How to Stop a Vapor Lock in Plumbing

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A vapor lock is something you associate more with gasoline engine fuel lines than you do with plumbing pipes, but it does happen, and it can reduce water flow to a trickle. A bubble, which may have been introduced by your well pump or by plumbers working on the municipal water lines, lodges in one of the water pipes — usually near an elbow — and creates a constriction or obstructs water flow altogether.


A proper remedy is to turn on all your faucets at once. That usually works, but if you're concerned about wasting that much water, you can also try backflushing the faucet that has the most noticeable flow problem. Backflushing is a way to get sediment and debris out of the pipes, and it can also remove air.

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Using the Whole House Method

Gravity is your friend when trying to bust an airlock, and you can use it to create enough negative pressure in the pipes to suck the air right out. That's why you should start opening faucets in the lowest part of the house first. Here's how:


  1. Turn both the hot and cold faucets in the lowest part of the house about 1/8 of the way.
  2. Then, work your way upstairs opening the hot and cold on all faucets, including those in the kitchen, the laundry room, and the bathroom, and be sure to open the tub and shower faucets as well as the sink.
  3. Leave the faucets open for about two minutes, then start closing them, again starting from the lowest floor and working your way up. This is a double-check. Air that didn't get sucked out through the lower faucets should rise to the higher ones and flow out there.
  4. When you're done, flush all the toilets at least once.
  5. If your refrigerator has a water dispenser, put a cup under it and fill the cup with water to guarantee no air remains in the system.


Shut Off the Main Water Supply

Should the whole house method not work, there's another trick that involves turning off the water to the house. As long as you know where the main shutoff valve is, you can use this method:

  1. Shut off the main water supply.
  2. Open all the faucets in the house including the ones in the tubs and showers, starting with the one closest to the shutoff valve. Open them just enough to allow air to escape. Flush all the water from the toilet valves (you don't have to empty the tanks). You want every faucet to be open, so that means turning on your dishwasher, washing machine and outdoor spigots.
  3. Open the main valve and let water run through all the faucets until you see a normal flow rate from every one. At that point, start turning off the faucets in whatever order is most convenient.


Backflushing to Remove Vapor Lock

If a particular faucet has lower than normal flow, the problem could be due to air or sediment, and backflushing should take care of both. Here's how to properly backflush:

  1. If the flow rate is low in the hot water pipe, and the faucet has a single handle, turn off the hot water valve at the water heater.
  2. Put a dime in the aerator to block the spout of the faucet you're backflushing.
  3. Open a hot water faucet somewhere else in the house and turn on the hot and the cold valves of the original one.The backflush of cold water should force the air backward and out of the second faucet.
  4. Let the water run for two to five minutes, then check the flow at the original faucet and repeat if necessary.


The procedure is the same for a vapor lock in the cold water line, but you'll need to shut off the water in the whole house and use a hose connected to a neighbor's water supply.



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