Air in Hot Water Lines? (DO THIS)

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One of the most annoyingly common issues with plumbing is air in the hot water lines. This can be noisy and interrupt your daily tasks. Thankfully, it is a problem that is not only easily identified, but easily solved.

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Signs of Air in Hot Water Lines

There are a couple telltale signs that you have air in the hot water lines. In the event you are old enough to remember (or have an older house with) steam registers, you will be quite familiar with the famous pinging noise caused by air in the pipes.

Another common sign is when water sputters out of the faucet instead of flowing. Similarly, the flow may be irregular and the flow might even cause your pipes to vibrate at lower pressures.

If water coming out of a tap appears cloudy or milky, it may be another issue but one that’s usually completely safe.

What Causes Air in Water Lines?

The answer to this is rather complicated, as different systems can have very different issues. The potential causes of air in both hot and cold lines will require a different form of treatment than when you have air in the hot water supply only.

Gravity-Fed and Other Municipal Water

While these systems function differently, the causes are the same. Most commonly, air will become trapped when the water supply is cut off for maintenance. Simply running your taps for a while can solve this issue.

Well-Fed Water

There are three potential causes of air in your hot water lines. A faulty check valve can be potentially serious, as it permits contaminant into the water supply. If you suspect the check valve, you should get it diagnosed and replaced immediately.

Methane gas is another contributor and, while it’s flammable, this gas is natural and generally harmless to the water supply. A third possibility is that the feed line isn’t protruding deep enough into the well water, allowing air to enter the line. This last possibility is most common during droughts when the water table is lower than usual.

Air in Hot Water Pipes Only

When the issue appears to be coming from the hot water pipes only, it’s an indication that you have air in your water heater. When the heater hasn’t been purged for a while, air and sediment can build up. This is especially true of well-fed systems, and the trapped air will often replenish over a couple hours.

How to Get Air out of Hot Water Lines

cleaning water heater

The best way to get rid of unwanted air in your hot water supply is to purge the tank. You should do this annually, and at least twice per year if you draw your water supply from a well. Purging air from your tank is a slightly different process than a regular purge and requires a few special considerations to ensure you aren’t replacing air with more air during the purge.

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  1. Shut off the power. For gas heaters, this means turning the switch near the bottom of your tank to close the gas feed and turn off the pilot light. Electric tanks can be shut off at the circuit breaker.
  2. Leave the cold water feed on and do not open any hot water taps in the house to avoid pulling air into the tank during the purge.
  3. For safety, let the tank cool for 30 minutes to an hour.
  4. Locate the drain tap at the bottom of your tank. And lay some plastic or tarp under it to avoid getting water on the floor.
  5. Attach a hose to the line and run it to your basement’s sewer. You will not want to drain directly to a bucket when purging trapped air, as frequently closing the tap can exacerbate the problem.
  6. Open the drain valve and empty the tank.
  7. The cold water will continue to fill the tank as you drain, forcing sediment and trapped air out. You can check the sediment levels by sticking the hose in a bucket as it drains and then letting the bucket sit for a few minutes.
  8. When the water runs clear (or no sediment appears at the bottom of the bucket after several minutes of sitting), the tank is drained.
  9. Cloise the drain valve and allow the tank to fill.
  10. Once the tank is full, restore power and relight the pilot, if using gas.

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  1. When you turn the hot water on the faucet it spits and like hammer’s and the water is hot you can’t just put your hands onder it and stem is coming out as well I’ve turned the thermostat as low as it will go and have even replaced it with a new hot water heater and still doing the same thing please help me if you can

  2. I’ve got the same problem. I believe it is the minerals in the water reacting with the anode. I’ve tried both aluminum and magnesium anodes; both gas “air” (gas) in hot water at taps. To trouble shoot this problem, you can replace the anode with a simple plug temporarily. If the issue goes away, you know that it is the anode.

    I am looking for a vent that I can install to auto purge the gas.

  3. Thank you for advise my hot water was milky and that’s what it was air in the water heater purging worked well , easy fix thanks again

  4. I live in an apartment complex. After the city made repairs at a neighboring complex, ours started to have water pressure issues. Our complex says it’s air in the pipes and it will work itself out. It’s been 11 days. Surely if it was going to work itself out, it would have by now, right? Does our maintenance team need to follow your 10 steps for each apartment?

  5. I just moved into house and the owner put a new hot water heater in but there is knocking coming from water heater once from turning on bathtub water and when washer was on is there something I can do to stop the noise

  6. I just had an element replaced in my water heater, now I’ve got air in my cold water lines so bad the toilets hammer when flushed…what is going on? How do I fix it? My plumber just brushed me off.

  7. We just installed a new water heater and the water is coming out good in the kitchen and shower but not in the bathroom sinks. It’s just a dribble. What to do ?

    • Is the outlet valve on the water heater opened all the way? Only the hot water is a dribble in the bathroom sinks or hot & cold? How is the tub or shower pressure?


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