Opentherm counters are limited to 16 bits

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Opentherm counters are limited to 16 bits

Postby Digit » Sat Nov 10, 2012 10:54 pm

I saw some strange numbers arriving in my system earlier this evening and just wanted to share that, so you won't start looking for a non-present bug like I did, for 10 minutes or so :lol:

While looking at the incoming information from my Opentherm Gateway, I saw something strange today.
Here's a small piece of the information:
Capture_02 2012.11.10 22.36.20.jpg
Capture_02 2012.11.10 22.36.20.jpg (24.63 KiB) Viewed 1875 times

The number 65535 immediately caught my attention, for the obvious reason - can't be a coincidence, right.. :)
So I had a look at the information from my Remeha Recom Interface, this one told a completely different story:

Capture_03 2012.11.10 22.39.15.jpg
Capture_03 2012.11.10 22.39.15.jpg (10.83 KiB) Viewed 1875 times

My first thought was that there must be something wrong in my Opentherm Gateway frame decoding, but that was not the case.
The fact is, that Opentherm can only handle 16-bit unsigned values for the Data ID regarding the number of burner starts! (Data ID 116 (decimal), Type u16).

So if you're connecting the Opentherm Gateway to a central heating that has been operational for some years (mine: 3), you can expect some "strange" numbers!
So remember this; 16 bit is the max!
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Re: Opentherm counters are limited to 16 bits

Postby hvxl » Sun Nov 11, 2012 4:07 pm

Digit wrote:So if you're connecting the Opentherm Gateway to a central heating that has been operational for some years (mine: 3), you can expect some "strange" numbers! So remember this; 16 bit is the max!

You can reset the counters using the RS command of the opentherm gateway. I did that after the biennial service of my boiler. Admittedly, that was mainly to test if the commands worked, but as a result my counters are nowhere near the maximum after 3.5 years :D
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Re: Opentherm counters are limited to 16 bits

Postby Sall » Thu Mar 21, 2013 8:06 pm

I have a question about the counters (Opentherm IDs 116 to 119). Is it possible, that the gateway simulate the counters if the CV don't support them?

I have just build my first OTG but can't test it, because I have no Opentherm regulator for now. Next week I will get an iSense for my 8 years old Remeha Quinta 10. So in the meantime I read all the documentation. It seems so that the old Quinta don't support the counters, since a Remeha Quinta 35c (http://www.tclcode.com/opentherm/matrix.cgi#boilers) have the same MCBA board, which have no support for the counters.
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