Boiler water temp higher than maximum?

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Bartb
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Boiler water temp higher than maximum?

Post by Bartb »

Hi all,

Installed my OTGW and have it integrated in Domoticz.
All seems working fine as far as I can see.

Two questions though:
1] I'm trying to set a maximum boiler water temp. I'm using the command SH for this in OTMonitor (Max CH water setpoint)
Although I set SH to 35 and I get this confirmed in the interface log, it still shows the Boiler water temp reaching over 40 degrees from time to time.
It looks like the max setting is ignored?

2] When I set SH=50, it confirms the value by stating SH=50 in the log.
My log now says:
15:24:48.723198 BC0313200 Read-Ack Max CH setpoint boundaries: 50 0
15:24:49.034869 B40392300 Read-Ack Max CH water setpoint: 35.00

When I try to set the max temp to > 50 , I get a SH=BV (bad Value) message returned which is in line with the log msg.
I see this boundary is set by the boiler, but I would expect my boiler (Remeha zTerra Ace) to be able to reach 80+ degrees if requested?
Can I somehow overwrite the given boundaries 50 to 0?

Hope anyone can help out.

Thanks.
________________
Boiler: Remeha Tzerra Ace 39C
OTGW (Nodo-shop)
Thermostat: Nefit Easy + Easy connect adapter for OT
hvxl
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Re: Boiler water temp higher than maximum?

Post by hvxl »

Your boiler indicates that the max CH water setpoint can be configured via Opentherm. But I have seen logs from other people as well where the water temperature exceeds the control setpoint, which the thermostat has set to the max CH water setpoint. This can happen when hot water has been used and the DHW setpoint is higher than the max CH water setpoint. But I've also seen it happen when there has not been any DHW demand. In my opinion such boilers are not behaving correctly.

The BV response is given by the OTGW when the value of the SH command is outside the limits given by the boiler in the Max CH setpoint boundaries message. I agree that 50 is a very low upper boundary for the CH water temperature. Maybe this has been configured by the installer because (he thought) you have floor heating? Looking through the parameters of the Tzerra, my best guess is that this may be set in CP000.

Some other boilers have a bug that they report the current max CH setpoint as the upper boundary. So, once the max CH setpoint has been lowered, it can not be raised again. A work around for this bug is to tell the OTGW that the boiler doesn't support the max CH setpoint boundaries message (UI=49). Then reset the OTGW to make it forget the boundaries it has collected before (GW=R). Now the OTGW will use its default boundaries of 10 and 90. You can try to use the same procedure to see if the boiler will accept a max CH setpoint higher than 50. But I expect that it will return 50 in the Write-Ack on a Write-Data of MsgID 57 with a value of 60, for example.
Schelte
Bartb
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Re: Boiler water temp higher than maximum?

Post by Bartb »

thanks for the info.

I do remember the installer asked me about the max temp. I have floor heating downstairs, radiator heating upstairs.
I checked and indeed it was setting CP000 on the Remeha Tzerra Ace that was set to 50 degrees.
Just to have the flexibility I now increased it back to 80, but ... SH=60 still gives me a BV.
To try I also increased CP010 (max temp if no room/outside temp), as it was also set to 50, but no luck.
I'll search a bit more for such setting...

Wrt. the Max CH water temp: I indeed saw the CH water temp rise to much higher values every time DHW is used, but I also see an overshoot (like 45 degrees where I had set the max to be 35), which should not happen. It doesn't really bother me, but its useful to know.

Thanks for your answer!
Last edited by Bartb on Sun Dec 11, 2022 4:23 pm, edited 2 times in total.
________________
Boiler: Remeha Tzerra Ace 39C
OTGW (Nodo-shop)
Thermostat: Nefit Easy + Easy connect adapter for OT
hvxl
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Re: Boiler water temp higher than maximum?

Post by hvxl »

The OTGW will only learn about the new limits when something requests MsgID 49. The OTGW itself only does that once after a reset. If the thermostat also doesn't request this information, then you may have to manually force it using a PM=49 command.
Schelte
Bartb
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Re: Boiler water temp higher than maximum?

Post by Bartb »

hi.

Thanks. I tried what you said.

On the boiler I made sure I set CP000 to 80.
(I also set CP010 back to 50 as I realised this is a 'fail-safe' value, and I want to keep it)

Then I pressed the reset button on the OTGW board (resent version bought from Nodo-shop) for about 3 seconds. All leds switched off en came back, as it seemed to nicely restart.

After sending SH=60, it still returned the BV value.

Then I sent PM=49 and got PM: 49 as response back.
After that I again repeated the SH=60 value but still the BV response :(

Am I doing something wrong here?
________________
Boiler: Remeha Tzerra Ace 39C
OTGW (Nodo-shop)
Thermostat: Nefit Easy + Easy connect adapter for OT
hvxl
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Joined: Sat Jun 05, 2010 11:59 am
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Re: Boiler water temp higher than maximum?

Post by hvxl »

You have to understand that the PM command will queue the message to be sent at the first opportunity. So, you have to wait for that to happen before the effect would be visible. However, if you still get a BV in response to SH=60 after a reset, the OTGW must have received stricter boundaries. It starts with 10..90 degrees. Apparently the boiler still sends 50 as the maximum. You can confirm this by looking at the logs.
Schelte
Bartb
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Re: Boiler water temp higher than maximum?

Post by Bartb »

I managed to increase SH to above 50.
It turned out its not (just) setting the code CP000 to 80 on the Remeha Tzerra Ace, but rather (or also?) the max temp value before you even go into the menu of the boiler.
See below: In case anyone has the same issue in the future, I’ve added the part where it’s described in the manual:
7B01452C-D67A-4994-8E3B-CE5C521B4472.jpeg
7B01452C-D67A-4994-8E3B-CE5C521B4472.jpeg (50.67 KiB) Viewed 2724 times
01B717D5-F2ED-4F8A-BAD1-CE60F8AA0E0C.jpeg
01B717D5-F2ED-4F8A-BAD1-CE60F8AA0E0C.jpeg (90.28 KiB) Viewed 2724 times
The manual states that when using Opentherm (and in my case weersafhankelijk), it should be adjusted automatically, which In my case it didn’t.

Anyway, problem solved :P
________________
Boiler: Remeha Tzerra Ace 39C
OTGW (Nodo-shop)
Thermostat: Nefit Easy + Easy connect adapter for OT
hvxl
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Posts: 1965
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Re: Boiler water temp higher than maximum?

Post by hvxl »

An opentherm controller can adjust the max temperature setting, but only within the advertised bounds. So the boiler should provide the correct bounds in MsgID 49. Have you checked that they were still wrong before you made the change on the boiler? And did changing the temperature on the boiler make any difference in the values reported in MsgID 49?
Schelte
Bartb
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Re: Boiler water temp higher than maximum?

Post by Bartb »

Interesting indeed.

Yes, the boundaries were still 50 to 0 before I changed the setting on the boiler.
After I set the boiler to 80, I didnt check the string of values itself (PS=1), but I did send a PS=0 command straight after which then resulted in updated boundary values "80 0" in the "statistics" tab in OTMonitor app. I guess this tells that it worked. To confirm the correct working, I then set SH=75 which was then confirmed with a SH=75 response (msgid 57).
See pic below.
ot.jpg
ot.jpg (63.01 KiB) Viewed 2566 times
Thanks again.
________________
Boiler: Remeha Tzerra Ace 39C
OTGW (Nodo-shop)
Thermostat: Nefit Easy + Easy connect adapter for OT
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