The Dirty Portafilter

My corner of the Internet, mostly espresso related but occasionally life will interfere.

Saturday, April 08, 2006

Diagnosing a Broken Heat Exchanger

The machine has no auto-fill, I removed it. My original thought was that the manuel boiler fill valve was bad and water was flowing to both the group and boiler.

I removed the boiler supply line from the valve, put my finger over the tube to stop the backflow, and turned on a group. I had water running out of both the group and the boiler side of the valve. So I drained the boiler and removed the valve. That was the one part I did not rebuild. The bolt holding the works together did not want to let go. I put it in a padded vice and persuaded the bolt to let go. It was green and crusty; the seals were compacted and hard. I de-scaled the valve (looks like new) and replaced the seals.

I then repeated the above test with an empty boiler. Water came out of the group but not the fill valve so it is now good. A moment later water started coming out of the boiler line that I had not hooked back to the valve. That should not happen. There is only one way to fill the boiler and that is via the boiler fill valve which I had disconnected. I also never got more than a dribble out of either group.

I reconnected the boiler fill line to the valve. I filled the boiler about half way, engaged one group. I got a small dribble of water out of the group but the water level in the boiler sight glass was increasing. I engaged the other group, small dribble of water and the boiler level rose again. Having eliminated the boiler fill valve, and there is no other connection to the boiler, the water must be coming from one or both of the HX tubes, hence my supposition.

The squirt of water from the right group may have been completely coincidental. I had disconnected both group supply lines at different occasions. As you point out, both groups are supplied by a common line. Once the boiler cools, osmosis would dictate that the remaining pressure between each group be equal because it is a sealed system. My observation may be, and probably is, purely coincidental.

One last test, I disconnected the group water supply line. I then set my air compressor regulator to somewhere around 50psi. With both groups closed I should be able to generate some pressure in the brew pressure gauge, which is downstream. After a moment of blowing air into the line, I did get a small rise from the brew pressure gauge. Then suddenly the boiler pressure gauge spiked to max (15psi). The only way the boiler could have pressurized is if one of both of the HX tubes is cracked. The pressure I was pumping into the brew groups bled into the boiler.

I now have one HX fitting cap and one HX supply line plug. I will cap the left group (easiest to get to) and left group supply line. Put some water into the boiler and engage the right group. If the group is good, then I will get normal water flow from the group and no increase in boiler water level. If I do get water into the boiler, I will reverse the fittings and cap off the right group. When I then engage the left group, I should get normal water flow and no boiler increase. If I do, then both HX’s are blown and the boiler is trash. If not, I will leave the bad HX capped and use the one good group until I find a replacement boiler.


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