Vaillant ecoTEC Plus 48 - not reaching target temperature

[siqveland]

Hi,

I have recently had a Vaillant ecoTEC Plus 48 boiler fitted on the recommendations of the installer and unfortunately have problems with the boiler reaching target temperature for the central heating.

It is set up with 22 radiators and an unvented cylinder in a S plan with a hive thermostat controlling on/off.

Target temperature has been set at 75c and for heating the unvented cylinder this is reached quickly and seems to work well. However when calling on the central heating the boiler struggles to go above 50 - 55c.

I have noticed that in the diagnostics D.005 changes from 75c to 60c when the central heating is called on but it stays at 75c when the unvented cylinder is being heated. Not sure why this would happen they are both being controlled by the same hive input.

Any help would be greatly appreciated.

 

[Mottie]

Can you turn the radiator water temperature up? Is this any help? P.S. I’m not a heating engineer though!

Failing that, get the engineer back that recommended and fitted it and get them to adjust the heating flow temperature.

 

[siqveland]

Yep, the target temperature has been set to 75c but the boiler only gets to around 50-55c when the central heating is running.

If I check the diagnostic codes D.005 shows the target flow temperature. This shows 75c and stays at 75c when heating the cylinder but changes down to 60c when the central heating is turned on.

 

[Mottie]

What about setting the maximum boiler output? My heat only Vaillant is 18Kw. I normally only have it set at 15Kw in the winter and 12Kw in the summer. I find the auto setting no good. I have to enter the installer mode to do that. It’s 17 on Vaillant boilers.

 

[siqveland]

I tried that too but unfortunately doesn't seem to help

 

[DP]

48kW
Does your house need all that power?

 

[Elkato531]

As I remember, the default anti cycle time on these is 20 minutes. What happens is that the boiler fires up and produces a rapid temp rise and shuts down. It then waits 20 minutes and repeats. Can't remember the parameter to change but its in the manual. Try reducing to 5 minutes combined with dropping the heating part load to about 18kw or less.

 

[siqveland]

I just went along with the installers recommendation, but I'm guessing that it is over powered for my setup.

I'll try adjusting the anticycle time and set the partial load, but I don't think it's cycling off/on.

It seems to come on at low power and just maintains a low power output with a temp range of around 50c.

What I found strange is that the target temperature changes itself from 75c to 60c when the central heating is called on and when it is turned off the target temperature changes back to 75c.

 

[Johntheo5]

Yep, the target temperature has been set to 75c but the boiler only gets to around 50-55c when the central heating is running.

If I check the diagnostic codes D.005 shows the target flow temperature. This shows 75c and stays at 75c when heating the cylinder but changes down to 60c when the central heating is turned on.

Have you checked D.071 isn't set to 60C?, .....Target Value maximum Heating Flow temp, 30C to 80C, default 75C
also that D.017 is set to 0, (Flow temperature control).

 

[siqveland]

Yep D.071 is set to 75c and D.017 is set to 0.

D.005 shows target temperature is 75c but when central heating is called this drops down to 60c. The boiler seems to be automatically limiting the heat out put for some reason.

 

[Johntheo5]

Set D.071 to say 50C and see if D.005 then goes to 50C, also what about this "E bus limitations"

 

[Mister Banks]

It’s probably just modulating down as it doesn’t need to provide maximum heat. My rubbish Worcester Bosch is the same, it rarely gets to the set flow of 65c and generally stays below 55c.

 

[Elkato531]

Any weather compensation fitted? This would provide a lower flow temp when external temperature is higher.

 

[siqveland]

Unfortunately these suggestions didn't work.

The installer contacted Vaillant and came back out to re-check the system.

They reckon it's due to the size and length of pipe runs.
The boiler has 28mm output and our system has 22mm pipe running throughout the property with 15mm branches to the rads. The heat isn't getting out of the boiler/pipes quickly enough so it's limiting the temperature down to protect the boiler.

They have suggested either changing some of the pipes or adding an extra pump onto the system a few meters from the boiler but they're not sure this will work.

Not sure if it's worth the hassle trying this or if the boiler is over specced and should have been a smaller one fitted..

 

[Johntheo5]

I don't think that Vaillant explanation is creditable.

Firstly, you say that when CH is selected that D.005 (Target temp) changes from 75C to 60C, so maybe this boiler is so clever that without even attempting to run at 75C that it "knows" that it can only run at 60C, remarkable to say the least, something is definitely triggering this, maybe a phantom weather compensation curve?.
Normally, once the flow temperature exceeds the target temp by 5C then the boiler goes to recycle and will then refire after the recycle time has elapsed and if the flow temperature again exceeds the target temp+5C before modulating then it can recycle repeatedly.

I think I've asked before, check D.017 set to 0, (Flow control)

Also suggest setting the target temp to say 55C and see does d.005 reflect this.
also set D.000, max heating output, to its minimum, probably around 8.5kW, this will not prevent the boiler from firing at ~ 31kW for around 60 secs but if the CH/rads are cold should help to get the boiler away at the very least, you can then increase this incrementally.