Short cycling until flow temperature reached - error 2967

[Johntheo5]

Here are a few numbers/trend etc from above.
The mean rad temp over that 60 minute period was 28.42C, assuming a room temp of 15C gives a rad output of 18% of max rated output, don't know how many rads on the system but assuming 25kw then the rads output was, 25X18%, 4.5kw so whatever way one looks at it, the boiler seems to have been producing very little power while cycling.

 

[JonathanM]

Here are a few numbers/trend etc from above.
The mean rad temp over that 60 minute period was 28.42C, assuming a room temp of 15C gives a rad output of 18% of max rated output, don't know how many rads on the system but assuming 25kw then the rads output was, 25X18%, 4.5kw so whatever way one looks at it, the boiler seems to have been producing very little power while cycling.

Does that output compare with the output you calculated from dT and flow speed?

EDIT: The OP said 15 radiators earlier in the thread.

 

[Johntheo5]

The average of all the flow temps was 33.11C, the average of the returns was 23.72C which gives a mean rad temp of 28.4C, I assumed a room temp of 15C so the rad(s) was a 13.4 deg rad, output = (13.4/50)^1.3, 18.1%.
15 rads at 1.5kw each is almost 23kw rounded up to 25kw, good enough for estimation?.

 

[Johntheo5]

Does that output compare with the output you calculated from dT and flow speed?

EDIT: The OP said 15 radiators earlier in the thread.

The average flow minus the average return, 33.11-23.72 = 9.39C
.Flow approx 15LPM
Kw = 15x60x9.39/860 ,= 9.83.
This would suggest a rated rad output, 9.93/18%, 55kw, most unlikely but the actual room temperature if it was higher than 15C would have a huge reducing effect on the rads output%.

 

[JonathanM]

The average flow minus the average return, 33.11-23.72 = 9.39C
.Flow approx 15LPM
Kw = 15x60x9.39/860 ,= 9.83.
This would suggest a rated rad output, 9.93/18%, 55kw, most unlikely but the actual room temperature if it was higher than 15C would have a huge reducing effect on the rads output%.

If you multiply the 9.83 by the % ON time (56.6%) would that show anything useful?
9.83X 56.6% = 5.56

 

[Johntheo5]

Very difficult to say but would probably think that 9.83kw average is the more likely. At the end of the day action in one form or another is required, its quite strange IMO that a 40kw boiler range rated to 22kw will run quite normally once it reaches its SP but will flag a 2967 error otherwise. It would be nice to know what are the actual numbers etc that flag the code "Temperature differential between flow temperature sensor and heat exchanger temperature limiter is too great"
Might be worth backflushing the Hx even though all pump indications are that its not a flow problem bearing in mind that originally the pump ran in PP2 mode at 9 watts which was a flow rate of 9.8LPM at a 2M head.

This seems to indicate that a boiler reset is required each time??

2967 B

This means the flow / heat exchanger temperature sensor differential is too great.

Try to reset your boiler. You can do this by turning the control knob anti-clockwise to reset the position. If the issue persists then contact Worcester Bosch or BOXT for an engineer call out.

Maybe contact Worcester Bosch and they might give a fixed price for repairs??

 

[DP]

I recently ran X400 around the system

How did you thereafter flush the system.

 

[DP]

You might just get away without air ingress, if required, by running in PP3 mode as the head will be 3.9M but will give a flow of 15.7LPM.
View attachment 281966

Original setting, one year ago, was PP2 which gave a flow of 10/11LPM, Present flow is very close, at 11.2LPM so unlikely to be restricted flow caused by chemical clean?.
View attachment 281967

You should start a course or info page in CC.
Or even here. would certainly be an eye opener and educational. Often the info you regularly present is beyond the installation or repair stage and is never probed or requested but I feel makes a heating engineer a better operator
I would be the first one to sign on.

 

[Ccw71]

HI, sorry for the silence on all the helpful posts. Family duties sometime prevent me from accessing a computer.

@DP I was running X400 through the system with a Magnacleanse attached. I only got about a coffee mug full of magnetite. I was expecting worse. I then opened both 2 port valves, drained down from a drain point below the floor and from the magnaleanse until nothing left. I then left open the drain for about 2 hours with the fill running in the F&E tank. I then shut the drain, bleed the rads, ran pump on high speed to eliminate air from the pump. Later, suspecting an airlock I did a lot of rad bleeding (no air) and cracked the nuts on the pump and the two port valves (also no air)

I totally agree with your comments regarding Johntheo5. His knowledge is extraordinary, as is his generosity to share it and help others.

 

[Ccw71]

I really couldn't say what output the radiators are capable of as they are the original ones from the 70's and vary wildly in size, 2800x400 double to 1200x500 single to a 3000x700 single!

I did take the flow temps from the boilers display. The flow temp sensor (part 19) is strapped to the pipe, close to where it exits the HX. It is in good contact and the resistance is in the correct range. I measure changing resistance when I held the pipe near the sensor, so it appears to be making good contact with the pipe. The HX sensor can be see in the attachment, part 7.

 

[JonathanM]

I did take the flow temps from the boilers display. The flow temp sensor (part 19) is strapped to the pipe, close to where it exits the HX. It is in good contact and the resistance is in the correct range. I measure changing resistance when I held the pipe near the sensor, so it appears to be making good contact with the pipe. The HX sensor can be see in the attachment, part 7.

I know this should be obvious to me - but is the fault that the heat exchanger sensor is reading too high compared with the flow temp sensor - and that difference hits its limit, which trips the boiler?

 

[Ccw71]

That is what the 2967 error code indicates. The big question is why? To summarise - Initial thought's were an airlock or a blockage in the flow of the system. However, as the same error occurs whether the boiler is heating the radiators only OR DHW cylinder only, I believe this eliminates any blockage in the heating system past the two port valve. Could it be a blockage then in the HX....Johntheo5's comprehensive calculations based on temps and pump power in Watts, appear to show there is a good flow of about 15LPM around the system and through the boiler.

 

[Ccw71]

Temperature measurements taken using a Braun Thermoscan against a piece of black tape attached to the flow pipe next to the flow temperature sensor give readings within 1 degree of the boilers displayed current flow temp. So it appear the flow temperature sensor is reading correctly.

 

[Johntheo5]

But, as post #71, what about the Hx sensor check??

 

[JonathanM]

Something which seems a bit odd, is that at 75%, it's taking a bit longer than at 55%, to reach the same flow temperature.

e.g. if you look at the second ON to second OFF on each series, or fifth ON to fifth OFF