Air vent atop expansion tank is bad. Can I just shut off the water supply and replace it without water (in the pipes) shooting all over?

Hi Rick

If the expansion tank doesn't have an isolation valve (shut off valve) then the answer will depend on whether you can isolate the feed and return on the boiler system. First, shut off the water to the boiler. Then, if there are shut off valves on both the feed and the return, you want to shut these valves and then release some pressure through a boiler drain on the boiler so you can unspin the vent and replace it. Here, just before you screw the new air vent in you want to start to refill/re-pressurize the system until just a little bit of water comes out the vent hole...now you can spin the new vent into place. If there are no isolation valves, you can try to depressurize the system by draining off some water from a boiler drain, but be clear that water will most likely flow from the vent hole with some force. In this case, it may be best to drain water from the system until you can safely replace the vent. Of course, you will need to re-pressurize the system and bleed all air from the system after you do this....takes time, but if the boiler was piped properly, it shouldn't take too long!

Finally, you can also try putting some Teflon tape on the threads of the vent cap and screw the cap on tight...should stop the water from flowing and then, when you have another issue with the boiler, you can deal with the vent at that time...boiler will be fine without it for awhile...;)

Back to you...

Mark