# Heat exchanger descaling and sour milk



## mompt (Oct 25, 2012)

Hi guys,

Just a few questions to throw out to those of you who have a heat exchanger machine or have restored a badly misused HX machine.

I recently bought myself a 2nd hand Izzo Alex MK2 - the HX model rather than the duel-boiler. It's about 5 years old and had been used in an office environment where it was completely neglected and misused. At first glance I had little faith it would work at all, but turns out that all components are fully functional etc. I had to replace the gasket and shower screen to start with (old gasket was so dry and cracked that it would simply fall out of the machine). The boiler was absolutely full of filthy water - and I mean filthy couldn't even see through it in a glass it was that brown so I ran 3-4 tanks of water through it until it cleared up.

After that, I ran two domestic descales through it according to this walkthrough and a few other youtube videos:

http://www.1st-line.com/techsupport/periodic_maintenance/descaling_heat_exchanger_traditional_espressomachines.htm

I ran maybe 6-8 tanks through of fresh water through the machine and the water seemed to have cleared up completely - apart from a few particles or scale that were still in the boiler (I given the condition of the boiler that's going to be an ongoing thing until all the scale eventually clears)

I then went on a 6 day holiday, and upon returning I decided to make myself a latte. My god I have never tasted anything so putrid and sour. I had a play around and turned on the hot water tap to check the condition of the boiler and to my surprise the water was very blue. So turns out I still had quite a lot of descaler left in the boiler.

So today I decided to have a further go at cleaning up the machine. I checked the water coming out of the group head. Gave it a smell and a taste, and apart from being hot, it didnt smell or taste much different to hot water out of the kettle. Then I decided to steam some milk and to no surprise, the milk tasted horrid. So then I ran maybe 10 or so full tanks worth of water through the boiler to eventually significantly reduce the discolouration and the odd tangy taste, but I would still say that steaming milk results in an odd taste - nowhere near as bad as initially, but still a little off.

Can anyone else confirm whether they have had such issues after descaling a large boiler heat exchanger or have I got more of an issue on my hands.


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## jimbow (Oct 13, 2011)

The problem is that unless you disengage or disable the autofill feature then you will not be able to effectively flush the descaling solution from the boiler - you will simply be [very] gradually diluting it.

The easiest way to get around this is to switch the machine on and let it get up to operating temperature. As soon as the boiler pressure reaches the top of its pressurestat swing and the heating element switches off, switch off the machine. This will prevent the boiler from autofilling when we start draining it in a moment. Now open the hot water tap and allow the residual pressure in the boiler to force out the water. Allow as much water to drain out as possible before turning off the tap.

Make sure the water reservoir is full of fresh water and then switch the machine back on. The pump will immediately begin refilling the boiler with fresh water from the reservoir. Once the machine is back up to temperature, the process can be repeated as necessary.


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## mompt (Oct 25, 2012)

yeh tried this... Did about 3 tanks worth. Still an odd smell with the steam. And quite the odd taste with the milk. Might need to do a deep descale of the whole machine. Pull apart and soak components overnight in an citric acid bath or on the stove top.

Anyone have suggestions and tips on doing a deep descale?


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## RisingPower (Dec 27, 2009)

There's the guide that bella barista produce, basically fill up with descaler, run descaler through the grouphead with some backflushes, turn off, leave 30 minutes, turn back on, more flushes through grouphead, run small amount through steam wand, hot tap.

Turn off, fill with clean water and run through hot tap, backflushes and wand, quite a few times, more than 3.

The only issue is, water doesn't really fill the boiler enough, so you end up turning it back on again a few days later to find the water is blue and sour again. I think it would probably be best to let it totally cool down before flushing it entirely, but then again, I have rocked it to rinse the boiler sides (I know you're not supposed to).

You can empty the boiler with the hot tap to your hearts content for numerous sessions of flushing and imho if you don't rock it slightly it doesn't rinse out the boiler top/sides, so that just cools and ends at the bottom of the boiler next time.

I'd just flush it a fair few times again, if it's sort of a sour milky smell. Also do you see very sort of fine grayish liquid if you steam into a mug?


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## mompt (Oct 25, 2012)

Cheers for the tip there risingpower. I'll give that a go as well. I'm not even sure that it's the descaling acid solution that's the issue any more. I've done so many complete drains of the boiler (over 20 tanks now) that surely it cannot be that any more. I'm more concerned about the scale, dirt, muck and all sort of other substances that may still be in the boiler that is resulting in this alteration of the taste of the milk. The group head water is absolutely fine but the boiler water and steam still smells odd. The next best thing is as I said before, perhaps a complete disassemble and deep cleaning the machine. Acid bath for the boiler and pipes I guess.

I'll see how I go with the tilting and swirling the machine. It's one heavy beast though 30kg or so.


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## RisingPower (Dec 27, 2009)

mompt said:


> Cheers for the tip there risingpower. I'll give that a go as well. I'm not even sure that it's the descaling acid solution that's the issue any more. I've done so many complete drains of the boiler (over 20 tanks now) that surely it cannot be that any more. I'm more concerned about the scale, dirt, muck and all sort of other substances that may still be in the boiler that is resulting in this alteration of the taste of the milk. The group head water is absolutely fine but the boiler water and steam still smells odd. The next best thing is as I said before, perhaps a complete disassemble and deep cleaning the machine. Acid bath for the boiler and pipes I guess.
> 
> I'll see how I go with the tilting and swirling the machine. It's one heavy beast though 30kg or so.


If you have put that much water through it, yeah, worrying.

Short of taking it apart, not sure what you can do, no idea how much a replacement boiler costs or how you'd even pull apart the heat exchanger. I've only changed the pstat and the little valve that sits down at the bottom front of the izzo, with the braided hose.

I take it you've pulled the e61 head apart and looked at inside? Specifically the top filter.

I found after descaling, both the steam smelt sour and the water from the group head, until I rocked the izzo gently then put a few tanks through from cold. Be gentle









I'd really like to know what is in the boiler if it's worse than scale.

Coffeetime may have some diagrams of the internals of the alex, failing that you could try and get in touch with bellabarista.


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## mompt (Oct 25, 2012)

RisingPower said:


> I found after descaling, both the steam smelt sour and the water from the group head, until I rocked the izzo gently then put a few tanks through from cold. Be gentle


worked wonders... Steam is still a little odd in smell but much better. And the steamed milk has almost no distasteful traces. Either that or I've completely desensitised my taste buds with bad milk :/

Well, I guess that's the last time I'm going to do a back to back double descale.


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## rmat (Aug 25, 2012)

I found these links helpful:


http://coffeetime.wikidot.com/descaling-brass-and-copper


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## jimbow (Oct 13, 2011)

Out of interest, what are you using as a descaling solution? Citric acid tends to foam and 'cling' to surfaces - this is one of the properties that makes it so good as a surface cleaner for bathrooms, etc. Some of the compound descaling solutions e.g. Dezcal include additives that reduce the foaming and make it easier to flush.


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## mompt (Oct 25, 2012)

jimbow said:


> Out of interest, what are you using as a descaling solution? Citric acid tends to foam and 'cling' to surfaces - this is one of the properties that makes it so good as a surface cleaner for bathrooms, etc. Some of the compound descaling solutions e.g. Dezcal include additives that reduce the foaming and make it easier to flush.


I used 2 sachets of Puly Cleaner Descaler. I thought it was citric acid based descaler, correct me if I'm wrong though.


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## espressotechno (Apr 11, 2011)

Nope - Puly Descaler is sulphamic acid (No - NOT sulphuric !). It's a coffee industry standard descaler.


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## RisingPower (Dec 27, 2009)

mompt said:


> I used 2 sachets of Puly Cleaner Descaler. I thought it was citric acid based descaler, correct me if I'm wrong though.


Urr.. I'm not entirely sure, but then again I use pure citric acid in mine for descaling.

Buy a bag of anhydrous citric acid, use that next time.


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