Adding a "pre-boiler" to a Gaggia Classic

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#1: Post by Jochen »

Dear All,

Recently I bought a Gaggia Classic and enjoy it very much. I've read a lot about the thermal instability and ways to deal with it or to improve it. So today I started thinking about adding a second boiler in series as a "pre-boiler". I have an old Ascaso Arc Fun which I don't use. It has en small brass boiler. The Gaggia boiler and grouphead will be used as main boiler and the Ascaso boiler as pre-boiler. Is there anyone who has done this before, or knows someone who has done this before? I'd like to know your thoughts on this and whether it would be a good idea (pro's & cons) and things I may need to take into consideration.

Things I have thoughts about so far:
- I will need a new (adjustable) OPV and close the existing OPV on the Gaggia boiler. The new OPV will be placed before the first boiler, so only cold water will return to the tank.
- I will use the existing electrics of the Ascaso and will connect the two circuits via a relais so both boilers will be switched on by one button.
- I will use the Ascaso boiler including portafilter to increase thermal mass and water capacity.
- I will connect te pump to de Ascaso boiler.
- I will connect the Ascaso boiler to the Gaggia's via a hose connected to the Ascaso's PF and the Gaggia's OPV (and Gaggia boiler).
- The steam outlet on the Ascaso boiler will be closed.

One thing that I suspect to be a problem will be the unsynchronised heating cycles. Therefore controllability of the actual brewing temprature might be an issue. The Ascaso boiler has a thermostat at 100 Celsius and the Gaggia has one at 107 Celsius. The Ascaso boiler has a power of 900 W and the Gaggia 1300 W, I think.

It might not be the easiest way of dealing with the thermal instability, but I think it's an interesting one and I enjoy building my own projects, so it serves two purposes :D.

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#2: Post by TrlstanC »

I tried a very simple version of this with my gaggia, and the only real concern I could come up with was that the gaggia's pump wasn't rated for hot water. I guess the pump might cause it to wear out faster or something? But I never had any problems with it.

What I did was to just boil water in a kettle and pour that in to the Gaggia's reservoir. It's not a very elegant solution, but it did significantly reduce the temperature drop during a shot. It didn't do much for the stability of the temp shot to shot, that's mostly the fault of the thermostat, which has quite a wide band between open and close. A cheap pid kit can fix that though, and in my opinion made a much bigger improvement then preheating the water.

In fact, with a pid, the gaggia was fairly consistent shot to shot with just a little practice, and I found that the relatively huge intrashot temp swings actually worked very well for some coffees. I remember getting some excellent shots from Vivace's Dulce espresso and a lot of very good shots from Caffe Fresco's Ambrosia espresso. I assume both of them handled different temps very well, or maybe even improved with a temp change during the shot?

Jochen (original poster)

#3: Post by Jochen (original poster) »

I was thinking about connecting the pump to the Ascaso "pre" boiler. Therefore the pump would only pump cold water.

Adding a PID is another thing on my list. I have worked with Arduino's before and am thinking about doing an Arduino controlled Gaggia. A PID would be one of the things that I would add to the Arduino. I'm also thinking about making an app that can remotely switch on my machine or set a timer so it is ready to go in the morning or when I get home.

A pre-boiler might become a little obselete if I plan on doing an PID anyway, but I enjoy doing these kinds of projects and this is a fairly simple one I believe. An Arduino based PID will probably be a lot harder and take a lot more time so I don't see myself finishing that any time soon. The pre-boiler projects might only be a couple of hours work if I have the right parts.

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#4: Post by HB »

FYI, for those who are interested, Jochen has started the same discussion on CoffeeGeek here. Jochen, if you're looking for another site to discuss this topic, you should search the Gaggia Users Group. No doubt your question has been asked and answered multiple times there.
Dan Kehn

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#5: Post by pizzaman383 »

My brother and I have experimented with the Gaggia Classic and KA Proline boilers. After quite a bit of experimentation the configuration that works best for us turned out to be a PID-controlled J-boiler that feeds preheated water to the Gaggia Classic boiler that is also PID-controlled using a small-diameter thermo-well with a fast-responding thermocouple measuring the water temperature inside the boiler. It's got very consistent temperature control and fast recovery. It's pretty impressive for a low-cost, high results solution to the espresso game.
LMWDP #551
“Taste every shot before adding milk!”

Jochen (original poster)

#6: Post by Jochen (original poster) »

In my search for similar projects I came across yours. It's good the see that the concept has been proven to work.

I'm still having a bit of trouble with outlet on the pre boiler. My plan was to connect a teflon hose to the PF, but it's an M10 thread instead of the usual 3/4. I have searched a lot but haven't found a connecter yet. Now I'm thinking of making my own. It's unfortunate that the steam outlet is next to the water inlet. I'm worried that if I use the steam outlet, cold water won't have enough time inside the boiler to heat up.

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#7: Post by pizzaman383 »

My brother did a bunch of work sorting out connectors. Most of the thermoblock heaters are available with various different connectors. Send a PM to BigEric and ask what he used.
LMWDP #551
“Taste every shot before adding milk!”

Jochen (original poster)

#8: Post by Jochen (original poster) »

So, this week I've finally finished my pre-boiler project. What a difference! No more sour shots for me. So inter-shot stability has improved quite a bit. I don't no so much about intra-shot stability, since I never pull a second shot within 30 minutes. One thing I noticed is that the heating cycle of the Gaggia boiler has increased a lot. It went from about 2 minutes to about 4. I guess it's because there's another heater right next to it in a very small space.

I took a lot of puzzeling to fit the boiler inside the Gaggia casing without drilling any holes that would be visible from the outside, but I did it.

Unfortunately I had to get rid of the portafilter. The M10 thread on it broke off. I had made my own connecter to connect the 1/8 tube connecter to the M10 thread, but it was leaking a bit. So I had used quite a lot of teflon tape and tightened the connecter very hard, but then I tightened it too much and the soft messing broke off. Forntunately there's another hole inside the boiler which was exactly the right diameter to tap a 1/4 thread.

Next up is an Arduino based PID for the Gaggia boiler. If it works I'll install one on the pre-boiler as well.

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#9: Post by AZRich »

This is an interesting project. I recently picked up a used Gaggia Classic and have a pid attached. I think you will certainly want to add that to your project. I first ran some tests using the stock thermostat. On mine once up to temp initially, the heat would cycle on for only about 15 seconds, then not come on again for roughly 5 minutes! The deadband was more than 30F. The pid eliminates that big deadband. I see what you mean by tight fit inside the case - I imagine it gets hot in there with 2 boilers in a small space! Have you measured the brew pressure to see what effect the extra water path has on pump pressure once it get to the coffee? Also I'm not sure I understand your reference to a portafilter. Anyway I admire your effort. (hope you don't open that steam knob accidentally!)
regards, Rich
No adult supervision.

Jochen (original poster)

#10: Post by Jochen (original poster) »

I have measured brew pressure via a PF pressure gauge, but not pump pressure, so I don't know the pressure drop. I do get about 9 bars at the PF, that's all that matters right.