Worcester Bosch Greenstar 8000 System Boiler Issues

[EinTopaz]

25 minutes ago, MrPotts said:

Mine is an older Greenstar 24i which doesn’t have a digital display just the old fashioned dials. FWIW mine is set by the dial to 65c but rarely gets above 60c at the flow pipe, not great accuracy but better then you are experiencing.

I'd be happy enough with that! ha. My CDi upstairs has a difference of jus 1 degree between boiler and flow pipe. Maybe i'm spoiled! 

[EinTopaz]

20 minutes ago, John Carroll said:

 

Just thinking thermodynamically.............

 

We know that your measurements of 54C/45C are correct, I would also be quietly confident that my calulated flowrate of 21.7LPM (based on your data) is correct), if we accept that the actual flow temperature leaving the HEX IS say 70C then there is only one thermodynamic explanation for your measured flowtemp of 54C and that is that there is massive bypassing going on internally for one reason or another where some of return water at 45C is mixing with the water at 70C leaving the HEX. 

By calculation, this means that 21.7LPM return water at 45C is entering the boiler, 13.9LPM (at 45C) is bypassing the HEX, the remaining 7.8LPM at 45C is entering the HEX and leaving at 70C to mix with the bypassing 13.9LPM at 45C to give 21.7LPM at 54C exiting the boiler.

(13.9*45)+(7.8*70)=(21.7*54).

Far fetched?? I wonder.

That was my very first suspicion in all of this. I was most disappointed when I read the boiler does not have an internal bypass. I was hoping i could've just adjusted that and bobs yer uncle.  

But you are right, when you simplify it down, either something is stopping the flow pipe from getting that hot, or the heat is staying in the boiler. As the return pipe certainly isn't hot. So it cant be that its making its way round the system too easily either.

[John Carroll]

A conventional by pass mixes HW with the return water and you would be none the wiser except that the boiler had a return temperature display which would then read and be higher than your return measured temperature, it would not affect the flow temperature whereever its measured.

[EinTopaz]

Just trying to think of other possibilities @John Carroll... could the colder temp in the flow pipe be because cold water is coming from somewhere else? like a faulty filling loop. Just been under the floor to have a look at everything and the filling loop looks to be T'd into the flow pipe. Id have thought they usually go on the return.  Long shot?

I guess if it was letting cold water through i'd see ever increasing pressures? And it'd affect the boiler temperature too?

 

 

[EinTopaz]

Video below from what I saw from being under the subfloor earlier (a great way to spend a Sunday evening... honest). I was hoping to find some sort of valves where the 28mm flow and return pipes divide into the two lots of 22mm. But no joy, its all just copper fixings Teeing off. I could see the filling loop was attached to the flow. But looking at the installation manual, that appears to be correct.....

 

The location of where i filmed this is sort of directly beneath where the boiler is, within a meter of it anyway.
 

 

[John Carroll]

The filling loop can't be the problem even of left open full, it would just lift the boiler relief valve, your flowrate of 21.7LPM while not earthshaking at that high pump head is quite adequate, so suggest wait to see what the engineer comes up with tomorrow, it should be quite interesting.

[marshian]

Brings back memories of the first time I went under my suspended ground floor..........

 

I ended up gathering up all the brick rubble mortar chunks, empty drinks cans and sandwich wrappers and then  section by section sweeping up all the small stuff

 

When I eventually got round to insulating between the floor joists it was a much nicer place to be