BarcaBere wrote:... older (he says 90's) model Cimbali Junior D/1 for a long time and never has had any problems.
Three things ...
The first one would be to check the D/1's age.
Look under the drip tray and you should see a sticker like this one:
A bad photo but in the lower right hand area you can see the manufacture date.
If the stcker is not there it may be elsewhere on the unit, that info will give you the max age of the machine.
The second would be to ask your friend if he purchased the Cimbali 'new' or not and when and the third (and most important) would be to ask him if the unit has had any
maintenance in the span of time he has been using it. If it has, what type.
When I purchased my D/1 (ca. 2000) it had been used for a very short time before the owner grew weary of it and replaced it with one of those Nespresso (!) things, leaving it in a corner to gather dust for a about four or five years till his wife grew weary of it, so it was put up for sale along with an equally unused Junior Max.
US$450 and a cab ride later, a thorough check up of the D/1 revealed that even with very little use, it needed some cleaning up and descaling: the water at this chap's home was sourced from a deep well in the suburbs and quite hard.
It could well be that this D/1 has had litle or no service at all in many years and at this point it would be worthwhile checking out the machine for scale build-up, which depending on the water supply, could be significant for any ca. 90's machine without proper maintenance.
Scale build-up will be found in the boiler, the HX, the boiler level rod, the pipes connecting the boiler to the to the PS and manometer and sometimes even at the manometer's base, all of which which would certainly cause the symptoms it is now showing.
You will also find scale build up in the piping to the 3-way valve and in the valve itself.
Now, all this happens inexorably
over time, slower or faster depending on a) the type of water used and b) the maintenance schedule of the unit has had, it is only a question of when
BarcaBere wrote:... device overheats and over-pressurises.
... water is also way too hot, even at 'lower' pressures ...
Water and pressure are directly related so if the boiler output is 'too hot' at a 'lower' pressure, there is a problem with one of the instruments indicating either that the output is 'too hot' or that the pressure is 'normal' or a combination of both.
BarcaBere wrote:... not seen the safety valve open yet ...
If the safety valve has not blown I'm inclined to think that the valve's operating pressure has not been reached as the safety would have tripped.
BarcaBere wrote:... the heating element just keeps on heating the boiler.
Like kolu has mentioned, pressurestat membranes harden over time.
Actually, what happens is that (in most pressurestats) they progressively lose flexibility
and lose their plane, deforming ie: develop a bulge.
When this happens, the deadband increases to the point of making it unrealiable for proper use. With an extra large dead-band, the PS can eventually start to cut off at a point where a safety pressure/temperature limit has been passed, which is what seems to be happening here.
For a Sirai pressurestat you can get a membrane repair kit like the one I posted here:Sirai pressurestat membrane replacement
It is not a difficult procedure but you have to be careful with the four small metric screws holding the membrane: they can strip easily.
(no, don't ask).
BarcaBere wrote:Replacing the safety thermostat seems to be easy ...
If it is the stock safety TS that came with the D/1 it is probably an auto-reset type one and being so, it has probably tripped and gone unnoticed as it resets itself when the temperature goes back to it's nominal setting. That would be the reason the safety valve has not blown.
recommend that you change the original auto-reset part for a manual reset type one like the one I mention in this post:La Cimbali Junior - Replacement Heating Element Different
As you are aware, mounting it with thermal grease is of good practise.
BarcaBere wrote:... should replace the whole thing ...
The usual Sirai pressurestats you find in older commercial espresso machines like this one are built like Panzer tanks and made to last for a great many cycles under severe conditions, much harsher than the use they have been put to in a Cimbali D/1.
The original unit probably is a model with two sets of contacts.
Check them out and if one is worn or pitted by arching you can switch to the unused one and get many years more service from it.
BarcaBere wrote:... help or tips much appreciated ...
A search here at HB will yield a huge amount of pages related to maintenance of any HX machine, Cimbali D/1, other Cimbali models and even similar rebranded units with common maintenance procedures.
Do keep us posted on your progress.