The city shut off water for a couple hours overnight without notice. When I tried the faucet in the morning it ran dry. I also noticed that a pump in front of my hot water heater started making noise, almost like water is constantly rushing through. The pump is hot to the touch. It's never been audible before. Turning the pump off overnight (wall switch on the left in the photo) and back on doesn't change much.

I believe some air has gotten into the pump. How do I bleed the air out? Here is a picture of the pump on the cold water line leading into the heater.

The hot water heater is on the 3rd floor. This is in a relatively new construction home, built in the last 5 years. The pump is at the top of the picture.

hot water heater pump

  • would vent the whole system, open all faucets on cold water first till it comes out. Now do the same on the hot water pipes, also vent the boiler to let the air out
    – Traveler
    Feb 10, 2023 at 7:25

1 Answer 1


Unless there is a vent somewhere not in this picture, it looks like you have a system that was poorly designed - there does not appear to be a way to vent it properly built in, and the pump is positioned where air will be trapped in it.

You can flush the pipes to your heart's content, and the recirculation pipe will be sitting there full of air because it's not in the path between the water supply and the faucets, so the only way it's going to flow is if the pump can run, while the pump can't run due to trapped air.

Check the far end of the recirculation loop for an air vent, or a fitting you can unscrew to vent air. Or, given this is on the third floor, check the highest point in the recirculation loop. Have a bucket or tub handy if you need to unscrew a fitting, and try to get the air out without unscrewing it all the way so it's easier to tighten it without fighting a flood.

  • Just a couple of thoughts: Usually re-circ pumps have a vent on the side which looks like a large screw, about 3/4" , it's used to vent the pump...not sure if yours does but my Grundfouse pumps do. Also, they don't like to run with no pressure, even if full of water. Mine gets hot if I have to turn off the water and forget to turn off the pump. If running for a long time w/no pressure, the impeller may have melted. Like Ruskies said, try purging by opening up everything, then turn on the pump, if it works, great, if not, probably time for a new pump. Feb 10, 2023 at 15:57

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