Viessmann vitodens 200 low modulation low run time high return temp

[Johntheo5]

If you can note (or plot) the OT temperature and the flowtemperature at the time the burner trips then you can read the flowtemp SP off the curve and compare it to the trip temperature, if it is the 5C dT thats tripping the burner then maybe open up the rad valve flow contros.

 

[monkeysballs]

Let me fire up the pc as I cant make graphs on the phone easily

Cheers for all this help

Had a shock the first night when we burnt 60kw and spent the night sweating as despite it being set at 18 over night at that point it was over 22c but I was getting burns every couple of minutes

 

[monkeysballs]

there is flow and ot the 2 spikes are showers at 6 and 8:30

 

[monkeysballs]

all valves set to their max now so lets see what happens ( i had put the set temp up to 19 but now im just too hot so ive had to put it down to 18 again

 

[Johntheo5]

Above trend seems to show a temp overshoot of 1C to 2C when OT was 5C (SP 35C, flowtemps 36/37C) and up to 10C when OT was 7.3C (SP 32C, flowtemp 42C) so a bit inconclusive except monitoring is a bit sluggish, a overshoot of 2C/3C should IMO be quite normal and shouldn't cause burner trip.

 

[Deleted member 281264]

I'm having the same issue but with a weather comped Vaillant, flow and return temps at the boiler are nowhere near the DT20

I think as someone said before it's a low temperature system so a totally different way of doing things

Does Viesmann have anticycling mode?

 

[monkeysballs]

quite likely there are minmum time between burns etc

i suppose the biggest issue i have is the modulation why isnt it going really any higher than 23% surly if modulation went up burn time would extend to make up for it i think i have everything back as out of the box now setting wise

 

[Johntheo5]

Have you checked this, the delivered condition is "85" which I presume is 27.2kw, (32*85%).

How many rads are on the system, the boiler will only output the rad demand, if only 7kw then it will only output 7kw.

 

[JonathanM]

i suppose the biggest issue i have is the modulation why isnt it going really any higher than 23% surly if modulation went up burn time would extend to make up for it i think i have everything back as out of the box now setting wise

I'm still not sure whether 23% modulation means 77% output or 23% output? You need to be absolutely certain that you have it the right way round.

It seems a bit coincidental that by far the most common modulation is 23%, which is the same value you have range rated the boiler at.

How are you making these modulation graphs? Are you manually recording the modulation percentage, or is the boiler recording them, or is it an app?

EDIT: Also quite a coincidence that the 95% modulation reading was when somebody was having a shower at 8.30.

 

[Johntheo5]

I would think that it's, Modulation, % Output, range rating only applies to CH so the 95% should mean 28.5kw output or 13.6LPM DHW flow at 40C.

 

[monkeysballs]

Have you checked this, the delivered condition is "85" which I presume is 27.2kw, (32*85%).

How many rads are on the system, the boiler will only output the rad demand, if only 7kw then it will only output 7kw.

View attachment 297309

12 rads on the system
I haven't seen that anywhere !

 

[monkeysballs]

The graphs are being pulled from the vicare web api into homeassistant
Mrs had a bath tonight modulation went to 100% so 100% sounds like no modulation

I've taken off the range rating now rads are all fully open all settings back at default as far as I can tell I've turned the temp down further to 15/17

 

[Johntheo5]

12 rads on the system
I haven't seen that anywhere !

I only gave that as a example, 12 rads, assuming ~1.5kw each at full output should require a boiler output of 18kw at a room temp of 18C so why don't you range rate the boiler to greater than 23%, 7.4kw, ( I see you have). Having said that, the rads with flow/return temps of 35/30C will only output 3.6kw so 23% range rating is fine for those conditions.
I think you said you used 60kwh the first night, this averages 7kw over a 8.5Hr night and would require flow/return temps of 45C/40C to give 7kw and a roomtemp of 18C. This is probably the reason that the boiler had/has no real problems in maintaining its flow temp (of up to 45C) even range rated to 23%, 7.4kw.

 

[monkeysballs]

My heat loss is less than 7kwh at -3c in theory

Since midnight we have used 9.62kw
The coldest room dropped to 18 when I had set it to 17 (8pm switch over to setback) for overnight our bedroom is still 19! We are sweating our bits off ! Viessmann have set the curve to .8 and I've now set my temps to 13/15/16 it's 4.2c out at the moment

 

[monkeysballs]

We are now out all day so let's see what it does with nothing adding to the heat like us TV's pc's