ecoTEC plus 832 - not modulating?

[sayitaintso]

Hello,

I have a month-old ecoTEC plus 832. House has a 13 rads.

We have a set FT of 45 degrees, and for the most part, it's been great, and we have a hive thermostat control. It doesn't adjust the FT depending on weather.

Last week I noticed that the actual FT was 28 degrees, and the burner modulation was showing as 20% (one bar out of five). It sat like this for 30 mins. I upped the FT to 65 degrees and nothing changed. The actual FT and the burner modulation stayed as they were. I hard rebooted the boiler and it started to behave itself.

Forward to today:

Heating's been on for 45 minutes (set FT of 45 degrees) and the actual FT has only managed to get to 38 degrees. I upped the set FT to 65 degrees to see what would happen, and over the next 45 minutes, it crawled itself upto an actual FT of 50 degrees. Burner modulation at 40%.

The thermostat was demanding heating throughout this time i.e. it hadn't clicked off.

Hot water works fine.

I previously had a Worcester 280 RSF (nigh-on 30 years old) so I'm not as familiar with the newer boiler ways-of-working.

Have you come across this before, and is it easy to resolve? The installer has said I should contact Vaillant as they guarantee it, if it continues. I'm worried that I've been sold a lemon, and I'm going to have ten years of constant issues.

Thanks.

 

[Johntheo5]

Did you buy the boiler yourself or did the installer?, either way I would have expected the installer in interface with Vaillant.

Is the DHW side OK??

If you can acces the diagnostics, I can suggest a few D settings to check, also the status, S, codes

 

[sayitaintso]

The installer purchased the boiler, I thought that they should do any interfacing too.

Anyway, the DHW appears to be fine, and yes, I can access the diagnostics.

Thanks

 

[Johntheo5]

When the boileris firing for say 5 minutes check for any S parameters first, then check.......
D.00 Partial load
D.005 Flow temp target value
D.014 Target Pump speed
D.015 Actual Pump speed
D.017 Flow or return temp control
D.018 Pump operating mode
D.040 Flow temp
D.041 Return temp

 

[sayitaintso]

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

 

[Johntheo5]

Seems OK for now anyway,

One thing that allways puzzles me with these Vaillant system/combi pumps is that their internal bypass is set by default to open at 250mbar, 2.5bar, At 86% pump speed this = 4.4M closed valve pump head for a 6M circ pump and 5.18M for (if) a 7M pump, so the by pass must be partially open for quite a lot of the time except that the system has very little resistance at high flowrates, or the bypass has been adjusted. You are getting a boiler dT of, 45-37, 8C, it would be interesting to see what the return temp is before it enters the boiler.

Also, I think there is, somewhere, the % "target modulation" which is handy if one wants to see the actual boiler output.

Someone found it here in, I think, in a 832 & a 630
"Once in Installer mode the first menu is ' Data overview '. After selecting this and scrolling through ' Target Modulation ' is shown. When I looked it was 18%." so, on a 32kW boiler, 32*18%, 5.76kW?.

 

[sayitaintso]

I've had a look and it's showing a target modulation of 37%, the FT is set to (and achieving 50deg). Return temp is 43deg.

It does seem to be running okay, unless any of those stats are worrying?

 

[Johntheo5]

What sets the target flowtemp?, is it you, or the Nest, or weather compensation or something else? If the slow warm up occurs again, keep a eye on D.005 Flowtemp Target Value, D.040 Flowtemp (&D041) and the Target Modulation.

The modulation seems a bit high for 13 rads if enough time was allowed to heat up fully, their output, based on 50C/43C flow/return & assuming between 18C & 20C room temps is 45% of their full (T50) rating, the boiler output at 37% modulation is, 32*37%, 11.84kW, whick makes the rated rad outputs, 11.84/0.45, 26.3kW or 2.02kW/rad, seems very high?, apart from that, the boiler is achieving its target temperature.

 

[sayitaintso]

It's me who sets the flow temp - the old boiler didn't have numbers or anything, so I'm trying to figure out what works best - and hoping for some condensing efficiency.

It's a 1906 Vic/Edw house, with 5 beds - does that make any difference?

Just rechecked as house temp has just about been reached (19deg), it's stabilised a bit more and target modulation is now 30%, the FT is set to (and achieving 50deg). Return temp is 45deg.

 

[Johntheo5]

Any return temp from 45C or less means more condensing and higher boiler efficiency so on the right track, condensing only begins at ~ 55C according to the graph.

 

[Johntheo5]

You should have the latest model 832, check below that you have by looking for D.170 Hydraulic Operating Mode.
If so, and because these boilers are dispatched/installed with the pump in constant pressure mode, check....
D170 set to 2. (Bypass dP constant)
D.171 set to 200mbar (Target pressure level value).

There is also a very useful setting which will ensure further condensing at the same boiler output,
its called spread dT which is the difference, dT, between the flow & return temps, its settable between 10C and 20C in D.172.
Your last flow/return showed 50C/43C which is a mean rad temperature of, (50+43)/2, 46.5C
If you change D.170 to 3 (Spread dT) and set
D.172 to 19C (Target spread value) and set
D.005? (Target flow temp) to 56C
then the flow/return temps should settle at 56C/37C, dT 19C, to give the same mean temp of (56+37)/2, 46.5C so same rad/boiler output but a nice gain in the condensing effect as the return temp is/should be 37C vs 43C.
You can allways return the settings to the original defaults.

You might (if you do opt for the above) take a set of readings before and after changing but additionally, in both cases, also note D.029 (Heating flow rate LPH.)

 

[sayitaintso]

Thanks - I made the changes and it didn't seem to affect it. The pump stayed at about 1100rpm, and it was flowing at 56/46C.

I've double checked and everything is set as you recommend. Could there be something overriding it?

 

[Why Not Indeed]

I am a bit puzzled by this thread, the title says "not modulating" yet your subsequent posts imply that it is modulating.

Heating's been on for 45 minutes (set FT of 45 degrees) and the actual FT has only managed to get to 38 degrees.

How are you measuring this? When I was measuring mine the flow pipe [about 50cm away] was always cooler than what the boiler reported, but probably not by 7°. Although this was a DS18B20 sensor, cable tied to the pipe and covered with a bit of pipe lagging, so not actually in the flow.

 

[sayitaintso]

Sorry, that's why I had the question mark; in my head, i thought it would go gung-ho when first turned on, then modulate down once temp has been reached, but it seems to just stick at a partial setting for longer. I was very used to an old boiler, that had timer for on/off, and a dial for flow temp (no temp numbers), so this is all a bit new to me.

The temps are just what it says on the boiler display - I don't have any pipe sensors etc.

 

[Johntheo5]

Thanks - I made the changes and it didn't seem to affect it. The pump stayed at about 1100rpm, and it was flowing at 56/46C.

I've double checked and everything is set as you recommend. Could there be something overriding it?

I think Vaillant have a big problem/challenge in getting the temperature spread mode working properly, I had a number of chats with them over a 630 that wasn't/isn't working in either constant pressure or temperature spread mode, all to no avail. Your dT did increase from 7C to 10C but no where near the requested 19C.

OK then, can you, if not allready done so, change back to constant pressure mode...
D.170 to 2 (constant dP) and....
D.171 to 400mbar
when finished, return D.171 to 200mbar or to its original setting.

Just check the pump speed, %, and flow rate, LPH, presume the 1100rpm above should read 1100LPH?, if so, then the rad/boiler output was outputting....
1100*(56-46)/860, 12.79kW, which seems reasonable enough as this flowrate is probably derived from the pump power.