Gas Water Heater Replacement

10-easy-step guide

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Explore the gas water heater replacement guide with the DIY and how to do tips. Learn how to deal with a natural, propane gas and plumbing work, so you can save money and install a new unit properly.

Replacing a water heater is the last thing you want to hear when having a problem with hot water, leaking, corrosion or element failure.

First you will try to fix the problem. If your gas heater is leaking you will try to find where the leak is coming from. If the tank lining is corroded because of the aggressive hot water action, sorry to say, but you have to replace a water heater.

If your gas water heater is not producing enough hot water, it may suffer from sediment buildup (hard water) and rust. Recommendation is to drain and flush your gas appliance, but if it doesn't work... water heater replacement is what needs to be done. If you have a very old water heater, buying a new unit can be a good thing. New units are more energy efficient, they are equipped with the FVIR system, which protects the unit and the property from the accidental fire of the flammable vapors outside of the combustion chamber of the water heater and are less prone to corrosion.

Tools needed for gas water heater replacement

  • Pipe Wrench

  • Tongue and groove pliers

  • Hacksaw or pipe cutter

  • Unions, fittings or flex connectors

  • Teflon tape or joint compound

  • Thin wire

  • Soldering torch

  • Wire brush

  • Appliance dolly to change the old with a new heater

  • Garden hose

  • Level

  • Screwdriver

10 Easy Steps How To

I think this is the easiest and safest way to replace a water heater, a tank unit that is using propane / LP or natural gas.

Important: Take precautions when working with gas, it is really dangerous if gas is leaking. For the successful work you need basic plumbing and gas skills and the right tools.

Step 1. Drain the hot water tank

water heater drain valve

Your very first step in water heater replacement is to drain water from the tank. Use the main shut off water valve that supplies the home. Turn the gas valve off. Open the hot and cold faucets somewhere in the bathroom or kitchen above the unit (highest tap unit) and tap close to the unit (lowest point).

Take the garden hose and attached it to the water heater's drain valve located at the bottom. Open the drain valve and drain all the water from the tank.

Step 2. Remove the flue pipe

vent pipe

The tank's vent pipe is made of sheet metal segments connected to each other with the few screws. Separate the flue from the draft hood, and remove only those elements to free up some space for an easy access. Mark the elements if needed so you will know how to bring them back, in the right order.

Clean them off if they are covered with dust and other residues and be careful of bending it or modify any part of the duct. Replace the flue pipe if it is corroded.

emergency plumber

Step 3. Disconnect the gas line

gas line

Close the gas valve on both main supply line and gas control valve close to the unit, and double check is the element fully closed! To visually inspect is it disconnect it properly, check the pilot light, it should be out.

Either the gas heater uses a flexible gas line or rigid pipe (depends on local regulations), take the wrench to loosen the line union or disconnect the flexible gas line. Be very cautious during water heater replacement when dealing with the gas components.

Step 4. Disconnect the plumbing lines

water line

Make sure to remember or mark where the incoming cold water and the outgoing lines are. If your gas appliance is using the rigid galvanized pipe, simply open the unions close to the unit.

If using copper solid pipe cut the pipe just below the shutoff valve. Be sure to have the cut straight and take all the particles out. Prepare the copper pipe for soldering by removing burrs, polishing and applying soldering paste.

The easiest way is if the unit uses the flexible copper pipe, as it is very easy to disconnect it with a wrench.

Step 5. Remove the old unit

Make some room for the new gas heater, by moving the old unit out. The unit is heavy, especially if it had a problem with the sediment buildup, so use wisely all the help needed and dolly cart.

If you need a help to choose the right gas heater, there are some good information (a guide actually) how to choose the heater, money saving tips, reviews of different brands and manufacturers here, or if using the navigation bar with links to Rheem, AO Smith, and other manufacturers.

Bring the new unit in. If you were happy with the performance of the old unit, hot water production, recovery rate, efficiency; try to match features when buying a new unit. If the size and features are the same, the odds are you don't have to adapt the water line, gas line or duct line.

At this point, you are half done with your water heater replacement, now you have to put everything back, but in reverse order.

Step 6. Connect water heater with plumbing

First check, what type of water line you can install. If it is the solid copper pipe, use it. Solder the pipe and copper fitting to the heater on one side and plumbing on the other. If you have to work with galvanized pipe, use a wrench and union to make a connection. The easiest way is using the flexible copper pipe.

The temperature and pressure relief valve or short TPR valve, as the safety element must be installed on the heater, and is provided / built-in by the manufacturer.

Step 7. Connect water heater to the gas line

Hook up the gas using a rigid (iron) pipe, usually called a black pipe, or flexible connection (check local code). Use pipe joint compound or Teflon tape for all male type threads. Take the gas "T" fitting with a capped nipple at the bottom and using a wrench tighten it to the pipe, and connect it to the gas valve on the heater.

The upper end of the nipple will be connected to the gas line and bottom to the drip leg, so it can collect sediments, dirt and moisture from either natural or propane gas.

Step 8. Check gas line for leaks

checking for gas leak using soap

Once done with the gas line, open the main gas valve and use soapy water and brush. Apply soapy water on all the connections and if the bubbles are coming out, you have a gas leak problem.

Solution for this problem is easy, you have to tighten the connection. If gas is still leaking, turn off the gas valve, dismantle all the fittings, clean it carefully especially treads, seal it, don't over tighten and run the test again.

Step 9. Install the flue pipe

Reusing the old vent pipe make sense as long as you didn't have any problem with the performance with the previous heater. If the size of the unit is the same and if the flue is not broken, no cracks, no changes in bends and diameter and no rust elements no need for a change.

Once you clean the flue from dust, residues, sediments and rust install it in the same order those marked segments, and with the same inclination. Don't forget to put screws back, to connect flue pipes together.

Step 10. Light the pilot flame

This is the last step in water heater replacement mini guide. Excited.
It wasn't that hard, right?

Turn the valve on and open the nearest hot water tap so air won't be trapped in the tank heater. When the water flows freely close the tap.

At the bottom of the gas heater, there is an access panel. Use piezo lighter and lit the pilot flame. The heater should start working now.

And you are all done with DIY gas water heater replacement.

(All pictures are courtesy of