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D

doitmyself

As the graph shows, boiler gets over the spike only when setpoint temperature goes a little bit over 30 degress.
Can you post a copy of the log? This will show the messages between the uSense and the boiler. Only those sent while the boiler is trying to light are required.
 
OP
V

Valdas

Can you post a copy of the log? This will show the messages between the uSense and the boiler. Only those sent while the boiler is trying to light are required.
Pasting the log which was produced at the time of ignition.
18:09:53.108755 T00000300 Read-Data Status: 00000011 00000000
18:09:53.249320 B40000302 Read-Ack Status: 00000011 00000010
18:09:54.108727 T90011EB3 Write-Data Control setpoint: 30.70
18:09:54.264932 B50011EB3 Write-Ack Control setpoint: 30.70
18:09:55.124474 T00110000 Read-Data Relative modulation level: 0.00
18:09:55.265010 BC0110000 Read-Ack Relative modulation level: 0.00
18:09:56.124454 T80190000 Read-Data Boiler water temperature: 0.00
18:09:56.280670 B40191866 Read-Ack Boiler water temperature: 24.40
18:09:57.124458 T101815D1 Write-Data Room temperature: 21.82
18:09:57.139510 R00740000 Read-Data Burner starts: 0
18:09:57.280680 BC074DEA0 Read-Ack Burner starts: 56992
18:09:57.295408 A701815D1 Unk-DataId Room temperature: 21.82
18:09:58.140062 T00000300 Read-Data Status: 00000011 00000000
18:09:58.280538 B40000302 Read-Ack Status: 00000011 00000010
18:09:59.140078 T90011EB3 Write-Data Control setpoint: 30.70
18:09:59.296146 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:00.155698 T00110000 Read-Data Relative modulation level: 0.00
18:10:00.311794 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:01.155751 T80190000 Read-Data Boiler water temperature: 0.00
18:10:01.327453 B40191866 Read-Ack Boiler water temperature: 24.40
18:10:02.171340 T801A0000 Read-Data DHW temperature: 0.00
18:10:02.327493 B401A3533 Read-Ack DHW temperature: 53.20
18:10:03.171340 T00000300 Read-Data Status: 00000011 00000000
18:10:03.343118 B40000302 Read-Ack Status: 00000011 00000010
18:10:04.186950 T90011EB3 Write-Data Control setpoint: 30.70
18:10:04.343179 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:05.187021 T00110000 Read-Data Relative modulation level: 0.00
18:10:05.358760 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:06.202610 T80190000 Read-Data Boiler water temperature: 0.00
18:10:06.358778 BC0191880 Read-Ack Boiler water temperature: 24.50
18:10:07.202738 T80730000 Read-Data OEM diagnostic code: 0
18:10:07.218018 R00780000 Read-Data Burner operation hours: 0
18:10:07.374399 BC07803D4 Read-Ack Burner operation hours: 980
18:10:07.388754 A70730000 Unk-DataId OEM diagnostic code: 0
18:10:08.218257 T00000300 Read-Data Status: 00000011 00000000
18:10:08.374357 BC000030A Read-Ack Status: 00000011 00001010
18:10:08.546166 T00000300 Read-Data Status: 00000011 00000000
18:10:08.780521 BC000030A Read-Ack Status: 00000011 00001010
18:10:08.952282 T00000300 Read-Data Status: 00000011 00000000
18:10:09.170937 BC000030A Read-Ack Status: 00000011 00001010
18:10:09.874255 T90011EB3 Write-Data Control setpoint: 30.70
18:10:10.077310 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:10.890048 T00110000 Read-Data Relative modulation level: 0.00
18:10:11.093177 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:11.890140 T80190000 Read-Data Boiler water temperature: 0.00
18:10:12.108817 B40191E99 Read-Ack Boiler water temperature: 30.60
18:10:12.905783 T90383200 Write-Data DHW setpoint: 50.00
18:10:13.124419 B50383200 Write-Ack DHW setpoint: 50.00
18:10:13.905831 T00000300 Read-Data Status: 00000011 00000000
18:10:14.124485 BC000030A Read-Ack Status: 00000011 00001010
18:10:14.921466 T90011EB3 Write-Data Control setpoint: 30.70
18:10:15.124534 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:15.921425 T00110000 Read-Data Relative modulation level: 0.00
18:10:16.140124 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:16.937030 T80190000 Read-Data Boiler water temperature: 0.00
18:10:17.140234 BC0192500 Read-Ack Boiler water temperature: 37.00
18:10:17.936982 T00050000 Read-Data Application-specific flags: 00000000 0
18:10:18.155773 BC0050000 Read-Ack Application-specific flags: 00000000 0
18:10:18.937100 T00000300 Read-Data Status: 00000011 00000000
18:10:19.155762 BC000030A Read-Ack Status: 00000011 00001010
18:10:19.952619 T90011EB3 Write-Data Control setpoint: 30.70
18:10:20.171328 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:20.952720 T00110000 Read-Data Relative modulation level: 0.00
18:10:21.171315 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:21.968293 T80190000 Read-Data Boiler water temperature: 0.00
18:10:22.186925 BC0192719 Read-Ack Boiler water temperature: 39.10
18:10:22.968328 T001B0000 Read-Data Outside temperature: 0.00
18:10:23.186957 BC01B054D Read-Ack Outside temperature: 5.30
18:10:23.983924 T00000300 Read-Data Status: 00000011 00000000
18:10:24.202570 B40000302 Read-Ack Status: 00000011 00000010
18:10:24.374378 T00000300 Read-Data Status: 00000011 00000000
18:10:24.702489 B40000302 Read-Ack Status: 00000011 00000010
18:10:24.874279 T00000300 Read-Data Status: 00000011 00000000
18:10:25.202548 B40000302 Read-Ack Status: 00000011 00000010
18:10:25.796222 T90011EB3 Write-Data Control setpoint: 30.70
18:10:25.999309 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:26.796388 T00110000 Read-Data Relative modulation level: 0.00
18:10:27.015029 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:27.812033 T80190000 Read-Data Boiler water temperature: 0.00
18:10:28.015128 B40192380 Read-Ack Boiler water temperature: 35.50
18:10:28.812098 T900E6400 Write-Data Maximum relative modulation level: 100.00
18:10:29.046341 B500E6400 Write-Ack Maximum relative modulation level: 100.00
18:10:29.827707 T00000300 Read-Data Status: 00000011 00000000
18:10:30.046349 B40000302 Read-Ack Status: 00000011 00000010
18:10:30.827740 T90011EB3 Write-Data Control setpoint: 30.70
18:10:31.046393 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:31.843414 T00110000 Read-Data Relative modulation level: 0.00
18:10:32.062006 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:32.843416 T80190000 Read-Data Boiler water temperature: 0.00
18:10:33.062062 B40191CCD Read-Ack Boiler water temperature: 28.80
18:10:33.858917 T90101600 Write-Data Room setpoint: 22.00
18:10:33.874089 R00740000 Read-Data Burner starts: 0
18:10:34.077566 B4074DEA1 Read-Ack Burner starts: 56993
18:10:34.092368 A50101600 Write-Ack Room setpoint: 22.00
18:10:34.858934 T00000300 Read-Data Status: 00000011 00000000
18:10:35.077562 B40000302 Read-Ack Status: 00000011 00000010
18:10:35.874595 T90011EB3 Write-Data Control setpoint: 30.70
18:10:36.093320 B50011EB3 Write-Ack Control setpoint: 30.70
18:10:36.874300 T00110000 Read-Data Relative modulation level: 0.00
18:10:37.092811 BC0110000 Read-Ack Relative modulation level: 0.00
18:10:37.889807 T80190000 Read-Data Boiler water temperature: 0.00
18:10:38.092995 B40191980 Read-Ack Boiler water temperature: 25.50
18:10:38.889975 T101815D1 Write-Data Room temperature: 21.82
18:10:38.905778 R00780000 Read-Data Burner operation hours: 0
18:10:39.108631 BC07803D4 Read-Ack Burner operation hours: 980
18:10:39.123521 A701815D1 Unk-DataId Room temperature: 21.82
 
D

doitmyself

Thanks for the log.

The log shows less than one minute of data, but does not show when the boiler eventually lights. It's impossible to see how long that takes as there is no time information on the graph,

Do you have an external sensor for weather compensated boiler temperature control? The log shows a request for the data and a reply of 5.3C. If so, was it commisioned by the installer so the correct flow temperatures were obtained?

Have you tried our suggestion of disconnecting the thermostat and replacing it with a link? This will then eliminate the boiler or the stat as the cause of your problem.
 
OP
V

Valdas

Thanks for the log.

The log shows less than one minute of data, but does not show when the boiler eventually lights. It's impossible to see how long that takes as there is no time information on the graph,

Do you have an external sensor for weather compensated boiler temperature control? The log shows a request for the data and a reply of 5.3C. If so, was it commisioned by the installer so the correct flow temperatures were obtained?

Have you tried our suggestion of disconnecting the thermostat and replacing it with a link? This will then eliminate the boiler or the stat as the cause of your problem.
The log represents one spike of the graph. As far as I understand Read Status command tells what's happening with the boiler.
Status: 00000011 00000010 - means circulating pump is on, flame is off.
Status: 00000011 00001010 - means circulating pump is on, flame is on.
So according to the log, ignition happened at 18:10:08 and boiler went off 18:10:24. During that time temperature inside boiler rose up from 24.50 C to 39.10C.

Yes, there is a weather compensation control that is adjusted to meet house energy requirements for floor heating.
I will disconnect the thermostat this evening and will tell the difference.
 
D

doitmyself

Status: 00000011 00000010 - means circulating pump is on, flame is off.
Status: 00000011 00001010 - means circulating pump is on, flame is on.
Opentherm has no way of saying if the pump is working or not; this is because the pump is not always controlled by the boiler. Bit 3 (in bold red) indicates the status of the flame (1=on, 0=off), not the pump. Bit 1 (green) just tells you if CH is 'on', i.e available.

monitor.JPG

Looking again at the Monitor, I am thinking that it just doesn't add up.

  1. The room set point is 22.00 but the Room temperature is 22.05. So why does the boiler need to light?
  2. The relative modulation is 0.00 which means the boiler is set to the lowest ouutput. So it can't modulate any lower all it can do is run in on/off mode, which it is doing - initially.
  3. The Control setpoint (required water temperature) is 28.90, but the water temperature is already 33.90. So why does the boiler need to turn on?
The boiler is running in on/off mode, unnecesarily, as the house is already up to temperature. So what happens to make the boiler suddenly decide to ramp up to 100% modulation and start a frenzied dance?

The log from just before the boiler ramps up for a few minutes after may provide a clue. It may be a large file, so zip it up and attach it to your reply.

Second thought: How long have you had the boiler and thermostat?
 
OP
V

Valdas

Opentherm has no way of saying if the pump is working or not; this is because the pump is not always controlled by the boiler. Bit 3 (in bold red) indicates the status of the flame (1=on, 0=off), not the pump. Bit 1 (green) just tells you if CH is 'on', i.e available.

View attachment 43009

Looking again at the Monitor, I am thinking that it just doesn't add up.

  1. The room set point is 22.00 but the Room temperature is 22.05. So why does the boiler need to light?
  2. The relative modulation is 0.00 which means the boiler is set to the lowest ouutput. So it can't modulate any lower all it can do is run in on/off mode, which it is doing - initially.
  3. The Control setpoint (required water temperature) is 28.90, but the water temperature is already 33.90. So why does the boiler need to turn on?
The boiler is running in on/off mode, unnecesarily, as the house is already up to temperature. So what happens to make the boiler suddenly decide to ramp up to 100% modulation and start a frenzied dance?

The log from just before the boiler ramps up for a few minutes after may provide a clue. It may be a large file, so zip it up and attach it to your reply.

Second thought: How long have you had the boiler and thermostat?
Thanks for your reply. I'll try to explain:
1. Probably there is some kind of threshold. Boiler doesn't cut of the flame at the moment room setpoint temperature is reached, it goes on for a little bit more.
2. Header at the top of Monitor window shows current values. The most recent part of the graph at that time is not visible as horizontal scroll bar is moved to the left. So visible part of the graph represents historical values that differ from what's at the top.
3. Threshold again. I was told Viessmann exceeds control setpoint temperature by ~7 degrees before switching off. Also lets water temperature to drop ~7 degrees below control setpoint temperature before switching on.

The boiler is 2 years old. At the beginning there was no thermostat at all, I used to set control setpoint manually. Thermostat installed 3 months ago, I think all was working fine. After some time noticed short cycling.

Attaching log file of full day. Graph depicts interval starting at ~18:00.
 

Attachments

D

doitmyself

There's definitely soething unusual going on.

Did you have the boiler installed? If so, who said you needed a 26kW one?

Did you, or your installer, confirm with Viessmann that your boiler would work correctly with a Weather Compensation Sensor and the Baxi Usense thermostat?

How is the HW controlled? How many motorized valves do you have?

Edit: Did you know that the Usense is designed to be used with a combi boiler?
 
Last edited:
OP
V

Valdas

The boiler was installed by Viessmann installer, the capacity was decided according to the size of house (140 m2) and hot water demand for 2 bathrooms. Installer confirmed that older versions of Baxi/Remeha/De Dietrich OpenTherm thermostats work fine with Vitodens 100-W boilers. Baxi uSense was his first installation with Viessmann.
I adjusted heating curve according to installers comments. These are the values of the curve:

Outside temp - Circuit temperature
-20c - 39c
-15c - 37c
-10c - 35c
-5c - 33c
0c - 31c
5c - 29c
10c - 27c
15c - 25c

House meets "A" energy efficiency class building requirements. Boiler heats separate HW tank(temperature sensor installed) which is fed directly from the mains according to HW temperature sensor. I'm not aware of any motorized valves.
Now I have unplugged Weather compensation sensor and will monitor how the boiler behaves.
 
J

John.g

It seems to me that you found the problem stating in post #11 that the SP has to be > 30C to get the boiler away which indicates that the minimum weather compensated SP temperature should be > 30C, if the SP is say 32C then the boiler shouldn't fire until 25C (SP-7) and must not reach 39C (SP+7) to avoid cut out.
 
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