DHW woes... and... Why does the OTGW Lie to the thermostat re: message id 6

[roycruse]

Hi, Im currently in the midst of support tickets to both Tado (My opentherm controller manufacturer) and Navien (My boiler manufacturer) regarding very disappointing communication and compatibility between these 2 units.

unfortunately convincing Tado to escalate my issue to their Dev team is taking time and Navien UK have forwarded all my queries to Korea as its already above their heads...

Anyway I'm taking the time to study and better understand the coms between my thermostat and boiler as it makes me better at explaining to these manufacturers whats wrong with their products.

An OTGW question I have is why does the OTGW lie to the thermostat about the boilers capabilities when the thermostat requests this with a message ID 6 as per the log below

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23:32:23.873242	T00060000	Read-Data 	Remote parameter flags (MsgID=6): 00000000 00000000
23:32:24.044121	BC0060003	Read-Ack  	Remote parameter flags (MsgID=6): 00000000 00000011
		   - DHW setpoint transfer: disabled (0)
		   - max CH setpoint transfer: disabled (0)
		   - DHW setpoint: read/write (1)
		   - max CH setpoint: read/write (1)
23:32:24.059084	AC0060303	Read-Ack  	Remote parameter flags (MsgID=6): 00000011 00000011
		   - DHW setpoint transfer: enabled (1)
		   - max CH setpoint transfer: enabled (1)
		   - DHW setpoint: read/write (1)
		   - max CH setpoint: read/write (1)

What exactly is "DHW setpoint transfer" and "max CH setpoint transfer" and what benefit to the system is there if my thermostat thinks this is enabled when its not ?



One of the main issues Im suffering from is my combi boiler will not Enable the DHW on the boiler so that it wakes up and heats up its internal thermal store ready to provide hot water. I believe the Tado is sending the correct command for this - but the boiler is just stubborn and replies with its not enabled - anything i can do in OTGW to help here or am i back to waiting for a response from Korea... heres the comkmands as sent and recieved.

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23:32:28.366759	T80000200	Read-Data 	Status (MsgID=0): 00000010 00000000
		   - CH enable: disabled (0)
		   - DHW enable: enabled (1)
		   - Cooling enable: disabled (0)
		   - OTC active: not active (0)
		   - CH2 enable: disabled (0)
		   - Summer/winter mode: winter (0)
		   - DHW blocking: unblocked (0)
23:32:28.535550	B40000200	Read-Ack  	Status (MsgID=0): 00000010 00000000
		   - Fault indication: no fault (0)
		   - CH mode: not active (0)
		   - DHW mode: not active (0)
		   - Flame status: flame off (0)
		   - Cooling status: not active (0)
		   - CH2 mode: not active (0)
		   - Diagnostic indication: no diagnostics (0)
		   - Electricity production: not active (0)

Am I right in thinking there is no "Write-Data" command thats needed to turn on DHW Enabled. the opentherm spec seems a bit odd to me that it sends a "Read-Data" status command thats supposed to turn on and off params in the boiler.

[hvxl]

An OTGW question I have is why does the OTGW lie to the thermostat about the boilers capabilities when the thermostat requests this with a message ID 6.

What exactly is "DHW setpoint transfer" and "max CH setpoint transfer" and what benefit to the system is there if my thermostat thinks this is enabled when its not?

The OTGW does not lie about the boiler's capabilities. What it reports to the thermostat in MsgID 6 are its own capabilities. Those may enhance the capabilities of the boiler.

The "DHW setpoint transfer" and "max CH setpoint transfer" bits indicate whether MsgIDs 56 and 57 are supported to access the DHW setpoint and/or max CH setpoint settings. The read/write flags indicate if the parameters are read-only, or if they can be written as well.

In fact, your boiler is reporting a confusing combination of flags: It indicates that it doesn't support the parameters, but they may be written.

One of the main issues Im suffering from is my combi boiler will not Enable the DHW on the boiler so that it wakes up and heats up its internal thermal store ready to provide hot water. I believe the Tado is sending the correct command for this - but the boiler is just stubborn and replies with its not enabled - anything i can do in OTGW to help here or am i back to waiting for a response from Korea...

Am I right in thinking there is no "Write-Data" command thats needed to turn on DHW Enabled. the opentherm spec seems a bit odd to me that it sends a "Read-Data" status command thats supposed to turn on and off params in the boiler.

MsgID 0 is a bit special (along with 70 and 101) in that the high byte writes data to the slave, while the low byte returns data from the slave to the master. So these are neither pure Read nor pure Write commands. Apparently the decision was made to define them as READ-DATA messages.

The DHW enable bit only indicates that the thermostat requests the boiler to keep its water storage tank heated. There is no bit defined for the boiler to confirm this request. So the boiler cannot reply that it is not enabled. When the boiler actually heats the storage tank, it will normally report that via the DHW mode bit, in combination with the Flame status bit. But there may be several legitimate reasons for the boiler not to heat the storage tank when the DHW enable is set:

1. The boiler doesn't have a storage tank.
2. The boiler is in use for central heating.
3. The water in the storage tank is warm enough.
4. The boiler is configured to ECO mode.

The Tado is sending the correct data to request heating of the storage tank, but the response you get from the boiler is not unusual.

[roycruse]

Thanks again for your detailed information.

The boiler is a combi boiler so whilst it does not have a hot water tank - it has a hot water thermal store which is heated to about 75degC - this water is then dumped into a plate heat exchanger to rapidly and instantly heat water on demand as soon as flow is detected on the hot water circuit - the boiler then has time to fire up and get to temperature to maintain hot water demand if your say running a bath.

When ever I manually enable hot water via the boilers front panel controls it fires up and warms up this store ready and keeps it warm by periodically firing up if it cools. But there is no mode on the boiler which hands this control over to Opentherm even though thats what the DHW enable should be doing.

What DHW Enable does do instead is stop the boiler responding to the hot water flow sensor - so when its not enabled turning the tap on does nothing.

Likewise the boiler is also ignoring the opentherm DHW setpoint temperature. when the boiler is not in opentherm control mode you can choose a DHW flow temperature on the front panel. When opentherm is connected this front panel control is locked out and the hot water reverts to 50degC. All opentherm messages to change this are completely ignored.

[hvxl]

When ever I manually enable hot water via the boilers front panel controls it fires up and warms up this store ready and keeps it warm by periodically firing up if it cools. But there is no mode on the boiler which hands this control over to Opentherm even though thats what the DHW enable should be doing.

What DHW Enable does do instead is stop the boiler responding to the hot water flow sensor - so when its not enabled turning the tap on does nothing.

That's just plain wrong. The Opentherm association specifically says the following about DHW enable bit: "The room unit can enable or disable the comfort mode of DHW with this bit. Disabling will only switch off the loading of a small storage tank when present. DHW preparation during actual demand is not disabled."