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Gas Furnace or Boiler


Can you tell me how I drain the expansion tank (hot water systems)? I have a spigot on the bottom of the tank. What has to be done after it is drained?



PLEASE NOTE: water in a hot water system can be scalding hot. You need to be very careful working around your hot water system to keep yourself from being burned. If you are un-sure what you are doing, you should contact a trained professional.

Newer hot water systems typically have a diaphragm-type expansion tank, which is sealed, so it's not necessary to drain it. However, from time to time, these types of tanks need the air inside them pressured up. Older hot water systems typically have conventional expansion tanks that should be flushed out annually. You can recognize a conventional expansion tank because they will have two valves around them: a shutoff valve going to the furnace; and a drain valve on the bottom of the tank.

Here is the procedure for draining a conventional type expansion tank. First, close the shutoff valve that goes to the furnace. Position a bucket under the drain valve on the bottom of the tank. If you cannot position a bucket underneath the drain, then you can attach a garden hose to the drain, and run the other end of the hose to a bucket. Once the bucket is in place, then open the drain valve. The water should flow out, but if it doesn't, it may be necessary to use a wrench to open the vacuum-breaker plug (not all tanks have this plug) on the drain valve. After the tank has been drained, close the drain valve and vacuum-breaker plug; then re-open the shutoff valve going to the furnace.

Once again, if you have any concerns about doing this procedure safely, you should contact a professional heating contractor.

Hope this is helpful.


Gas Furnace or Boiler