@kimot Ironic then is it not that the same "random event" I was chasing occurred whether using the Whisper, a 3v8MHz or a 5v16MHz Pro-mini?
I thought that rather narrowed causes to program or sensor, but hey, I'm no expert.

As you might note above I had also excluded EMI effects through experiment

@kimot You may be assured I never cease to be surprised, particularly by presumptions...
It is a "Whisper Node AVR", full blown 16MHz 3.3v Arduino with onboard booster and rfm69 etc, too clever for me to consider attempting to build at the time... Your apology is accepted.

@avdhil No I didn't, only because I got diverted on more critical nodes and it has been on my to-do list ever since, aka forgotten...
It has been on batteries only and re-located, so external stray effects are nulled, but it still throws the oddball.
Spoke with Elster techs who advised it is impossible for the PR6 to signal in error, but being an Arduino tinkerer himself, suggested refining the program to verify the interrupt was a valid INT1 before incrementing the value.
I simply never got round to trying it, and as not able currently, perhaps worth a try....

@fredswed And by extension (Possibly Swedish water suppliers differ from UK or Romanian counterparts?) the data retrieved from their devices is often regarded as their property also, and brick walls begin to appear ino what should be readily shared data. If they will not share, fitting a downstream device within your own control can often be the only solution, don't interfere, augment...

As a perverse example, my own gas and electricity suppliers are the German monolith EON who provide and enable access to their 'graphs' online, updated with 1 or 2 month readings (gas and electricity).
Having checked the base data for their graphs, I realised they were presenting a lovely graph based on complete bunkum, and developed and maintained my own ever since, which IS accurate. I checked recently and their graphs are still pretty but complete rubbish.
Installing a gas meter sensor caused EON palpitations until they realised it was the commercial device for the meter and could not object on technicalities then quietly dropped objections, I don't care how they respond when I fit meters to the Consumer box, it is nowhere near their SMART meter which tells me nothing but tells them much, mainly that I halved their 2 monthly bill .
If the service provider will allow detailed sharing of YOUR data, all good and well as it is mutually beneficial, but if not, easy enough to solve at your own expense.
I fitted two replacement upgraded radiators in the last month, somewhere a Romanian regulation lurks that I should not have done so, but the insurer doesn't give a damn unless it is found to have caused the demise of the insured property.. Is it worth the risk? Hell yes...

@bjacobse Pardon my laughter, insurers look for any excuse for sure, but I have never heard yet where a water meter or any other competent insertion damaged a building, let alone an insurance company refused to compensate for a building which burned to the ground (99.9%) on the basis the water meter was not a verified install. For sure some loss adjusters will use any excuse, but really?
To clarify, in many countries a certified inspector or Engineer must certify that work is carried out within the regulations, it does not state that HE/SHE has carried out the work, only that it has been inspected and verified as compliant. You know any certified local plumbers with 5 minutes to spare, because that is how long it takes me to fit one, and about the time it takes a certified pipe-jockey to verify it's right and sign it off, if it really concerns you ?

I have 2 self fitted water meters with sensors, gas meter sensor etc, and a huge amount of DIY stuff any smartass insurer could IMPLY was a contributory factor to the disaster which befell my house, but frankly it wouldn't stand 1 second in Court before being laughed out...
Place hasn't burned down yet, fallen over in earthquakes, or been subjected to landslide, but luckily I don't have Swedish Insurers....
PS- I should clarify that the standing regulations are framed to quite rightly protect consumers as well as the service provider against cowboys interfering with apparatus. Changing light switches or sockets falls under the same overall umbrella despite everyone and their mother changing them.

@dzjr said in 2 dallas temp + 4 relays:

By the way, if I disconnect one sensor, another sensor is set it place at the controller, if it is connected again then it is back to the original ID.

This is where the array method is advantageous, the child-IDs of the chip addresses are fixed consecutively in the array, remove the chip from the line and it's place remains vacant until replaced.

@bjacobse Another option perhaps to consider (if it is physically viable), is to insert a meter and sensor of your choice within your property, they are not expensive nowadays and easy enough to fit ?
A simple meter and reed switch such as this link text or similar perhaps.

@bjornhallberg Suggest you discuss with your water supplier, and see what THEY intend to deploy for comms and explain what your own objectives are, that may refine what you are looking at, and they MIGHT actually help rather than be play "stupid" which is unfortunately common nowadays. In all probability they will be looking at wireless m-bus for drive-by readings, this is the predominant method of retrieval.
I admit to surprise at them deploying ultrasonics, they are on the expensive end of the market but they are extremely reliable and accurate.

@sunnyboy69 Getting false readings can be anything as it depends if it is a serial read from the device or simple timing of the echo, unstable voltage, or even an object caught in the path of quite a wide cone, but without further details it is impossible to identify. I've been caught before with a serial reading device, took a while before I realised....
An extension of what @bjacobse suggested is to repeat readings until you get two identical consecutive results which are <> known limits and not cuckoo results..

@w1ldf1re While you are waiting...
Pardon my interest and confusion, but if your Danfoss stat (presumably from a single area sensor) is controlling the boiler, how does the Cube connect to it, and if the Danfoss is connected, why does the boiler run all day?
The discontinuation of the Cube compatible boiler relay due to lack of sales put me off the Cube, and quite a few complaints over reliability sealed it.
My next notion was to go for a Pi3 Homematic controller which was allegedly Max compatible (see https://www.elv.de/funk-system-homematic.html - Bausatz) but when prices shot up I abandoned it for better valves/TRVs instead.
Right now I'm looking at paralleling the existing commercial (Danfoss type) boiler relay with an Arduino fired one fed temperatures for all the rooms to cope with deep winters where the top floor can plunge, but they are quite separate controls.
If you can find a relay (Schaltaktor) which can be called by the Cube, you should be good to go, the parallel system I would suggest better in case your Cube has a brainfart... Just my 2c...