What are central heating and domestic central water modes?

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noether
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What are central heating and domestic central water modes?

Post by noether »

Hi,

I recently to start using the OTG quite successfully and now I am looking at the system in more detail. In particular I would like to know
what are the central heating and domestic central water modes. I see that both are enabled in the status so I can choose both modes, but I do not know
what they exactly mean or do.

Thanks in advance.
hvxl
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Re: What are central heating and domestic central water modes?

Post by hvxl »

The central heating mode and domestic hot water mode are bits returned by the boiler to indicate when it is heating tap water or the water in the central heating system. Some thermostats provide an indication for these situations. For example, the Honeywell Chronotherm Modulations shows a tap icon when the domestic hot water mode is on and a radiator icon when the central heating mode is on.
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noether
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Re: What are central heating and domestic central water modes?

Post by noether »

Thanks for the explanation.

I have checked that indeed when I am using the hot water from the tap, the "domestic hot water is on".

I do not understand what is the "flame" indicating then. Sometimes I have the "central heating system on" but the flame is not on. Does it mean that my boiler can heat water by other means than using gas?
hvxl
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Re: What are central heating and domestic central water modes?

Post by hvxl »

You got me there. My understanding is that the thermostat uses the CH enable bit to indicate a heating request. The boiler confirms this by setting the CH mode bit. In some situations the boiler may not set the CH mode bit, most frequently because there is a demand for hot tap water at the same time.

When the boiler does accept the request (and sets the CH mode bit), it will perform some checks based on which it will actually switch the flame on or not. One of those checks may be that the control setpoint is sufficiently above the temperature of the water in the system. If it is not, the boiler does not fire up (and may indicate a problem condition if that situation persists for some length of time).
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noether
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Re: What are central heating and domestic central water modes?

Post by noether »

Thanks a lot for your time trying to clarify this doubt.

To be honest, I find this protocol a little bit with nonsense sometimes, specially when I am reading the .pdf posted in the web I have found that many things have not been defined properly or not defined at all.

Maybe there exist another additional documentation?
emmeesse68
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Re: What are central heating and domestic central water modes?

Post by emmeesse68 »

noether wrote: I do not understand what is the "flame" indicating then. Sometimes I have the "central heating system on" but the flame is not on. Does it mean that my boiler can heat water by other means than using gas?
My boiler sometimes shows CH flag on but flame off. As I observe, expecially now that the outside temperature is getting milder and less heat is required to reach desired temperature, this occurs when my boiler is circulating water without heating it (because it's already warm enough). As soon as CH water temperature drops below a certain level (close but not necessairly identical to the control setpoint at that moment), my boiler fires up. Maybe not all boilers behave the same way but mine seems clear about this...

And this happens with DHW as well, as I just checked by opening hot water just enough to fire the flame. When the DHW reached a certain temperature (strangely, significantly higher than the intended DHW setpoint), the flame went off (I can tell because my boiler is in my kitchen and it's pretty noisy). Flame status flag went off accordingly.

By doing so, I actually caused a boiler fault (it detected a circulation fault, that's strange in DHW function). Anyway, after a few minutes the boiler itself resumed but OTGW didn't. OTMonitor stood still showing fault flag and code, and no messages from my thermostat nor from my boiler, while they were appearently still communicating to one another (thanks to the OTGW failsafe design, I assume). Now I restarted my OTGW (pulled the plug...) and everything went back to normal, but I guess it wasn't OTMonitor to be stuck, because I tried to issue a few GW=R commands from a remote GUI to try resetting the OTGW hardware (unsuccessfully) and I found them in the logs. I think I'll go back designing some way to reset my OTGW remotely, as I was thinking a few days ago...
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