# Gaggia Classic - main functional components and water flow



## MrShades (Jul 29, 2009)

I (quite quickly) produced this diagram of the main functional components of the Gaggia Classic, enabling you to see what's where and where the water flows.

Describing what you can see, and following the water through the system...

Starting with the water in the water tank - pipe in the tank feeds water to the pump. This pumps water (at some pressure >15bar) to the OPV. The OPV is set to bleed off "over pressure" water back to the tank (and it's this valve that is adjusted to allow the cutoff to be changed to 9 bar). Cold water at circa 9bar (on an OPV modded machine) enters the boiler (at the bottom of the boiler, remembering that hot water rises!).

There is a vertical pipe inside the boiler, which the brew water exits through - and this is a few centimeters long, allowing it to be within much hotter water (ie when the cold water is pumped in, as this stays closer to the bottom of the tank, hotter water can exit via this pipe - in theory, though when water is forced in at 9bar there's some considerable disturbance of the water in the boiler that'll result in the water being mixed).

When the brew switch is on, the Solenoid valve engages - that shuts the exhaust valve and allows water to flow from the boiler to the group / shower head. The 'click' when brewing is the solenoid valve actuating. When you turn the brew switch off, the solenoid valve deactuates, returning to its natural position - which allows water from the group / showerhead (and portafilter / puck) to exit via the Exhaust pipe - and in this state the water flow from the boiler is blocked (so brew water from the puck cannot get back into the boiler).

The temperature of the brew water is controlled (very roughly) by the brew stat (allowing the heating elements to turn on/off) shown in the side of the boiler.

When steam is required, the steam switch is thrown and the heating elements then turn on until the steam stat decides that it's hot enough. The steam stat is in the top of the boiler.

To produce steam at this point, it's a simple case of turning the steam valve - with steam being produced via the steam wand.

Anyway, that's the main parts of the process and the main components within the Classic - and hopefully allows more people to realise what's going on "under the hood" and diagnose faults themselves. You can certainly see why the solenoid valve is a key component, and why (when they stick or block) no water appears from the group (and usually the OPV kicks in and all water is simply pumped back to the tank).

Hope it helps...


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## charris (Feb 17, 2014)

I guess this is a sticky. Glenn?


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## TheEspressoNistic (Nov 11, 2014)

Nice...

Can't really find someone as good as OP right here to demonstrate internal mastery... in a simple yet comprehensive way....


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## peterj (Dec 23, 2014)

This so clearly shows what some hours of looking into the top of my Classic has failed to tell me







Thank you.


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## Psticks (Dec 23, 2017)

Excellent explanation, gave me a eureka moment, 😀👍🙏


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## MrShades (Jul 29, 2009)

This is from so long ago that I'd forgotten all about - Glad it's helping still!


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## Muratozt (Mar 27, 2021)

Hi, I have water drops from brewhead while steaming. This happens usually after steam light turns on. Do you know what could be the reason? Does it show a damaged solenoid valve not closing properly against increased pressure in the boiler? (my machine 2 months old). Or is it totally normal? (Maybe it was always like this and I didn't realise). I guess solenoid valve closes the connection between boiler and brewhead during steaming, but not sure. If so, these water drops might show a malfunction right?

My steaming power looks OK however I would like to know if it is negatively effected by these drops and if there is anything to do about it.

Btw descaling with a Gaggia descaler didn't change anything.

Thanks in advance,


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## Nightrider_1uk (Apr 26, 2020)

My guess would be crap in the 3 way valve, All Gaggis's do it to a certain degree, mine certainly does, but i'm not worried about, Another issue you could have which is common on Gaggia's is that the steam wand leaks, again i'm not too bothered by it and at some point i'll strip it does and clean it all properly, But i'm too busy using it.

I'm sure somebody more knowledgeable will tell you if its really a problem.


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## Muratozt (Mar 27, 2021)

Hi, I thought the same way, opened the solenoid valve, descaled it and cleaned the hard black crap inside it. However this did not stop the drops completely. I think we can make sure only when we know the answer to this question: does solenoid valve close the connection between boiler and brewhead while steaming? If yes, these drops should show a malfunction. If no, we should look for the answer elsewhere


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## MrShades (Jul 29, 2009)

Muratozt said:


> Hi, I thought the same way, opened the solenoid valve, descaled it and cleaned the hard black crap inside it. However this did not stop the drops completely. I think we can make sure only when we know the answer to this question: does solenoid valve close the connection between boiler and brewhead while steaming? If yes, these drops should show a malfunction. If no, we should look for the answer elsewhere


 Yes, it SHOULD close the connection between boiler and group when steaming - but only if it's able to seal properly and there isn't scale or something causing the seal to not be made. So if you have drops when steaming, it's probably a good idea to clean the solenoid valve properly.


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## Muratozt (Mar 27, 2021)

Thanks for the answer MrShades. Do you have an idea what could be the reason other than scale? I removed the solenoid valve, cleaned the stuck black particles that I saw in it, submerged under Gaggia descaler for half an hour. I even did a full descale to the machine after that. But drops are still there. My machine is 1,5 months old.

I do the trick of starting steaming before steam light turns on (so assume that I steam around 150 degrees). Do you think this could have damaged the valve by burning an invisible gasket inside or etc?


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## yardbent (Aug 8, 2015)

MrShades......advice needed please.........

*#1*...........I leave my 2010 GC 'ON' for 15mins to warm the machine up; with a large cappuccino cup on the drip tray

then Brew switch ON to warm the cup = a MASSIVE CLOUD OF STEAM and hot water









during your PID install ; (with boiler out ) anything I should inspect/clean....?

COFFEE COMPASS says to set the PID to brew temp to 93degC with the beans I have

*#2*..........I've read a few horror stories about the switch panel housing snapping

can I get the boiler out with the switch panel in place..?

regards.................john


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## HDAV (Dec 28, 2012)

I would replace everything all the o rings while it's apart and clean the boiler

shouldn't get steam from group unless steam is selected on panel possible stat issues?


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## robmack (Apr 2, 2021)

Do you have an offset programmed into the PID? This is the actual difference in temperature between the water temperature at the group versus the temperature measured by the RTC on the boiler. Since it's not possible to measure the actual temperature at the group head, the offset programs the PID to show what it thinks would be the temperature but the PID will actually heat the water in the boiler to a higher temperature to account for the loss in temperature as the water flows from the boiler to the group. So if the programmed offset is too much, the water will be over heated and you'll get steam from the group head (i.e. the water from the group head is hotter than is indicated on the PID display). There is a method for determining the correct offset value to a degree of accuracy ( https://www.home-barista.com/espresso-machines/getting-accurate-shot-temperature-displays-on-pided-double-boilers-without-thermometer-t54897.html ). It's only until you can accurately match the group head temperature to the PID displayed temperature that you can expect to set the proper values for the coffee you are using.


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## larkim (Sep 3, 2018)

At the risk of reviving a very old post, the diagram in here is really helpful to describe how the internals work. But it would be also really helpful if it could be extended to include what the electrical "flow" is also like just for clarity, including what happens with the 3 way valve as activated by the solenoid.

My understanding is as follows:-

(0 - 0 - 0) All off - nothing powered. 3 way valve - open from boiler to dump tube, closed from boiler to group head.
(1 - 0 - 0) Power switch - on. Steam and brew switch - off. Boiler heating to brew temp (subject to brew thermostat). 3 way valve - open from boiler to dump tube, closed from boiler to group head. Pump inactive.
(1 - 0 - 1) Power switch - on. Steam - off. Brew switch - on. Boiler heating to brew temp (subject to brew thermostat). 3 way valve - closed from boiler to dump tube, open from boiler to group head. Pump active. 
(1 - 1 - 0) Power switch - on - Steam - on. Brew switch - off. Boiler heating to steam temp (subject to steam thermostat). 3 way valve - open from boiler to dump tube, closed from boiler to group head. Pump inactive.
(1 - 1 - 1) Power switch - on. Steam - on. Brew switch - on. Boiler heating to steam temp (subject to steam thermostat). 3 way valve - closed from boiler to dump tube, open from boiler to group head. Pump active.
Is that correct? I've made an assumption that the 3 way valve is normally open to the dump tube. Just out of interest, if that is the case why does steam not escape through the dump tube when on position 1 - 1 - 0?


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