Vitodens 100 not reporting flame status on short burns

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Astroturf
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Vitodens 100 not reporting flame status on short burns

Post by Astroturf »

The control PCB of my Vitodens 100 got replaced and I noticed that on short burns the flame status bit is not set anymore. This was not the case with the original PCB. Is this something the OTGW could have an influence on? I'm running an older version of the firmware (4.2.5).

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It should look like this:
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hvxl
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Re: Vitodens 100 not reporting flame status on short burns

Post by hvxl »

The OTGW (mostly) just reports the messages it receives. At least it doesn't mess with the status byte it receives from the boiler.

But you have to understand that the boiler doesn't get to choose what to report. The thermostat needs to ask for the information. If the interval that the thermostat requests MsgID 0 is longer than the time the flame is on, it can be missed.
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Astroturf
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Re: Vitodens 100 not reporting flame status on short burns

Post by Astroturf »

The interval is 4 seconds according to the summary. Can I add MsgID 0 as an AA to speed up the requests?
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Maybe it's also due to the colder weather and the control strategy of the thermostat. The thermostat (Honeywell Round Modulation) does not lower the CS abruptly. I have the same setup on the lower floor in my house. Here the thermostat changes the CS considerably so the heating start & stops immediately (low load control).
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Last edited by Astroturf on Wed Jan 25, 2023 9:15 pm, edited 1 time in total.
hvxl
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Re: Vitodens 100 not reporting flame status on short burns

Post by hvxl »

No, you can't add MsgID 0 as an AA. The firmware uses 0 to indicate an unused slot. Even if it was possible, it wouldn't work correctly because the OTGW would send the message with data bytes of 0. That would send CHenable off to the boiler. Anyway 4 seconds should be frequently enough.

I don't recognize what your graph shows as low load control. But that makes sense because the thermostat is not supposed to do low load control. The boiler has reported ID3:HB4 as 1. This means "Master low-off&pump control function is not allowed". In other words, the boiler will do low load control. However, it's not doing a good job of that.

The graph shows that the water temperature rises very quickly when the boiler starts heating, while the return water temperature stays low. Normally the pump should move the heated water out of the boiler so it will be replaced by the colder returning water. This will normally result in a slowly rising boiler water temperature. Your graph gives the impression that your pump is not able to pump enough water through the system. Maybe the pump is starting to fail, or its speed is set too low. There may also be too much resistance in your heating circuit. If you get that fixed, you won't have such extremely short heating bursts and the problem of not showing the short bursts is no longer relevant. These short bursts are bad for your boiler and your gas bill.
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Re: Vitodens 100 not reporting flame status on short burns

Post by Astroturf »

I forced the master pump control on ID3 (SR=3:65,33) and I get a completely different behaviour from the system. The thermostat is now "hard" controlling the setpoint and the max. relative modulation level. CH bit is now cleared after a heating cycle since the CS is set at 10°C. Previously the pump was running the whole day when the thermostat program was active. The boiler has an old Grundfos pump that consumes around 60W. This will save some electricity already.

I'm not sure the pump is failing, I can hear it running. There is not a lot of control on the pump speed (no external control knob or setting on the boiler). I will check if I can replace it with a more efficient one. The return water temp. is from an external DS18B20 sensor. It is attached on the outside of the return pipe. I guess the values are lower than the actual return water temperature.

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Last edited by Astroturf on Fri Jan 27, 2023 6:48 pm, edited 1 time in total.
hvxl
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Re: Vitodens 100 not reporting flame status on short burns

Post by hvxl »

This proves that the thermostat was listening to the boiler and not doing low-load control when told not to. The new graph looks mostly as I expect from low-load control by the thermostat.

This graph also shows that the boiler is very late in reporting the flame status. The water temperature starts rising long before the flame is reported as on. That doesn't make sense. A flame is needed to heat the water. The short bursts of DHW mode after each heating cycle are also unusual.

With "failing" I didn't mean that the pump is not working at all. Just that it may not be producing the force needed to pump water quickly enough through the system.

Even though this looks like more efficient and generally better control of your heating system, it is not the way the boiler manufacturer intended the boiler to be controlled. It's up to you if you care about that.
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Re: Vitodens 100 not reporting flame status on short burns

Post by Astroturf »

hvxl wrote: Fri Jan 27, 2023 5:51 pm This graph also shows that the boiler is very late in reporting the flame status. The water temperature starts rising long before the flame is reported as on.
It's a "feature" of the new control PCB. I did not have this behaviour with the original PCB in the boiler.
hvxl wrote: Fri Jan 27, 2023 5:51 pm The short bursts of DHW mode after each heating cycle are also unusual.
Could this be the boiler dumping excess heat into the heat plate exchanger to keep it warm (comfort mode)?

Thank you for your valuable insights. I will monitor the new behaviour in the coming days.
Last edited by Astroturf on Fri Jan 27, 2023 7:31 pm, edited 3 times in total.
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