# How Thermally Consistant Are HXA machines k7?



## vancutan (Feb 11, 2017)

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just a passing thought really. as i understand it, the boiler is running at steam temp, and brew water passes through it, heated as it does.

If the machine has been sitting for a while you give a cooling flush

but surely any water in the system will be warming up to approaching steam temp as soon as you've flushed, so surely if you flush and then spend 10 seconds getting ready you get a different temp to if you flush and spend 30 seconds etc

so rather than the single boiler where you know the water has reached the set temp because it's been there 20 mins at least, with a hx you hope it passes through at the right time to get tot he right temp

it seems to me that it's very variable - is it?

or have I got it completely wrong?

The more I learn, the less I know!


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## MediumRoastSteam (Jul 7, 2015)

This video illustrates a few things:






However, I don't understand the details of the why's and what's, so I am sure someone here can explain things.


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## emin-j (Dec 10, 2011)

When I bought my HX machine I took some temperature readings with a thermocouple probe, after a cooling flush (the boiling water stops dancing plus a bit more ) it then takes around 40 seconds for the water to reach brew temperature so I used to start my timer (30 seconds) in that time I connect the portafilter and place my cup(s) on scales, then at the 30 second point I pull up the brew lever it then takes approx 5-6 seconds for the coffee to start flowing from the portafilter, in that time the water temperature should be close to perfect. After owning a HX machine for a while it becomes a simple routine.


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## mremanxx (Dec 30, 2014)

Interesting, would have thought that the brew temp was a bit low, no?

Always feel brew temp is a hit or miss on my HX machine, especially when using light roasts as I find they are more temp sensitive.

Considered getting a thermometer for the brew head but looks ugly.

Does anyone know of PID kits for HX E61 machines or are the electrics too complicated normally to retro fit easily?


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## MediumRoastSteam (Jul 7, 2015)

mremanxx said:


> Interesting, would have thought that the brew temp was a bit low, no?
> 
> Always feel brew temp is a hit or miss on my HX machine, especially when using light roasts as I find they are more temp sensitive.
> 
> ...


PID on an HX machine has not the same effect as a PID on a dual boiler machine.

When an HX machine has a PID, it performs the same function as the Pressure Stat: It controls the temperature inside the boiler. The higher the temperature, the higher the pressure. The difference being that a PID will control the temperature, and the Pressure stat will control the pressure, but both will translate to the same thing.

The temperature inside the boiler of a HX machine is set to be around 126 degrees or thereabouts, equating to 1.3bar pressure or thereabouts. Some machines are set to be less, like the Rockets usually set to around 1.0 bar pressure.

You have boiling water to produce steam inside the boiler. When you brew coffee, water is drawn from the tank (or mains) through a pipe that goes through the boiler - thus a Heat Exchanger design. That water gets heated in the process and the design aims to deliver water at brewing temp for expresso at the group.

When you leave the machine idle, that water gets super heated, hence the cooling flush usually needed.

Just google "Heat Exchanger espresso machine". There are tons of explanations and diagrams.


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## mremanxx (Dec 30, 2014)

Cheers for the information roughly knew how it worked, just not as well as you explained it. So without a thermometer in the brew head brew temp is hit or miss affair then? If that is the case you would think more options like an Erics thermometer would be available no?


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## MediumRoastSteam (Jul 7, 2015)

mremanxx said:


> Cheers for the information roughly knew how it worked, just not as well as you explained it. So without a thermometer in the brew head brew temp is hit or miss affair then? If that is the case you would think more options like an Erics thermometer would be available no?


I suppose. You basically need to understand how your machine works, in terms of length of the cooling flush and recovery time. Once you work that out, then they are quite consistent.

I owned an HX very briefly and it's a bit of a learning curve. Eric's thermometer would certainly help, at least until you understand the behaviour of your machine. I suspect after that you just get used to the ritual and becomes routine like one of the earlier post suggest.

PS: Even on a dual boiler what you read in the PID is not the accurate temperature in the group. The value displayed in the PID display for the temperature in the brew boiler is the temperature measure in the brew boiler, and not at the group. Some machines allow you to set an offset. For example, mine is set to 15, meaning that, then the temperature in the boiler is 105C, the PID display would display 90C.


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