The Efficient Home Forum

I have a weird behavior of the DHW. maybe it's some feature I do not know.



I was away from home and my system was set to Away mode. As far as I know the DWH once in AWAY mode is off.

Then the water temp went down as you can see on the graph during the day (date 11/12). However, while the system was still off because I was still away for the day, after midnight the temperature slowly increased bringing my water to around 50 Celsius.

Now I do not get how that is possible while the entire system was scheduled to be off and for the time being, it remained off as far as I konw.

Beside that the way to heat the water was very weird. Usually the hot water is turned on and it is heated in less than 35 minutes. Has the DHW some logic during away mode operation that I'm not aware of?

Interesting thing is that once it got to 50 C (which is not my setpoint. my water setpoint is 55C) it stopped.

I've read here and there that there is a mechanism built in the DHW called freeze protection but i'm not sure how it is related here.

Another thing very weird I've noticed somehow connected w/ what I'm describing here is that the BDR91 which control the heating system was turning on and off every 5 mins as you can see here. green ON and red OFF



Now the setpoint of all the zones during the AWAY mode was set to 18.5C.

Why turning on and off so rapidly?

I have tested my system during normal operation (mode auto - I'm at home) and I've noticed that when the DWH is off and the heating is ON then the water temp drops and the water of the heating system does not go flow into the DWH system so I think that my 3-way valve is fine.

I think the reason of this must be looked in why the controller decided to turn on/off the system every 5 minutes.

Considering also that my mim on time is 4min.

mazzy89 wrote:Another thing very weird I've noticed somehow connected w/ what I'm describing here is that the BDR91 which control the heating system was turning on and off every 5 mins as you can see here. green ON and red OFF



Now the setpoint of all the zones during the AWAY mode was set to 18.5C.

Why turning on and off so rapidly?

This is called 'TPI control'. Google will help you understand this.

mazzy89 wrote:I have tested my system during normal operation (mode auto - I'm at home) and I've noticed that when the DWH is off and the heating is ON then the water temp drops and the water of the heating system does not go flow into the DWH system so I think that my 3-way valve is fine.

I think the reason of this must be looked in why the controller decided to turn on/off the system every 5 minutes.

Considering also that my mim on time is 4min.

3 way valve is probably faulty or wired wrong and going to mid position.