4 posts / 0 new
Last post
Draining an expansion tank

I have a gas boiler that continuously leaks from an overflow pipe. The expansion tank is a long green steel tank hanging from the floor joints. I believe the issue with the leak is that the expansion tank is full with water and no longer has the proper air to water ratio. We tried draining the water from the expansion tank but a constant flow of water from the boiler automatically refills the tank. I believe we need to drain the tank, and re-equalize the air level as well. How do I do this without the expansion tank automatically refilling? There is a valve at the inflow pipe of the tank and a special opener that I found. Is this involved in the tank drain?

Re: Draining an expansion tank

Yes, the procedure for "recharging the expansion tank" is to temporarily shut off the boiler switch, and close the valve on the pipe leading to the expansion tank.

There is usually a length of garden hose conected to the ET; if not attach one & point it out the door, or into the floor drain.

There is often a small six-sided fitting on the tank valve that takes the garden hose that is designed to allow some air into the top of the "waterlogged" ET; this can be loosened or removed temporarily.

Open the tank valve to drain the tank after the garden hose has been placed into a floor drain, or outside, or into a large bucket.

Drain ALL THE WATER from the ET; if you don't drain ALL THE WATER from the ET the tank will not re-charge properly with air.

Once all the water is out, replace the small six-sided fitting on the tank drain valve, close the valve handle, remove the hose, and open the shutoff valve that leads to the ET to allow water back into the drained ET (you will hear water running).

When the water stops running, check the boiler gauge, you should have 10-12 psi on the pressure gauge.

Turn the boiler switch back on.

If you still have trouble after this recharging procedure, there's a possibility that the pressure reducing valve is faulty, or some other problem exists.

Please post back with your progress report.

Re: Draining an expansion tank

If you have a site glass on the tank with rubber gaskets on the glass or valves -they might be dried out and leaking which allows air to escape and flood the tank.

Re: Draining an expansion tank

Thank you very much for the advise - the leaking has stopped!!

Although I noticed that the psi did not change once the ET was recharged. The before and after reading was about 26. But I also noticed that the temp (on the same gauge) wasn't registering at all. Think I just need to replace the gauge, or could there be another cause for both the temp and psi to be out of whack?

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.