Viessmann Vitodens 200-W B2HA heating issue

[kgfx_5]

When DHWP off then all the water into the boiler flows via the 4M Wilo pump, I can't find a curve for the C2 setting but it looks very much as if the flowrate isn't much more than 1 m3/hr, next time its running can you turn the setting knob to the right until its flashing say 2M then stop and read off the power, W, adjust it then until the power is the same as it was on C2, note the head and return it to C2, I have the pump curves for the CP (constant pressure) settings.

Max flow rate of this pump is 2.7 m3/h, according to manufacturer.. On 2 m. it shows 16 W. When turned fully to the right (4 M.) it shows 20 W.

 

[John.g]

This should mean IMO that the flowrate through the boiler is 1.0 m3/hr, 16.7LPM, so if the boiler has its own internal pump capable of pumping far more, the flowrate is being throttled/controlled by this relatively small pump, running the pump on full CP mode (knob fully right) or setting it to C3 should give ~ 1.4m3/hr at 4M head & 20W which may help the boiler fire up for longer than 11 secs and not reach SP+5C for a few minutes depending on the heating load.
Post 26 showed a dT of , 53-38, 15C, if the primary flowrate is consistent at 1m3/hr, 16.7LPM, then the boiler output was 17.5kw but if it was only just above minimum of say 12kw then the flowrate was only 11.5LPM?.
Another way of checking the primry flowrate is to take the dT and read off the % firing like in post 30 where 19% was presumably the boiler output then, 9.3kw??.
Also, if 16.7LPM is the flowrate through the boiler then the output at a dT of 20C is only 23.3kw, I think the max design flowrate through boilers is based on this 20C dT which means one should be able to circulate 35.1LPM, 2.1m3/hr.

What exactly I wonder is the role of the LLH in your setup as I thought that the primary side dealt with the heat source and the secondary side with the heating demand, the output from the boiler flow is teed off to the heating before the primary (as well as feeding it).
Are there any (other pumps) associated (apart from the UFH manifold pump) with the LLH secondary side?,

 

[kgfx_5]

Are there any (other pumps) associated (apart from the UFH manifold pump) with the LLH secondary side?,

Yes, you can see it in the last picture out of 4. It pumps hot water from the boiler to the system. It is a 40 W max and was always set to 40 W. Here is a sticker. This pump turns off only when DHW pump (lower left) is turned on to add water to cylinder. I have also tried to upload a short video of my system, maybe it would make it easier to understand.

 

[John.g]

Making a bit of sense now.
Looks as if the secondary circulation is way higher than the primary circulation, if you want to get the maximum boiler flowrate then I can't see that being achieved with that 4M pump.
Another test or two if you don't mind.
Confirm 6M pump on C3, if so and because the pump is running at max power it could be circulating anywhere between 1m3/hr and (very unlikely) up to 3m3/hr so can you turn the selector knob clockwise to the right of C3 and stop a few times until you get ~ 30/35 watts, then read off the head and the watts and the flowrate can again be derived, switch it back to C3?? when finished.

Have you confirmed that you have a system boiler with a internal pump?.

 

[kgfx_5]

Have you confirmed that you have a system boiler with a internal pump?

I just looked through old emails, where I have spoken with a salesman, and I have found that he actually wrote “This boiler does not have circulation pump”. Well..

—

3 M is 29 W
3.3 M is 34 W

 

[John.g]

You are probably circulating/recirculating~ 1.7m3/hr.

Why dont you swap the 6M DHW pump with the 4M (if flange distances same), PDHW generally raises the boiler temp to 80C and the 4M pump may/should be quite adequate when circulating through the cylinder coil?, maybe they were installed incorrectly originally?

I would suggest putting the 4m on C3 or maybe max CP setting for now, whichever uses highest power.

 

[kgfx_5]

You are probably circulating/recirculating~ 1.7m3/hr.

Why dont you swap the 6M DHW pump with the 4M (if flange distances same), PDHW generally raises the boiler temp to 80C and the 4M pump may/should be quite adequate when circulating through the cylinder coil?, maybe they were installed incorrectly originally?

I would suggest putting the 4m on C3 or maybe max CP setting for now, whichever uses highest power.

I will call my plumber tomorrow, I don’t think this is a job to diy. Thank you. Do you think it can help with a lower flow temperatures, sub 50C I mean? Or is this a problem because of bad modulation, not flow?

 

[John.g]

It's a combination of both, the boiler fires at a far greater output than its minimum output, yours may be say 30kw, with your present flowrate of 16.7LPM the dT through the boiler will be 25.7C the boiler temp at fireplace is 28/30Csay30C so the flow temp will be 55.7C if the SP temp is 56C then the boiler will stay firing until it reaches 61C. If the flowrate is/can be increased to say 22LPM then the dT will be 19.5C and the flow temp will be 49.5C so the SP can be reduced to 50C, the boiler run time then depends on how fast it modulates to its minimum output and tha actual heating load. As I stared somewhere above you might be able to see the boiler % power on startup in one of the displays above.

 

[John.g]

I will call my plumber tomorrow, I don’t think this is a job to diy. Thank you. Do you think it can help with a lower flow temperatures, sub 50C I mean? Or is this a problem because of bad modulation, not flow?

You should get a fairly substantial increase in boiler flow if you change the 4M pump to C3 or turn the control knob fully clockwise.

 

[John.g]

Does the arrowed pipe supply the HW cylinder coil?.

 

[kgfx_5]

Does the arrowed pipe supply the HW cylinder coil?.

I don’t think so… Not sure though. I think lower pipe (with 6M pump) is for supply.

 

[John.g]

When I follow it in your excellent video it turns left and might be entering the flow (top) of the cylinder coil, the pump is taking it from the coil return and pumping it through the boiler.