ecoTEC plus 832 - not modulating?

[sayitaintso]

Yes, I meant LPH. Okay, I've changed it all back.

It's a shame that mode doesn't seem to work, as the reasoning behind it makes sense. I'm all for squeezing as much energy out of it as possible.

 

[Johntheo5]

So I've given it 20mins, and it seems to be be behaving itself, as in the FT is as it should be.

S.04 Heating mode: Burner on

D.00 Partial load - Automatic
D.005 Flow temp target value - 45deg
D.014 Target Pump speed - not shown
D.015 Actual Pump speed - 86%
D.017 Flow or return temp control - Flow temperature control
D.018 Pump operating mode - Eco
D.040 Flow temp - 45deg
D.041 Return temp - 37deg

I think you should keep a eye on this boiler as it too does not seem to be performing as I would expect in constant pressure mode.....
D170 set to 2. (Bypass dP constant)
D.171 set to 200mbar (Target pressure level value). which I presume you checked.
don't know how many rads you've got but my 10 rad system flows 15.0LPM @ 3.0M (oil fired boiler with practically no pressure loss through its heat exchange, your Gas fired will lose ~ 2.6M @ 21.5LPM through its heat exchanger and doing a few calcs based on a system loss of 3.0M @ 15.0LPM and 3.0M @ 20.0LPM then the circ pump should have only been running at ~ 62% @ its CP SP of 200mbar, 2.0M, flowrate ~ 10.3LPM, or a max of 65% pump speed, flowrate ~ 12.5LPM, (depending on your system loss)
You noted a pump speed of 86% which means the pump was flowing 14.5LPM @ 3.9M or 16.5LPM @ 3.5M (depending on your system loss) no way near its 200mbar SP.

You could reduce D.171 to 150mbar and maye finally to 100mbar after taking a set of readings, however, because its a combi, this might affect the DHW output, so maybe just look at the pump speed as is on CH, change over to a high DHW demand and see does the pump speed stay the same before doing (if) anything.
These pumps can also be run in fixed speed mode but again don't know if this is overridden in DHW mode.

 

[Johntheo5]

Might also add that the problem 630 boiler (but with a LLH) also runs at a pump speed of 83/86% on CP (D.170, 2) modes set to either 100mbar or 200mbar, (D.171). Calcs show that the pump should run at ~ 51% @ 100mbar and 72% @ 200 mbar, higher than the above, because of the LLH and no system resistance, just the boiler HEX. Vaillant say, in effect, "nothing to see here, boiler working as designed, see your installer". It does perform "perfectly" but only in fixed speed mode, (D.170 4), it also doesn't work in temperature spread mode, (D.170 3) which would be very useful especially if only using UFH as very low return boiler temps could be achieved.

 

[sayitaintso]

It seems that I have a new project to get to grips with - my wife already thinks I'm leaving her for the boiler

What seems to have helped with my initial issue is changing d.000 from auto to 25.5kW, a post on another forum mentioned that the auto function on the Vaillants can be a bit tempermental causing them to not ramp-up properly. The new setting seems to get the temp up reasonable quickly before modulating down. Any potential downsides with this?

 

[Johntheo5]

I've often seen it suggested to be used on combis where the heating max demand may only be say 50% of the HW demand, if it fixes your problem then why not?, don't know what Auto actually means though.

 

[Johntheo5]

The readings below are from another 832 driver on here, the dT control is only achieving 13C, also a indicated flow of 836LPH is suspect, if corrected then should be down around 650LPM.
Again, fixed speed control seems to be fine.

If you are up to it, maybe sometime, do that fixed speed test at 50%, or lower, but don't think it can be driven below this in fixed speed mode.

dT control set to 20C
Modulation: 39% (9.75kw)
Target Flow: 62
Actual Flow: 62
Actual Return: 49
Flow rate: 836 l/hour (12.64kw)…..corrected flow rate 645LPH, using 39% mod (9.75kw)
Pump speed: 35%

Fixed pump stage 50%
Modulation: 32% (8.0kw)
Target Flow: 62
Actual Flow: 62
Actual Return: 48
Flow rate: 505 l/hour 505*(62-48)/860, 8.22kw
Pump speed: 50