Short cycling until flow temperature reached - error 2967

[Ccw71]

Hi, I gave PP3 a go. It started off running at about 17 watts and within a few minutes ramped up to 24W. There didn't seem to be any air ingress, but sadly the boiler continued to perform as before. Through all this experimenting, and attempting to get the boiler to run continuously by setting a low max output and flow temp, I've found I can ( with current outside temps) heat the house to my required 19max with a flow temp of 48. But even this low, with the cycling, it's taking well over an hour to reach a steady, non cycling, 48 degree flow!
I've set it back to CP2 as on PP3 there was more power usage, with apparent no benefit?

 

[Johntheo5]

Did you watch the flow temperature from the time it fired up each time while cycling and is status 2967 displayed each ime it cycles?

Had/have you tried it on PP3 at a higher flow temp of say 65C or so to see will it fire continuously from the start?

Edit: The pump should not take minutes to ramp up to its final setting, it should only take 5 secs or less, if it is taking minutes then the boiler will have been firing for almost this long (20 secs less maybe for a prepurge etc) and the flowtemp could well be exceeding SP+5C and leading to burner trip and recycle.
You have it set to CP2 now? so as soon as the pump and boiler start up, it should only take 5 secs or less to ramp up from a start of 12W to 17W (17W was the last value when run in CP2)
Also, of course, the pump should not stop if the boiler is cycling.

Also in PP3 mode it should have started at ony 6W before ramp up.

 

[Ccw71]

Hi, I've run it today with a flow temp of 65 on PP3. I could only fit in 45 minutes, but I've recorded the results, so I'll get them organised tomorrow and post them here. Thanks again.

 

[Ccw71]

TIME​	FLOW​	RETURN​	PUMP W​	STATUS​
00:00:00​	26.9​	16.9​	15​	ON​
01:00:00​	29​	16.9​	16​	​
02:00:00​	32​	17.2​	18​	​
03:00:00​	34.3​	17.7​	20​	​
03:10:00​	34.3​	17.7​	24​	OFF 2967​
05:55:00​	19.4​	18.4​	24​	ON​
07:00:00​	25.5​	18.5​	24​	​
08:00:00​	30.1​	18.9​	23​	​
09:30:00​	37​	19.7​	23​	OFF 2967​
12:20:00​	21.4​	20.5​	24​	ON​
13:00:00​	27​	20.5​	24​	​
14:00:00​	30.5​	20.6​	24​	​
15:00:00​	35​	20.9​	23​	​
16:00:00​	39.2​	21.5​	23​	OFF 2967​
17:00:00​	24.8​	22​	23​	​
18:00:00​	24.4​	22.3​	24​	​
18:50:00​	23.9​	22.3​	24​	ON​
20:00:00​	29.9​	22.3​	24​	​
21:00:00​	35​	22.6​	23​	​
22:00:00​	39.2​	22.9​	23​	​
22:35:00​	41.3​	23.3​	23​	OFF 2967​
23:00:00​	31.6​	23.6​	23​	​
24:00:00​	26.5​	23.9​	24​	​
25:00:00​	25.7​	24.1​	24​	​
25:25:00​	25.7​	24​	24​	ON​
26:00:00​	30.9​	23.9​	24​	​
27:00:00​	34.5​	24.1​	24​	​
28:00:00​	38.7​	24.3​	24​	​
29:00:00​	42.9​	24.7​	23​	​
29:10:00​	43.8​	24.9​	23​	OFF 2967​
31:00:00​	28.1​	25.6​	24​	​
32:00:00​	27.3​	25.5​	23​	ON​
33:00:00​	32.9​	25.5​	23​	​
34:00:00​	37.4​	25.7​	24​	​
35:00:00​	41.9​	25.9​	23​	​
35:50:00​	45.2​	26.4​	23​	OFF 2967​
37:00:00​	30.8​	26.8​	23​	​
38:00:00​	29.2​	27​	23​	​
38:40:00​	28.8​	26.9​	23​	ON​
40:00:00​	36.2​	26.8​	23​	​
41:00:00​	40.3​	27.1​	23​	​
42:00:00​	44.6​	27.3​	24​	​
42:40:00​	46.7​	27.7​	24​	OFF 2967​
44:00:00​	31.5​	28.3​	23​	​
45:00:00​	30.7​	28.3​	23​	​
45:27:00​	30.3​	28.1​	23​	ON​
46:00:00​	35.1​	28.1​	23​	​

 

[Ccw71]

There seems to be a fairly consistent difference in the flow temperature between start / stop increase temps and stop / start decrease temps of around 17 degrees. Is that significant or point to anything?

 

[Johntheo5]

There seems to be a fairly consistent difference in the flow temperature between start / stop increase temps and stop / start decrease temps of around 17 degrees. Is that significant or point to anything? the pump was running in PP3 then once it reached 24W it was pumping 15.33LPM and the average of the boiler output at the end of each run period (cut out on 2967) was 19.3kw.

The significance of that seems to be that the boiler is just replacing the heat emitted by the rads during the off periods. If the pump was on PP3 mode then the flowrate of 15.33LPM, at a average dT of 18.04C gives a boiler output of 19.3kw, close to the 22kw rangerated output of the boiler, wonder would increasing the range rating from 55% to say 75% make any difference.

 

[Ccw71]

graph of temps as the cycle continued over 45 minutes.

I'll give it a go on 75%.

 

[Johntheo5]

More info from your numbers. If the boiler range rated output is 22kw then the rad output averaged 12.45kw

Avg ON Time Mins.	Avg OFF Time Mins.	Avg Cycle Time Mins.
3.68	2.81	6.49
56.6%	43.4%

 

[JonathanM]

I'm interested in this as my uncle has recently had the same boiler installed. I've been reading through the manual I downloaded. It's a bit weird, because they seem to have included lots of options which only apply to the system boiler version of the 8000, such as setting the integral pump speed. But it looks like there is an option 1-b8 where you can see the actual burner modulation percentage in real time. I thought that might be interesting.

 

[Ccw71]

I will certainly check this out. Thanks

 

[JonathanM]

This must be so frustrating, and I think the work you've done measuring all the figures and timings is fascinating. And the analysis by Johntheo5, seems to show in other respects your boiler is behaving as expected.

I was wondering whether there is an option with boilers to do a "factory reset". Don't do it without proper advice from one of the pros on here! But maybe this is a silly little software glitch that might get solved that way.

 

[Johntheo5]

I suppose only for the dreaded 2967 as this is what shuts the burner down then one would wonder why the cycling, then when eventually the flow SP is achieved, all is well. If the range rating is increased to 75% then one would think that the ON time will be much shorter due to increased combustion chamber temperature.

 

[Ccw71]

OK, so here are the next set of observations taken over 1 hour. PP3, FLOW 65, BOILER RATED MAX OP 75%

TIME​	FLOW​	RETURN​	STATUS​
0​	22.3​	15.6​	ON​
1​	24.1​	15.1​	​
2​	29.2​	16.5​	​
3​	32.6​	16.9​	​
03:30​	34​	17.1​	OFF​
4​	24.4​	17.3​	​
5​	19.3​	17.7​	​
6​	18.9​	17.9​	​
06:20​	18.5​	17.9​	ON​
7​	24.2​	17.9​	​
8​	27.8​	18.3​	​
9​	32.3​	18.7​	​
10​	36.4​	19.2​	​
10:05​	37​	19.3​	OFF​
11​	23.2​	19.8​	​
12​	21.8​	20.1​	​
13​	21​	19.9​	ON​
14​	27.4​	20​	​
15​	32.2​	20.3​	​
16​	36.4​	20.7​	​
16:35​	39.1​	21.1​	OFF​
17​	30.7​	21.3​	​
18​	24.2​	21.7​	​
19​	23.4​	22​	​
19:27​	23.4​	21.9​	ON​
20​	28.3​	21.9​	​
21​	31.9​	22.1​	​
22​	36.1​	22.3​	​
23​	40.4​	22.8​	​
23:20​	41.5​	23​	OFF​
24​	29.5​	23.5​	​
25​	25.9​	23.8​	​
26​	25.5​	23.8​	​
26:10​	25.1​	23.8​	ON​
27​	30.6​	23.8​	​
28​	34.9​	23.9​	​
29​	39.1​	24.2​	​
30​	43​	24.6​	​
30:10​	44.1​	24.8​	OFF​
31​	30.4​	25.3​	​
32​	28​	25.5​	​
33​	27.1​	25.4​	ON​
34​	32.8​	25.4​	​
35​	37.5​	25.6​	​
36​	41.3​	25.8​	​
37​	45.6​	26.4​	OFF​
38​	31.4​	26.9​	​
39​	29.5​	27​	​
39:50​	28.7​	26.9​	ON​
41​	35​	26.9​	​
42​	38​	26.9​	​
43​	40.1​	27.1​	​
44​	44​	27.5​	​
45​	47.8​	27.9​	OFF​
46​	33.1​	28.3​	​
47​	31​	28.4​	​
47:50​	30.5​	28.3​	ON​
49​	36.6​	28.3​	​
50​	40.8​	28.5​	​
51​	45.1​	28.7​	​
52​	48.6​	29.3​	OFF​
53​	34.8​	29.6​	​
54​	32.5​	29.8​	​
54:40​	31.7​	29.6​	ON​
56​	37.8​	29.5​	​
57​	42​	29.6​	​
58​	45.9​	29.8​	​
59​	49.5​	30.3​	​
59:10​	50.4​	30.5​	OFF​

 

[Johntheo5]

I will crunch a few numbers later.

Assume OFF is with 2967?

You checked the sensors??, do you know the actual position of the one thats attached to the heat exchanger and are both securely strapped on?.

There's really not alot more you can do IMO, maybe have a chat with the boiler manufacturer.

Maybe worth giving the Hx a back flush as suggest early on even though the flowrates seem identical before/after chemical clean.
Ironicall the chemical clean probably enable greater/quicker transfer to the sensors, whether this is significant or not?.

 

[Johntheo5]

There are some very large differences in the flow temperatures in very short time periods, especially when the burner cuts off, but rise reasonably well when burner on??.
Did you take those (flow) readings from the boiler display??.

I would be inclined to check that flow temp sensor again, possibly renew?



Boiler range rated to 75%, 30kw. Rad Output average 17.67kw

Avg ON Time Mins.	Avg OFF Time Mins.	Avg Cycle Time Mins.
4.04	2.83	6.87
58.9%	41.1%

Boiler range rated to 55%, 22kw. rad output average 12.45kw

Avg ON Time Mins.	Avg OFF Time Mins.	Avg Cycle Time Mins.
3.68	2.81	6.49
56.6%	43.4%