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

 

 

[EinTopaz]

Senior WB technician here with me now. Will update all findings once he’s done and gone but in 5 mins of being here he said that he thinks the HEX is blocked. Based on an inconsistency between what the read out was saying vs what he could feel on one of the internal pipes. Said it may be blocked due to too much inhibitor etc. either way he’s ripped it out and popping a new one in. 
 

Let’s see if it deals with the temperature delta any better! 
 

Also said the target temp should be very close to the flow pipe temp. Within a couple degree and said the previous technicians advice of setting it to 80+ is “incredibly poorly thought out advice” 

 

so I’m glad I’m not going crazy, atleast! 
 

[marshian]

Next question is how did a HEX get blocked in a relatively new system install? 

 

What is the source of the blockage?

 

My concern would be it blocking up again if it is found to be the issue

[EinTopaz]

New HEX in. Flow and boiler LCD within a degree of each other. 
 

[John Carroll]

Great news. Amazed though that there was such a difference with the boiler still outputting 13.6kW and apparently over 20LPM flow.

You might post a set of readings including boiler modulation/output when steady conditions achieved.

[EinTopaz]

Certainly will. The flow pipe has never been hotter than mid 50’s before. I think because I’d gotten used to the rads being 53 ish.  They feel so hot at 60 now.

 

this means I can set the boiler target temp down to 60. So a huge cost saving too I’m sure. 👍

Edited 6 hours ago by EinTopaz

[EinTopaz]

Does anyone know how long it’s supposed to take after reaching target temp before it modulates down?  It’s been at target temp now for 15 mins or so. And only modulated down by a few % 

 

the target and flow pipe stopped rising for those 15 mins but the return pipe still risen

Edited 6 hours ago by EinTopaz

[SimonD]

3 minutes ago, EinTopaz said:

Does anyone know how long it’s supposed to take after reaching target temp before it modulates down?  It’s been at target temp now for 15 mins or so. And only modulated down by a few % 

 

It may very well continue until flow temp starts to increase due to increase in return temperature. As you don't have modulating controls the boiler will modulate only on its internal temps.

 

Glad it got sorted. The behaviour was very interesting.

Edited 6 hours ago by SimonD

[marshian]

1 minute ago, EinTopaz said:

Does anyone know how long it’s supposed to take after reaching target temp before it modulates down?  It’s been at target temp now for 15 mins or so. And only modulated down by a few % 

 

The boiler will be looking at the flow temp and putting in the kW required to keep a steady temp - if it modulated down any more than it is the flow temp would drop

 

Drop the target temp and you'll see it reduce the modulation and then increase it again to maintain the target flow temp.

 

Once the warmer water from the rads start coming back to the boiler - the energy required to maintain the target temp is reduced so at that point it will modulate down further.

 

Till the boiler gets to the point where the temp rises above the target temp and at that point when on min modulation the boiler will allow a certain number of degrees above flow temp before shutting down and waiting for the circuit temp to fall

[John Carroll]

12 minutes ago, EinTopaz said:

Does anyone know how long it’s supposed to take after reaching target temp before it modulates down?  It’s been at target temp now for 15 mins or so. And only modulated down by a few % 

 

the target and flow pipe stopped rising for those 15 mins but the return pipe still risen

Can you just post a set of readings as is, now. Seems mighty strange that its still firing at 100% = 36kW, return temp will tell alot IMO.

Edited 6 hours ago by John Carroll

[EinTopaz]

7 minutes ago, John Carroll said:

Can you just post a set of readings as is, now. Seems mighty strange that its still firing at 100% = 36kW, return temp will tell alot IMO.

It has started to modulate down now. Just very slowly. Maybe it is supposed to be like this and it just seems weird to me now with living with it broken for so long. 
 

Readings

boiler / flow  target 65

boiler / flow actual 66.5

return actual 52.3

burner output 54%

pump output 87%

 

 

Edited 6 hours ago by EinTopaz

[marshian]

Just now, EinTopaz said:

It has started to modulate down now. Just very slowly. Maybe it is supposed to be like this and it just seems weird to me now with living with it broken for so long. 
 

Readings

boiler / flow  target 65

boiler / flow actual 66.5

burner output 54%

pump output 87%

 

 

What's the return temp?

[EinTopaz]

Just now, marshian said:

What's the return temp?

Edited the post 

[marshian]

Just now, EinTopaz said:

Edited the post 

OK seen that now

 

Someone as clever as @John Carroll would probably be able to tell how much kW is being thrown at the circuit based on the flow temp, return temp and flow rate - probably

[John Carroll]

Readings

boiler / flow  target 65

boiler / flow actual 66.5

return actual 52.3

burner output 54%

pump output 87%

 

Strange, but the flowrate has hardly changed from with the old HEX flowrate. 

 

 

 

Edited 5 hours ago by John Carroll

[EinTopaz]

13 minutes ago, John Carroll said:

Readings

boiler / flow  target 65

boiler / flow actual 66.5

return actual 52.3

burner output 54%

pump output 87%

 

Strange, but the flowrate has hardly changed from with the old HEX flowrate. 

 

 

 

What would that suggest for next steps? Certainly the rads are getting hotter than before the HEX was replaced. So that’s good. Wil the rest be down to trying diff pump settings and balancing? 

[marshian]

4 minutes ago, EinTopaz said:

What would that suggest for next steps? Certainly the rads are getting hotter than before the HEX was replaced. So that’s good. Wil the rest be down to trying diff pump settings and balancing? 

 

Depends if you are heating to a schedule or 24/7

 

If heating to a schedule - you really want the boiler to throw whatever kW is needed to bring the house up to temp and you might want the pump to be managed by the boiler.

 

If heating 24/7 - you are just asking the boiler to replace the heat lost (per hour) - in this case range rating (with a margin to allow for extreme temps) and pump speed could be completely different settings wise.

[John Carroll]

 

I suppose so, you can play around with it.

 

It would be interesting to see what the pump modulation goes to and the other data if you remove the minimum clamp.

 

Did the engineer renew anything else apart from the HEX?, you mentioned that he might renew some control card or other??.