Valliant Boiler ecotech 832- Heating Partial Load

[Johntheo5]

Yes,correct.


D.17 = - Flow
D.18 = 3 ECO
D.19 = 2

That Auo setting is a mystery to me anyhow as 15% pump speed just cannot IMO circulate anything really, Vaillant might throw some light on it.

If you just use the targettemp as the control for the rad output control then flow/retun temps of 64C/60c will still give 80% rad output but poor boiler efficiency, but once you get down to the following then from 60% rad output down you are in a condensing mode and good boiler efficiency. Generally, 30% to 50% rad output will meet most heating requirements in this part of the world with excellent condensing.
So Flowtemp/returntemp/dT/output
64C/60C/4C/80%
59.7C/56.2C/3.5C/70%
55.3C/52.2C/3.1C/60%
50.6C/48.1C/2.5C/50%
45.8C/43.6C/2.2C/40%
40.6C/39.1C/1.5C/30%

 

[Delta925]

On reading the MIs again, D.171 is not active when the hydraulic (pump) settings are set to 3. temperature spread, dT, so should have no effect in this mode?.

With D.170 set to 3 ( which is dT mode) D.171 is hidden.
To confirm my other settings
D.172 is set to 15
D.173 is set to 100 mbar
D.174 is set to 400mbar
Heating output temperature is set to 60C

The actual pump speed D.15 will be one of the most important readings of all.

As I said above, if you had, which you did, the dT, D.172, set to 15C but only achieving 10C then the pump speed should definitely be down around 40% and should show that in D.15.

A spot check when D.040 output temperature 60C and D.041 return temperature 51C showed D.015 22% and D.029 513 l/hr
D.017 showed flow temperature control.

What do you make of this set from cold startup taken from Data Overview so as the target modulation was available hence flow rate not pump % ?

Based on the boiler being nominally 32kW a target modulation of 36% is 11.5kW and 11% 3.5kW.
Initially target modulation 36% and flow rate fluctuating around 600l/min until the output temperature reached 60C then:

Target Modulation % Flow Rate l/hr Output Temperature degC Return Temperature degC
31 700 61 46
23 660 60 49
16 530 60 51
11 550 58 52
13 540 59 51
14 510 59 51

Initially the flue exhaust was clear but gradually became visible.

 

[Johntheo5]

With D.170 set to 3 ( which is dT mode) D.171 is hidden.
To confirm my other settings
D.172 is set to 15
D.173 is set to 100 mbar
D.174 is set to 400mbar
Heating output temperature is set to 60C


A spot check when D.040 output temperature 60C and D.041 return temperature 51C showed D.015 22% and D.029 513 l/hr
D.017 showed flow temperature control.

What do you make of this set from cold startup taken from Data Overview so as the target modulation was available hence flow rate not pump % ?

Based on the boiler being nominally 32kW a target modulation of 36% is 11.5kW and 11% 3.5kW.
Initially target modulation 36% and flow rate fluctuating around 600l/min until the output temperature reached 60C then:

Target Modulation % Flow Rate l/hr Output Temperature degC Return Temperature degC
31 700 61 46
23 660 60 49
16 530 60 51
11 550 58 52
13 540 59 51
14 510 59 51

Initially the flue exhaust was clear but gradually became visible.

The spot check gives a boiler output of, 513*(60-51)/8660, 5.37kw. If we assume that the by pass is still mixing water at 60C with (by some miracle) rad return water at 45C (dT of15C) then a by pass flow of 3.42LPM at 60C is mixing with 5.13LPM of rad return water at 45C, but unlikely that any water is bypassing at a (IF) pump speed of 22% with a head of ~ 338mbar, 0.33M.

If you take a few more spot checks and the pump speed is apparently very low like above but with the dT no where near 15C then Vaillant should be contacted.

 

[Delta925]

The spot check gives a boiler output of, 513*(60-51)/8660, 5.37kw. If we assume that the by pass is still mixing water at 60C with (by some miracle) rad return water at 45C (dT of15C) then a by pass flow of 3.42LPM at 60C is mixing with 5.13LPM of rad return water at 45C, but unlikely that any water is bypassing at a (IF) pump speed of 22% with a head of ~ 338mbar, 0.33M..

With the feed at around 60C the return in the pipes certainly is not around 45C. I've got probes taped on the pipes in the house before they split to different places. I keep meaning to look for some lagging / wadding to put over them but relatively they show dT is under 10C.

 

[Johntheo5]

Thats evidence enough then, no question about it, I would contact Vaillant ASAP and ask them why the dT control simply isn't working even though the pump speed is allegedly/apparently well down.

Is there any setting in D.170? that allows you to adjust the speed manually?.

 

[Johntheo5]

Spoke to Vaillant Technical this morning, helpful but really couldn't throw any light on the problem but did say D.015, is the actual pump speed.

I would suggest changing to delta P (not sure it thats 2 in D.170??) but take a snaphot as above in dT mode, take a set of readings and try a few different dPs say 400mbar max and 100mbar, minimum and see does d.015 pump speed change and the dT change.

These are the different options, (D.170), which one to use??

0: Without bypass, Δp-const.
1: W/o bypass, Δp-const.,kick
2: Bypass, Δp-const.
3: Spread ΔT
4: Fixed pump stage

Its becoming clearer now, at last! option 2 where you can set the pump head between 100&400mbar is the pump in constant pressure,CP,mode
Option 4 where you can set the pump between 100&400mbar is the pump in constant curve, CC, mode.

D.170 setting Description
2: Bypass, Δp-const.
Constant pressure pump control type
The internal heating pump works in
constant pressure in the heating installation.
The pressure level can be
selected between 100 and 400 mbar
via D.171.
The internal circulation valve is only
opened according to requirements in
order to maintain minimum circulation.
If required, a maximum opening
pressure can be set via D.174.
3: Spread ΔT
Spread pump control type
The internal heating pump works at
a temperature spread between the
flow and return temperature. The target
is the spread level of the heating
system and not the pressure supply.
The target value for the spread
is specified via D.172.
The work area of the heating pump
for the spread regulation can be set
via D.173 and D.174.
4: Fixed pump stage
Pump curve pump control
The internal pump works on a selected
pump curve. The volume flow
and the pressure for the heating
system result via the pump curve
and the system resistance that is
present. The target value for the
pump curve is specified via D.175.
There is no control system for pressure
or temperature; the pump works
on a fixed pump curve.
This pump mode is preferred for
homogeneous heat transfer if a low
loss header, decoupling module,
hydraulic cascading and a buffer
cylinder is installed.
Heating system with radiators
Underfloor heating systems
Heating system

 

[Delta925]

Spoke to Vaillant Technical this morning, helpful but really couldn't throw any light on the problem but did say D.015, is the actual pump speed.

.....

Interesting ....

I will try various modes / setting when the opportunity to log and compare results. This may well not be until around Christmas.

Easy to do is dropping the feed temperature to 55C as set now as this will push deeper into condensing mode with a dT of 8 - 10C. I tried once before but can't recall others settings but then slower to heat up and noticeably less heat output.

Going back over history as supplied / commissioned the mode was dP, D.170 option 2 and I think 200mbar - D.171.
I reduced to 100mbar but then slow to heat up.
The current dT mode as heats up faster.

Also remember the installation is 1970's for a vented system with 22mm feed from the boiler then split in to 15mm for distribution and I still have 1970's radiators - see photo for style.
The lounge always had a Myson fanned convector, without this another radiator would be required. I just changed to a more recent model of nominally the same size that came up on eBay, primarily because the motor to fan couplings were bodged up with silicone sealant so the fan did not run true.

 

[Johntheo5]

So, the saga continues, I have posted a thread "Radiator Temperatures and Outside Air Temperature" which may be of interest and maybe shows that this 20C dT isn't as all important as we are sometimes led to believe?.

 

[Harry Bloomfield]

So, the saga continues, I have posted a thread "Radiator Temperatures and Outside Air Temperature" which may be of interest and maybe shows that this 20C dT isn't as all important as we are sometimes led to believe?.

Here - https://www.diynot.com/diy/threads/radiator-temperatures-and-outside-air-temperatures.637895/