AWB boiler 3HR 28T control panel blocked

[uef]

I've a problem with my AWB 3HR 28T boiler when connected to OT master:

when master sends status exchange messages (ID=0) the boiler changes it operation mode to "CH enabled & DHW enabled" and it's no longer possible to change the operation mode manually on the boiler control panel (other parameters like e.g. CH temperature can still be modified).
(with operation mode I mean any combination of CH on/of and DHW on/off).

The given behavior seems to be INDEPENDENT from content of Master status byte (high byte) in message ID 0: even when this is set to 0x0 (CH off & DHW off) it behaves the same.
Once the boiler is disconnected from master it returns to it's former operation mode (e.g. only DHW enabled) and allows manual change of operation with control panel.

The OT communication is working well in general: boiler reports all relevant values and also sends a valid slave status reply on message ID 0 e.g. for flame status .

The issue is that I don't want to have CH enabled in the summer just to be able to log slave status.

Is this general behavior of OT boilers or specific for this boiler or must be a bug ?
Any ideas how to proceed ?

Thanks
uef

[hvxl]

The installation manual of the AWB 3HR 28T indicates for operation mode and a few other settings:

• Bij een OpenTherm (modulerende) kamerthermostaat, vervallen de instelfuncties op de ketel. Deze zijn instelbaar op de kamerthermostaat (afhankelijk van het model kamerthermostaat).

Translation:

• With an OpenTherm (modulating) room thermostat, the control functions on the boiler no longer function. These can be set on the room thermostat (depending on the room thermostat model).

How do you determine that the boiler changes its operation mode to "CH enabled & DHW enabled"? Are you looking at the display of the boiler? Then that may be just the way the boiler indicates that the thermostat can control both parameters. Or does the boiler actually set the CH mode and DHW mode bits in the slave status byte of MsgId 0? That would be unusual.

[uef]

You sent me right direction (and thanks mentioning the installation manual - I didn't know so far).

Yes, I relied on the display of the boiler which shows "CH enabled plus DHW enabled" as soon as I send ID=0 messages - independent of the content of the master byte.

To remove my confusion (raised by your comment on display may just indicate the presence of an OpenTherm thermostat) I did some more testing today - and reality is somewhere in between:
I sent different combinations of the master byte and tested the boiler behavior (draw hot water and creating heating demand - I should have done earlier instead of relying on the display):
0x00 (means: CH & DHW disabled): I was still able to draw hot water;
0x01 (means: CH disabled, & DHW enabled): I was able to draw hot water (not surprising)
0x02 (means: CH enabled, & DHW disabled): CH started working heating up, but I was still able to get hot water
0x03 (means: CH enabled, & DHW enabled): both feature are working
I all cases the slave byte in boiler's reply gave me the right status regarding e.g. flame on or DHW active.

Summary: it seems, I can control CH, but cannot control DHW (regarding enabling/disabling); the display just indicates an active OpenTherm thermostat, but does not show, what it sends.
This is not totally what I expected, but it at least solves my (imagined) problem that monitoring the slave status bits with ID=0 messages would enable CH - even in summer.

Deviating from the installation manual I'm still able to edit the CH flow temperature on the display while CH is active.

So, thanks a lot for your hint.
Uef

[hvxl]

It seems your expectations are a little bit different from the ideas behind the opentherm protocol. The DHW enable bit controls the comfort mode. Setting the DHW enable bit to 0 only switches off the heating of a small water storage tank that may be present in the boiler. It does not completely disable the production of hot water. This is also why the LED setting for showing the DHW enable bit is 'C'; Comfort mode (Domestic Hot Water Enable) is on.

[uef]

Yes, your are right: my assumption was that clearing the DHW bit would disable DHW at all - not just disable heating of this little tank of hot water (btw: I wasn't even aware of this "inside" tank).

Triggered by your post I tested the difference between cold and hot tank but since my bathroom is >12 "tube meters" away from boiler it seems the copper tube more or less fully "eats" the stored energy.
So it doesn't make a difference in time you have to wait before the water in the shower reaches an adaquate temperature.
(this of course changes completely once CH is enabled and keep whole boiler on a permanent temperature level)

So I learned: no DHW bit required for me at least during summer (may be at all).

[hvxl]

In my opinion, the only place you really notice a difference is your gas bill. Having DHW enabled can use 20 to 100 m³ of gas per year. And I heard stories of boilers that even burn significantly more than that amount.