors. Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
TECHNICAL REFERENCE GUIDE to manufacturer's model and serial number information for heating and cooling equipment, useful for determining the age of heating boilers, furnaces, water heaters is provided by Carson Dunlop, Associates, Toronto - Carson Dunlop Weldon & Associates Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones