Vaillant ecoTEC Plus 48 - not reaching target temperature

[ericmark]

My question is why would you want it that hot? The whole idea is the cooler the return water is, the more latent heat is extracted, so most boilers turn down the output if the return is too hot.

What can mess up the system is if the radiators have not been balanced correctly, one radiator with the lock shield valves wide open, can result in the boiler reducing output.

Not tried Hive, I use Wiser, but the whole idea is if any room is under temperature, it can fire the boiler, since I use oil, this is a bit different, gas users often have OpenTherm which allows the boiler to run more efficiently. What we aim for is a smooth temperature not a sine wave and that smooth temperature is done by not over heating and radiator or room.

 

[siqveland]

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.

Thank you for all the input.

Yep D.017 has been on 0

I changed the target temperature around. Anything above 60c then D.005 would initially show the set target and within 5-10 seconds of starting the central heating change back down to 60c.

Anything below 60c would stay at the set temp. So when I set it to 55c it stayed at 55c.

I tried playing with D.000 - set at 8kw, 15kw, 20 etc.. made no difference and D.005 would always fall back to 60c very quickly before anything has a chance to fire up and start heating.

I tried changing the pump from auto to 100%, but again made no difference, so I'm not so sure adding and extra pump as Vaillant have suggested, would make any difference.

The boiler only fires up to 75c when the cylinder heating is activated. So if it's only for the cylinder or cylinder & central heating then it goes to 75c. If its only for central heating then it maxes out at 60c.

It's controlled my a simple on/off from the hive so can't think there would any other external temps affecting it.

 

[Johntheo5]

I'm surprised (or maybe not, in view of the ridiculous, IMO, reason they give for this 60C max) that Vaillant didn't change the boiler PCB or at the very least, suggest a factory reset, (D.096 to 1)

I think you should do a few more tests if that way inclined, you can then give them more info.

Ensure all rads, zones etc, open, ensure any roomstats turned up to max.
Set the Target Temp to 50C.
Set D.000 (Partial load) to 30kW.
Set D.014, Pump speed to Auto

After the boiler is running for say 5/7 minutes check
D.040 (flow temp)
D.041 (return temp), (switch between these two as rapidly as possible as a accurate dT is required)
D.015 (actual pump speed, %)
D.029 (Heating flow, LPM)

You can then shut down the boiler as you don't want your house getting too hot.

 

[ScottishGasMan]

Whats the flow rate when its having issues? (D.29)

 

[siqveland]

Just to update,

We fitted a pump to the system and sorted the problem. They suspected the water wasn't able to reach a high enough flow rate the to the pipe diameters.

 

[Johntheo5]

Have you fitted a extra pump to boost the CH flowrate? and if so, what make/model, we (I) allways live and learn, but amazed that it affects the actual parameter D.005 which is a target value if I am intrepeting its description correctly.
Also a bit surprising that any Vaillant boiler with its series beginning with a 4 has a internal pump.

 

[Mottie]

Also a bit surprising that any Vaillant boiler with its series beginning with a 4 has an internal pump.

I don’t think it’s a 4 series, it’s just a 48Kw boiler.

 

[Johntheo5]

I don’t think it’s a 4 series, it’s just a 48Kw boiler.

That makes sense but installing (if) a extra pump or whatever, doesn't. If only say 6 rads were in use then the pipework would surely be OK and I wonder would the target temp, D.005, have still reduced to 60C, but it is what it is.

 

[siqveland]

Supplies 21 rads over 3 floors.

They fitted a grundfos UPS3 pump

 

[Johntheo5]

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


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.

So, they added a (UPS3) extra pump as suggested, above?

 

[siqveland]

So, they added a (UPS3) extra pump as suggested, above?

Yep

 

[Johntheo5]

If inclined to do so, sometime you might note the readings or status of the following when the boiler has been firing for 10/15 minutes or so on CH, of.......
D.028
D.029
D.040
D.041
D.090

 

[ScottishGasMan]

That makes sense but installing (if) a extra pump or whatever, doesn't. If only say 6 rads were in use then the pipework would surely be OK and I wonder would the target temp, D.005, have still reduced to 60C, but it is what it is.

It basically a commercial model (with the output of a large domestic) It needs to be fitted so that it can achieve the correct flow rate which by the sounds of it had no chance of doing on the system in question. If it detects low flow it will limit the max tempreatures and outputs.

 

[Johntheo5]

It basically a commercial model (with the output of a large domestic) It needs to be fitted so that it can achieve the correct flow rate which by the sounds of it had no chance of doing on the system in question. If it detects low flow it will limit the max tempreatures and outputs.

Most if not all boilers base the max required flowrate on a flow/return dT of 20C, if the above boiler is 48kW (on CH) then the required flowrate at this output is 2064LPH, 34.4LPM and while this may basically be a commercial model, it can be range rated to as low as 8kW which only requires a flowrate of 344LPH,5.7LPM, Vaillant surely arn't expecting a flowrate of 34.4LPM at this low output of 8kw which would result in a dT of only 3.3C.
Its a pity we didn't see what the flowrate, D029, was, before installing the UPS3 but at least its still available now.