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Do You Have to Drain Your Water Heater to Replace the Gas Valve?

If you are noticing hotter than normal water in your home, or maybe the water is too cold, you could be having problems with your water heater, specifically with its gas valve. However, knowing where to start with replacing the gas valve can be a challenge.

When I started replacing mine I wondered if it is necessary to drain the water before replacing the gas valve.

Removing and replacing a gas valve requires you to completely drain the water heater, turn off the gas control valve, turn off the gas and water supply.

But that’s just the first step. Draining your water heater and replacing its gas valve can be rather complicated, but this step-by-step guide will help you understand not only how to replace your gas valve, but the cost of replacing it and why you should or shouldn’t do it.

How to test if a gas valve is bad

First of all, before you go about attempting to replace your gas valve, you need to check that the valve is for sure the problem. Sometimes your substantially fluctuating water temperatures can be caused by short cycling, which is when the water heater is not heating the whole time it is supposed to.

It’s important to check the pilot light and the thermocouple before deciding to replace the gas valve.

Rheem UV6379L UV6379L-Thermocouple

However, if you have checked the other parts on your water heater and know they are not the problem, then you can test your gas control valve to confirm that it is the part that is causing the inconsistent water temperatures. There are a few different ways to test if your gas valve has gone bad.

Lighting the pilot

Since the water heater controls the pilot light, you’ll want to follow the directions for lighting it on your water heater. (But don’t try to light it if you smell gas).

Pilot light of a water heater

If the pilot does not light at all when you press the button down, check the gas supply. If the gas is on, then check to make sure the pilot line or the orifice is not clogged up. If the pilot does not stay lit when you release the pilot button, then the thermocouple could be the problem.

If you replace the thermocouple, make sure it is properly installed with the tip of the probe in the pilot flame, the thermocouple screwed all the way on the control valve, and the line is not kinked up. If you the pilot will still not stay lit, then the gas valve is the problem.

Testing the thermostat

Sometimes water heater thermostats can malfunction, meaning the gas valve might need replacing. In order to test this, try turning the thermostat all the way down. If the gas burner stays on, then your gas valve needs replacing.

This could also work the other way. If your water heater tank is full of cold water your thermostat is turned up, the pilot is lit, and the burner doesn’t turn on, either the orifice is clogged, or the valve is bad. Before replacing the valve, make sure to check the orifice and burner supply tube for any congestion.

Technician checking the thermostat of a water heater

Other quick tests

There are a few other quick ways to know the gas valve needs to be replaced. This includes when the pilot button doesn’t pop up when you release it, the control knob won’t turn, or if the high limit shuts the gas valve off.

How to drain a water heater

If you’ve completed the different tests and found that the gas valve does indeed need replacing, the next step is to begin removing the gas valve. Removing and replacing a gas valve can be complicated, so make sure you know exactly what you’re doing, otherwise, you might want to look into hiring a plumber.

Nevertheless, if you are committed replacing the gas valve yourself, you’ll first need to turn off the gas valve, turn off the gas supply, and drain the water heater. That last part can be a bit tricky, so here is a guide to walk you through it:

Turn off the water supply

At the top of the water heater, you will find the water supply valve that needs to be turned off to stop the flow of cold water into the water heater tank.

Turn off the water heater

With a gas water heater, this means turning the thermostat to the “pilot” setting, which if you ran the tests in the above section, it should already be on this setting.

Attach a hose to the drain valve

Close to the bottom of the water heater tank is the drain valve. Once you locate it, attach a standard garden hose to it. Place the other end of the hose near some kind of drain or in a large bucket. Just be careful not to touch the burning hot water.

Turn on hot water tap

Turn on the hot water of a tap water faucet that’s near, and preferably above (on an upper floor), the water heater. This will help lighten the water pressure to help the tank train more quickly and efficiently.

Open the drain valve

Open the drain valve to let the water run from the tank, through the hose, and into the drain or bucket. If the water looks dirty, you can clean out the sediment build up in the tank by briefly turning the cold water supply on from time to time to stir up the remaining sediment. Do this until the water runs clear.

Drain valve of a water heater illustration

If the water looks dirty, you can clean out the sediment build up in the tank by briefly turning the cold water supply on from time to time to stir up the remaining sediment.

Replacing the gas valve

After you’ve drained the water heater tank, you can now finish removing the valve and replace it with a new one. This process can also be a bit challenging and a somewhat dangerous task, especially since you are dealing with gas.

If you don’t know for sure what you are doing, make sure to seek out help. Also, make sure to use factory authorized replacement parts only, do not use a pipe wrench to grip the body, and do not apply to much force, in order to avoid damaging the element.

Disconnect the wires

There will be multiple wires and parts that you will have to disconnect from the gas valve. These include the gas flex hose, thermocouple, pilot tube, main tube, the piezo igniter, and thermal switches. You can disconnect them with a screwdriver or pliers.

Unscrew the valve

Remove the valve by tightly screwing the correct size of threaded pipe into the inlet of the gas control valve and then turning the valve counterclockwise with the pipe. You want to avoid using a large pipe wrench or anything that could put pressure on the valve because it could cause damage.

Technician unscrewing the thermostat valve on the water heater, illustration

Prep the new valve

Get the new gas valve ready by wrapping Yellow Teflon tape around the connection threads that go straight into the heater to avoid any leaks.

Screw in the new valve

Screw in the new valve using the threaded pipe. Make sure it is screwed in well (but do not overtighten) and the valve is straight, parallel with the water heater.

A.O. Smith by Honeywell Gas Control Valve 100262939 2" Cavity Natural Thermostat Compatible with A.O. Smith, State, American, Whirlpool, and Craftmaster Brand Water Heaters

Reattach the connections

Reconnect the piezo igniter, thermocouple, and all other connections you detached from the valve in the beginning. Pay attention to thread direction and be careful not to damage the delicate pieces. Also, reconnect the gas pipe or gas flex hose.

Refill the tank

Close the drain valve that you had opened to drain the tank and turn the cold water supply back on to allow the drain to fill up. Turn the hot water tap on again to release pressure. You can also turn the gas supply back on at this point.

Test for gas leaks

Apply a foamy soap and water mixture to all the gas connections. If there are any bubbles then there is a leak. Try tightening the connections or replace them with a new gas line.

Light up the heater

Get the water heater going by using the lighting instructions found on the heater label or the user guide to start the water heater back up.

Is it worth replacing the gas valve?

While removing and replacing the gas valve is a viable solution to fixing your water heater, many plumbers and technicians typically recommend replacing the whole water heater if the gas valve is bad. Most water heater gas valves average between $100 and $200, but if you are not comfortable installing a new gas valve yourself, then it will cost even more to hire someone to do it for you. Hiring a professional can cost up to $500.

If your water heater is close to or past its expected lifespan (10-15 years), then it’s usually not worth replacing the valve

If your water heater is close to or past its expected lifespan (10-15 years), then it’s usually not worth replacing the valve because of all these extra costs, and you will most likely have to replace your entire water heater (which costs anywhere between $1,000 and $3,000) soon anyway.

The process of replacing a gas valve is also complicated and can be prone to causing damage to other parts, especially if you are unsure of what you are doing. That’s why it is recommended, but not required, to replace the entire water heater when your gas valve goes bad.

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