Bypass valve

ok thanks for that. In simple man maths

Johntheo5 said:

1Kwh = 860 kcal and there are 60 minutes in a hour. (860 = 3,600,000/4186)
Some use a very long winded formula but I've used this for over 60 years since my introduction to SI units.
So, kWh = LPM*60*dT/860 or any variation of this. ( I get mixed up in the lower/upper case of the units but the calc is fine), its actually kgs of water but a litre of water is generally taken a being 1 kg.
It can also be used say to calculate the energy required to heat a "tank" of water + time taken to achieve this with a heating element or coil, for example, energy required to heat a 200L cylinder of water from 10C to 60C = 200*(60-10)/860, 11.628 kWh.
(The long winded calc is, 200*4186*(60-10)/3,600.000.)
A 15kW heating coil or element will take,11.628/15, 0.775 hrs, 46.5 minutes.

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ok thanks for that. In simple man maths.... if I want to further increase the pump speed from what i've currently got set. I need to buy an external pump capable of more than 700mbar? Do Grundfos ones do larger pumps than this? I presume it'd be best to fit one of those and dial this internal one down instead?

GeddyMortgage said:

ok thanks for that. In simple man maths


ok thanks for that. In simple man maths.... if I want to further increase the pump speed from what i've currently got set. I need to buy an external pump capable of more than 700mbar? Do Grundfos ones do larger pumps than this? I presume it'd be best to fit one of those and dial this internal one down instead?

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Not good to have pumps in series.
Better to have an LLH, plate or CCTs.

As above, the "normal" way of increasing the effective pump head is to install a LLH (Low Loss Header), where the boiler HEX head losses only are dealth with by the boiler circ pump and the rad/system (secondary) loss are dealth with by another pump. I don't really see though why a a pump in series shouldn't work, I installed one (in series) years ago on someone's system, it was a 6M Wilo Yonos Pico, like my own, where I was able to match the flowrates from each because the Pico has almost infinite CP (&PP) control in 0.1M steps.
The existing pump is a giant of a pump (effecively at least a 10M or more) as it can still pump 1000 LPH (16.7LPM) @ 7.3M and since most boiler manufacturers base the required flowrate at a dT of 20C, in your case, 36kW, requires 25.8LPM, 1548LPH, so 1548LPH @ ~ 6.3M. If the HEX loss at this flowrate is say 2M (200mb) then a residual head of 4.3M (430mB) still available for the system.

I would contact WB and ask them what the boiler HEX loss is, and at what flowrate, it may be given in your MIs.

What exactly is the problem(s) now that you are running the pump at that very high head, is it still just a slow warm up?.

This graph is possibly a good indication of the pressure loss.

Its ~ 2.7M at 1550LPH so even at this very high flowrate the residual pump head at 100% speed is, (assuming a clean HEX), 6.3-2.7, 3.6M, 360mB, probably a bit on the low side but your system doesn't remotely require these flowrates, say at 55.6% boiler output, 20kW, the flowrate required at a dT of 15C is 19.1LPM, 1147LPH with a HEX pressure loss of only 1.47M, residual head of 6.6-1.47, 5.13M, 513mB, if you are still getting problems at this qute high pump head then LLHs or booster pumps are not the answer, the problem lies somewhere else.

Update on this one @Johntheo5 @Madrab and any other people interested.

Still having an issue with this WB Greenstar 8000 life system boiler where the LCD display read out is showing a good 15-20' hotter than the read out at the flow pipe and the rest of the system. The flow pipe gets hottest at 53 or so, this is when the boiler target temp is set to 70. The boiler makes it to 70 within 10mins, it takes maybe 30mins for the flow pipe to get to 53 then it won't go any higher.

In not being able to diagnose why, I had a plumber out who took a look at the pipework and the system design, said all fine and said very unlikely due to a blockage, also serviced the boiler whilst with us.

I then got WB technical to visit and i'm left a little confused by their visit. They did a software update on the boiler and reset everything to factory default settings. Plugged in the laptop and said the HEX looked fine and the pump seemed to be working ok, no error codes etc. However the problem still persisted, 70' on the LCD display within 10mins, half hour for the flow pipe to 53 and never hotter. WB technical then swapped the sensors and a pump for new. Problem still persisted.

The WB engineer then said that it was normal for the LCD display to show hotter than what the system is. And said when setting the target temp on the boiler that doesnt mean the system will get that hot.... which sounded ridiculous to me. Surely that's exactly what the target temp is for. Otherwise what is the point of it at all? I mean fine if its 2-3degrees different sure. But in our case it's as large as 20' .... he said the boiler is fine and that I should just set the target temp on the boiler to 80 rather than the 68 that it is currently.

So i gave that a try after he left, the problem still persisted with the LCD display getting hotter much quicker, the flow pipe now goes up to 62' and the boiler LCD display goes to 80... So almost the exact same differential as previous.

And, it's now displaying a new symptom where after being on CH demand for 10mins or so, it started to alternate between 20% and 80% burner output quite frequently over the space of a minute. It carried on doing this for the best part of an hour before settling at 40% eventually then stayed there stable-y... ontop of everything else would that help suggest where the failure or thing going wrong is here?

video link of new symptom -

thanks again guys, sorry for bit of an essay, it is starting to turn into a saga this now. I just want it running properly. Very disappointed in WB Technical.

Thanks for posting back, this is almost beyond belief that the boiler flow pipe is almost 20C lower than the alleged boiler target/flow temperature, just a very basic calc....the 28mm boiler outlet pipe will contain ~ 0.49L per meter, call it 0.5L/meter so when the boiler has reached 70C (or any temperature) then even a ridiculously low flowrate of say 5LPM means the temperature of the pipe should reach the same temperature (70C or whatever) in 60*0.5/5, 6 minutes measured at one meter from the boiler or in 3 minutes if the flowrate was 10LPM, once a steady state boiler temperature is reached then there should be little or no difference.
It just doesn't make any sense, did you say that it is a combi?....just thinking.

Have you changed the pump settings since WB restored the boiler default settings?,

Something is not giving the correct readings.

What's the gas rate on max?

How far away is the pipe stat sensor from the boiler and is the sensor properly bonded to the pipe with thermal paste? Have you cross checked them with say an infra red thermometer, with a bit of black tape around the pipes?

Johntheo5 said:

Thanks for posting back, this is almost beyond belief that the boiler flow pipe is almost 20C lower than the alleged boiler target/flow temperature, just a very basic calc....the 28mm boiler outlet pipe will contain ~ 0.49L per meter, call it 0.5L/meter so when the boiler has reached 70C (or any temperature) then even a ridiculously low flowrate of say 5LPM means the temperature of the pipe should reach the same temperature (70C or whatever) in 60*0.5/5, 6 minutes measured at one meter from the boiler or in 3 minutes if the flowrate was 10LPM, once a steady state boiler temperature is reached then there should be little or no difference.
It just doesn't make any sense, did you say that it is a combi?....just thinking.

Have you changed the pump settings since WB restored the boiler default settings?,

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Hey @Johntheo5 I have yeah, it's back on setting 0 (relative to the burner) but also set the min to 80% max 100% as recommended by the WB technician.

Though there definitely is something weird going on in the Hydraulic settings that's hugely inconsistent with the manual. Not sure if its a printing error or an issue with the software on the boiler, but on factory reset 2-A1 is default 0, fine, 2-A2 is default as 1 on my boiler... so inconsistent with the manual. And even weirder than that, 2-A3 and 2-A4 aren't even options for me. Unless I set 2-A2 to 0, then 2-A3 does appear as an option but only gives me 0 and 1 to choose from in that setting...... 2-A4 is never there.

Something is really messed up here. I wonder if it's related to why the heat differential issues we're seeing here?

dilalio said:

Something is not giving the correct readings.

What's the gas rate on max?

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When it's running at 100% it uses about 34kw hr

Madrab said:

How far away is the pipe stat sensor from the boiler and is the sensor properly bonded to the pipe with thermal paste? Have you cross checked them with say an infra red thermometer, with a bit of black tape around the pipes?

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It's about 15cm below where the connection point of pipe to boiler is. So really close. I've tried now with 4 different instruments, including one that WB guy brought with him) it's definitely accurate the readouts on that pipe. 53 tops or so, and each of the flow pipes on the rads is there about that too. or within a few degrees.

it's only the boiler that's miles out from everything else.

GeddyMortgage said:

Hey @Johntheo5 I have yeah, it's back on setting 0 (relative to the burner) but also set the min to 80% max 100% as recommended by the WB technician.

Though there definitely is something weird going on in the Hydraulic settings that's hugely inconsistent with the manual. Not sure if its a printing error or an issue with the software on the boiler, but on factory reset 2-A1 is default 0, fine, 2-A2 is default as 1 on my boiler... so inconsistent with the manual. And even weirder than that, 2-A3 and 2-A4 aren't even options for me. Unless I set 2-A2 to 0, then 2-A3 does appear as an option but only gives me 0 and 1 to choose from in that setting...... 2-A4 is never there.

Something is really messed up here. I wonder if it's related to why the heat differential issues we're seeing here?

View attachment 402370

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"but on factory reset 2-A1 is default 0, fine, 2-A2 is default as 1 on my boiler... so inconsistent with the manual"

Low Loss Header
2-A1 is showing 1? NO LLH (and you dont have one)

Hot Water System
"2-A2 is default as 1 on my boiler" Is your boiler showing 1?, if not, what is it showing??

How are you getting hot water now??.

Johntheo5 said:

"but on factory reset 2-A1 is default 0, fine, 2-A2 is default as 1 on my boiler... so inconsistent with the manual"

Low Loss Header
2-A1 is showing 1? NO LLH (and you dont have one)

Hot Water System
"2-A2 is default as 1 on my boiler" Is your boiler showing 1?, if not, what is it showing??

How are you getting hot water now??.

Click to expand...

Hot water comes from somewhere else. This is a CH only system boiler.

2a1 is showing as 0 on mine as default. And consistent with the manual.

It’s showing 1 on 2A2 since the factory reset. But the manual says that should be 0 by default I’m wondering why there’s an inconsistency there. That said, In my case because we don’t have any demand for hot water. I presume I should set it to 0? I’m just confused as to why it’s defaulting to 1.

When I did try setting 2a2 to 0… it then gives me the option to set things in 2a3. No idea why.

2-A2 if defaulting to 1 shows that there is a 3way valve installed, if so, then I'm not sure but it could mean that the boiler can be configured to give PDHW (Priority Domestic Hot Water) and may have other (2?) boiler connections that can go to a cylinder coil flow&return.
Does the flow pipe still read way lower than the displayed boiler target&flow temperature whether you have it (2-A2) set to either 0 or 1?.

Johntheo5 said:

2-A2 if defaulting to 1 shows that there is a 3way valve installed, if so, then I'm not sure but it could mean that the boiler can be configured to give PDHW (Priority Domestic Hot Water) and may have other (2?) boiler connections that can go to a cylinder coil flow&return.
Does the flow pipe still read way lower than the displayed boiler target&flow temperature whether you have it (2-A2) set to either 0 or 1?.

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I’m going to try setting it to 0 tonight and see what happens.

I’ll take a photo of the under side of the boiler. In our case it’s definitely just 4 pipes (flow, gas, blow off?, and return). Though I can see slots for where more pipes could be added, it’s my understanding that the boiler shares slot of DNA with its combi sister.

How could I confirm if it has a 3 way diverted or not?

Photo of underside of boiler below