Hi all, another good one!

A little background first - I work in an office that only had a pod machine. About half a year ago I had a bunch of BDB parts lying around from 3 different coloured machines, so I decided to make a machine out of them. I called it the FrankenBrev. I've had it in the office since a week after I got it running and tested. Worked beautifully the whole time at around 8 - 15 coffees a day for the 2-3 days/week I was in. I recently decided to remove it and give it to my sister as an upgrade from her old sunbeam.

As soon as I set it up at her place, the gurgling began. Couldn't get past 7 bar while pulling a shot and they came out nothing like they used to - very runny. I gave her the grinder I had at work also, so the settings are all the same. I roast beans for myself and the family, so they're all the same too. Never happened before, so I took it back home to work on. The orings are only 6 months old, but I replaced & lubed them again anyway to be safe and checked all the hoses. The pump is also new. The OPV isn't but it is working like it should and holds at around 9.5bar with a blind filter. No visible or audible signs of leaks.

For poops and giggles I thought maybe the air leak was from the coffee boiler probe seals. The probes are stuck in there, so I replaced the boiler with a spare I had with all new seals. No luck unfortunately.

I decided to put a light behind the tubes to watch the water flow while pulling a shot. I noticed that pockets of air were flowing into the coffee boiler from the HX outlet. I don't see any flowing back into the pump after the shot or any air pockets in the HX inlet hose once it's cool. The HX inlet hose seems to stay full with no air pockets, aside from a tiny bubble or 2 which is negligible. This tells me the one-way valve is happy and working.

Could I be one of the few lucky blokes with a leaky HX pipe in the steam boiler, or is there anything else that can still be tested? I've done 3 steam boiler replacements in the past couple of weeks and am hoping this isn't another.

Thanks all, sorry to rack your brains but these weird and rare issues seem to have a thing for me

You can test that by draining the steam boiler then connect a power lead to the coffee pump and then turn it on and see whether any water appears inside the steam boiler.

That is genius, I'll give that a shot. Thanks mate! I feel like an idiot for not thinking of that.

EDIT: No luck with that. If there is a breach in the HX pipe, it must be small enough to not let water drip out but big enough to allow steam pressure to get in. Replaced the pump with a brand new one as well just to rule that out, no change.

Maz wrote:If there is a breach in the HX pipe, it must be small enough to not let water drip out but big enough to allow steam pressure to get in.

Not likely above 0 Celsius.

Any idea what else it could be? The air pockets in the HX outlet hose are much more frequent once the steam boiler is at temp. If I let it sit for a minute or so the hose fills with air as the water gets pushed into the boiler.

If there's air in the system, it's getting in somewhere before the pump. Downstream of the pump outlet nothing is at less than atmospheric pressure, fluids would try to leak out, not in.
I don't know how effective the vacuum-breaker valve is in your specific machine, but even the steam boiler should have no "air" (gaseous nitrogen with a small amount of other gasses) inside. The gaseous water (steam) will displace pretty much all of it as it comes to a boil, before the vacuum breaker is closed.

It's very possible there's steam in the brew circuit. As the heat exchange tube sits there taking on heat the water inside is raised well above boiling temp. If there's any leakage in the system, the water will be able to expand, become steam and quickly displace whatever's in the brew circuit. It is not likely for the steam circuit which sits at maybe 1.4 Bar to be forcing air, steam or anything into the brew circuit that sits at whatever pressure opens the expansion valve, probably 11 or 12 bar..

I can't see or hear what you're talking about, but I think I can visualize it. Can you use a tube as a stethoscope to determine exactly where the gurgling is? Is it actually a problem or just a curiosity? More importantly, is the machine working?

That's pretty interesting, in that case it could be something as simple as the seal that the water tank pushes into that might be letting some air in. That would make a lot more sense now that I think of it as there is often some water there when I pull the tank out.

The gurgling is coming from the brew boiler once the air pockets from the HX outlet enter into it, and even more so in the first 4 or so seconds after pressing the brew button. The machine works for the most part, however due to the air, pre-infusion is a little out of whack, as is the overall brew pressure. On a 22g dose the pressure would previously move nicely to around 3 bar by the end of pre-infusion before settling on around 8.5bar which was perfect for me during full extraction. Now, the pressure barely moves during pre-infusion and struggles to reach ~7bar while making a very runny shot. A large amount of water is forced out in the first 2secs of PI, followed by about 2 secs of just air, then a small trickle before the pump goes to max. The pump is definitely working during PI.

I went through the error codes again and found the coffee NTC had gone over temp a handful of times as well as a few coffee flow error counts, I'm guessing due to the air not allowing the boiler to fill to it's correct capacity. I have my temp set at 94, and I watch it hesitate at the 92 mark, dropping back to 91, then holding 92 again for longer than it should before settling on 94. I found that using the water tap when that temperature hesitation happens releases some pressure out the spigot and stabilises the temperature.

Really appreciate your insight, I'm not the sharpest tool in the shed but that kind of break down fascinates me.

Maz wrote:That's pretty interesting, in that case it could be something as simple as the seal that the water tank pushes into that might be letting some air in. That would make a lot more sense now that I think of it as there is often some water there when I pull the tank out.

I had similar thing on my Spaziale Dream - the pump was "air-locking" & wouldn't stay primed. Replaced & lubed the o rings on the check valve where the reservoir tank connects & the problem was solved. air was getting sucked in by the pump due to a leaky seal at the old & dried out o rings

Glad you fixed it. I've had the same issue before and did just that, but this time it's different. Just replaced the seal with a spare so there's no more water leaking when I take the tank out, but I'm still getting those air bubbles after the HX outlet. Triple checked everything before the pump and can't find anything.

Are you sure there are no air boubbles in the tube from the opv to the hx input. I've had similar problems caused by a worn o ring in the opv bypass allowing air into the bypass tube.