# Boiler thermometer



## Wando64 (Feb 28, 2011)

I have installed a thermometer with a thermocouple attached to the boiler of my Silvia (£7) and made some interesting observations.

With a PID installed, I assume the temperature shown would be very stable, i.e. the temperature on the outside of the boiler is presumably the same as that of the water inside.

Conversely, when reading the temperature with a thermometer the value is constantly changing i.e. either the water is cooler than the boiler and the boiler is cooling down, or the water is hotter and the boiler is warming up.

An obvious example of this is when the boiler element switches off, yet the boiler temperature carries on increasing by as much as 2 degrees C over the following 20 to 30 seconds indicating that the water inside was much hotter.

To cut a long story short, the temperature measured on the boiler seems to tell little about the water temperature inside, unless kept constant for a period of time by a PID.

Do my (not very scientific) observations and conclusions match your experience?

If so. has anybody found a way to minimise the problem so that a thermometer becomes useful beyond the point of helping making more or less interesting observations?


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## RoloD (Oct 13, 2010)

To be blunt, I think people put to much faith in PID controls, particularly on small machines. What we really want to know is the temperature of the water as it passes through the coffee, and the temperature of the group itself could (I would think) have a significant effect on the temperature of the water after it comes out of the boiler.

Also, I am not sure how you are measuring the temperature of the water inside the boiler - isn't the PID thermocouple screwed into the wall of the boiler rather than into the water inside the boiler? (I always assumed it was in the case of the Gaggia Classic to which I fitted a PID control - please correct me if I am wrong). Perhaps what you are measuring is the temperature at different parts of the boiler. And, as you suggest, the temperature of the water may differ from the temperature of the boiler housing.

Although I believe a PID control does help with temperature stability on a Classic or a Silvia, it doesn't completely overcome the inherent temperature problems of a single boiler/dual use thermoblock machine.

The important thing, however is - what does the coffee taste like?


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## Wando64 (Feb 28, 2011)

I don't have a PID, I just have a thermometer with thermocouple attached to the top of the boiler.

Coffee tastes great if I follow my tried and tested surfing routine. It leads to a temperature of 108C (on the boiler) at the point of pulling the shot.

However, if I reach the same temperature without following my routine (e.g. by switching the boiler on manually with the steam button) the results are not the same, hence the conclusion that a given temperature on the surface of the boiler does not imply a constant and repeatable temperature of the water inside it.


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