I've got a Gaggia TE, heat exchange, machine that's plumbed in. The steam coming out of the boiler recently started to smell strange: a bit musty and maybe somewhat sour. (Same for the water coming out of the hotwater spout.) I drained the boiler, flushed it out a couple times, which cleared it for a bit. But it comes back pretty quickly. I think it might have started not long after doing a backflush. I'm wondering if there is some coffee from the grouphead that is leaking back into the boiler, perhaps through a hole in the heat exchanger? Any ideas?

Thanks.

Sometimes comes from milk getting sucked back into the steam wand. I always try to make sure that I expel some steam after steaming milk so this doesn't happen.

Thanks Hal. I'm pretty careful with clearing the wand. Would this account for the bad water back in the boiler that was coming out of the hot water spout?

Absolutely. The same procedure for descaling will freshen the steam boiler.

I had a boiler on a Faema get contaminated with milk and go skunky. Descale acid did not do much. I had to use backflush detergent (JoGlo) to get the rancid film out of the boiler. Same thing with coffee oils. I figured I would just drop the groups into the descale solution with the boiler. That would clean them up. Did not do a thing. The acid had no effect on the greasy, oily buildup but a bit of detergent cleaned it right up.

As Dave accurately reports, descaling helped, but did not clear up the whole problem. I ran some dishwasher detergent through the boiler and wand then rinsed several times. So far so good. Thanks.

Here's what can happen inside your boiler:



If your steam continues to smell, you might have to pull out the boiler and clean it.