Since I've got the S1 Vivaldi, I found myself using the hot water tap a lot more than what I was expecting (can provide as much as 1L), even if I understand that a $2000 machine is not to be used as a $10 kettle, that I will get more scale as more water is going through the steam boiler, etc. Instant hot water is practical and this is simply hard to ignore.

The only issue I have is that the process is very inefficient: ~110°C water coming out as some 100°C hot water along with a lot of steam. The water is also too hot for our main use: green tea. We cool it off to 75-80°C (~175°F) by moving it through two different vessels before infusion. Wasted electricity to heat water, wasted electricity for the air-conditioner to cool down the excess heat.

I've looked at the setup of the GS3 mixing valve but I can't easily figure out the exact water flow (see this thread, for pictures).

From page 6 of the GS3 parts catalog

I'm considering the addition of a hot water mixing valve to my Vivaldi to cool water to a more reasonable / practical temperature. The machine is plumbed-in and uses a solenoid valve for hot water. It uses plastic tubing, which seems ideal to do the mod (provided I can get the correct parts and fittings).

Am I correct assuming this is a working setup?


I assume:
- A check valve is needed on the cool water side to avoid water from the steam boiler to flow back to mains? (not really possible as mains is at 2.5 bar and steam boiler at 1.35 max) Useful? Only as an additional safety?
- A check valve is needed between the steam boiler and the mixing valve, else water would flow from the mains (2.5 bar) to the steam boiler (0-1.35 bar), making an instant mess.
- I can find a spot to localize the additional parts inside the S1, ideally with quick access to the mixing valve (behind drip dray for example).

Questions:
- How do I make sure hot water at 1.35 bar stills comes out through the mixing valve while the incoming cool water is at 2.5 bar? I'm missing something....
- Do I need a thermostatic mixing valve, as the steam boiler pressure can vary, to keep a constant final water temperature (cool water pressure is regulated).
- Where can I find such a mixing valve?
- Any idea where I could procure the correct parts?: connector to the S1 plastic tubing (out of steam boiler, back to hot water solenoid), Y between cool water mains and F-o-T pump inlet, inter-parts connections between the additional parts, check valves, Y, etc.
- Any worries to keep in mind to avoid a big mess (I'm already protected by an automatic mains shut-off in case of water leaks) or equipment damage?

I agree the GS/3 parts diagram isn't easy to follow, much easier if you look at the GB/5 parts diagram (though it uses slightly different parts). Your schematic looks correct aside from LM having the pump before the tee that goes to the mixing valve, along with a software setting for selecting whether to have the pump running or only mains pressure when tapping hot water. I will be doing this mod to my Linea as part of a major upgrade to GS/3 spec (including a GS/3 brainbox).

Bob_McBob wrote:Personally I'd be inclined to save myself a lot of time and effort and just get a Zojirushi hot water dispenser.

Ditto. We have a GS/3, but find the Zojirushi more convenient for tea and other hot water needs.

Cimbali uses what they call an economizer to mix boiler water with cold water. It is adjustable for temp and seems to be a simpler design. It may be prove more difficult to retrofit, however.

Just as a heads-up, my old Monster Briccoletta was modified to include this feature - and it was this modification that failed and caused the machine to blow up.

malachi wrote:Just as a heads-up, my old Monster Briccoletta was modified to include this feature - and it was this modification that failed and caused the machine to blow up.

Chris, what happened? Faulty design on your part? Faulty part? Are you saying I should seriously abandon the whole idea (high risk), or only that I should make sure I do things properly?

I usually just nuke my hot water, but if I really want to use my Vivaldi, I use the steam to heat up the water. It really works pretty darn fast.

Mayhem wrote:I agree the GS/3 parts diagram isn't easy to follow, much easier if you look at the GB/5 parts diagram (though it uses slightly different parts). Your schematic looks correct aside from LM having the pump before the tee that goes to the mixing valve, along with a software setting for selecting whether to have the pump running or only mains pressure when tapping hot water. I will be doing this mod to my Linea as part of a major upgrade to GS/3 spec (including a GS/3 brainbox).

I found a GB/5 mixing valve at espresso parts.com ($21).
The GB/5 parts catalog is here (PDF).

A "Pre-heating mix valve" is shown on page 31. It is a metal block with three water ports on one side and a thermostatic valve assembly on one end. It is not what I'm looking for: it seems like a device to mix overheated water from the steam boiler HX (page 37) with cold water (page 37, water mains inlet page 35) before it goes in the coffee boiler (page 33).

The part listed by espresso parts is shown on page 35 (part 13).

It (part 13) gets cold water from a tee (bottom) on the steam boiler refill line, and outputs (through a check valve, part 12) to another tee (part 10), which mixes this regulated amount of cold water at pump pressure (9 bar from outside pump) with water(/steam?) coming from the steam boiler (from right of part 10, again through a check valve (page 37). The third outlet of the tee (part 10) is then going directly to the hot water solenoid (part 8 ), before ending in the hot water tap.

So, going back to my original drawing, my "mixing valve" is really only a tee and I need to add a regulated valve between cold water tee and the cold water check valve. I've got the rest correctly set up:


Thinking again about the pressure differential issue, I have:
1. cold water from mains, regulated at ~2.5 bar (35 psi)
2. hot water from steam boiler, at 1-1.35 bar (1.35 at set temp, 1 bar when steam valve is opened)
3. hot water tap at 0 bar
It then seems like a "water mix valve", set at the correct opening, will deliver just enough cold water to the mixing tee to cool down the steam boiler water (~110°C to 75-100°C).

Now that I understand the setup in theory, where do I start with to actually do something?
- Where can I find in parts catalog the type/thread pitch/size of fittings used? How do I know different parts I would order online will fit together? All parts catalog I've looked at don't say a word on this.
- If I want to put everything together using plastic (teflon?) tubing, what kind of fittings will be required?
- Can I simply assume parts/fittings from LaSpaziale could fit with parts from LaMarzocco (thread pitch, size)? (Wouldn't that be great!)
- Where can I get all these parts? Any repair shop? (Chris Coffee for LS? Espresso parts for LM?) Do they usually carry every part? (My order would be a mix of heteroclite parts).
- What is special about the mixing valve? Is it pressure regulated? If I buy this one made for a LM under 9 bar of pressure, would I need to be really lucky for it to fit under 2.5 bar with different water tubing sizes?