Worcester Bosch Greenstar 8000 System Boiler Issues

[EinTopaz]

1 hour ago, EinTopaz said:

Hey, hope you all had a lovely Christmas. Ours was lovely despite the boiler still playing up after all this.  

I ran it yesterday with exactly the same settings as previous, got to target of 60'c in 25mins like last time. I had to nip out to go get the family, came back 10mins later and the boiler was down at 51c again, and a really low output % on the burner. I never got to witness it happen but in the past this is because it's exceeded the target temp by > the set threshold and turned the burner off for 2mins.  It's annoying I never was logging the data for that run but i'll do another today and see if I can replicate it. If it did do that then the issue from my last post where it was taking a while to modulate down despite going 5c over target...appears to be getting worse, as in its going higher and higher over target each time, i'll confirm that today.

EDIT: Infact looking at the settings, I did change one thing, I raised what I thought was the threshold before it would trip out, from 6c to 10c. I think that's what this setting is for anyway in the image below. Maybe I misunderstood it. 

 

Image didn't attach, its this one, i thought that meant "target can be exceeded by this many degrees before it turns the burner off" but on reading and testing again I dont think it means that. I think that threshold is hard coded to the boiler

 

and what this option means is "after the burner has turned off from overshooting, how far do you want the temp to drop before the burner re-ignites?"  I'm fairly confident it means that now. 

 

 

 

 

Edited 23 hours ago by EinTopaz

[John Carroll]

24 minutes ago, EinTopaz said:

HIVE. 
 

Just using the boost function it. As far as I know it doesn’t do any modulating itself. Just on/off

 

 

im running the heating again now with a lower pump speed. It hasn’t tripped off this time which is annoying. Target still 60. It over shot to 65.5 and is still at 65.5 now 20 mins after reaching target

 

With lower pump speed the flow / return dt was closer to 25 than 20 for the most part. It’s now at 18. Or so. 

No way should the boiler behave like this, under steady running conditions, like above, the only reason that the flowtemperature exceeds the targettemp up to the burner trip point and recycle is when/if the minimum boiler output is > than the rad(s) demand, can you repost that thumbimage above or just take a screenshot as I can't open it.

 

OK see it now, above, I don't think that has anything to do with the burner tripping when the flowtemp exceeds the targettemp, its to do with the anticycle time, on at least some of these WBs you have two parameters for setting the anticycle time..... a time (minutes) and a (negative temperature hysteresis) where the "longest" one wins, it goes something like this, if the time is set to say 5 minutes and the hysteresis set to (-) 6C, if, after burner cut off, the 5 minutes  time has elapsed but the flowtemp hasn't reac hed targettemp -6C then the burner will not refire until the flowtemp does reach targettemp -6C, if the flowtemp had reached targettemp - 6C, then the burner will not refire until the 5 minute time has elapsed, or something like that.

 

Most burners will trip at targettemp+5C.

Edited 23 hours ago by John Carroll

[JohnMo]

1 hour ago, EinTopaz said:

threshold before it would trip out, from 6c to 10c

So that is just the restart hysterisis.

 

Doesn't the lower pump speed, just drive a lower output of the radiators, and then drive shorter boiler cycles, as there is less to take the boiler heat away?

 

 

[EinTopaz]

2 hours ago, JohnMo said:

So that is just the restart hysterisis.

 

Doesn't the lower pump speed, just drive a lower output of the radiators, and then drive shorter boiler cycles, as there is less to take the boiler heat away?

 

 

id have thought so. But looking at the data I logged side by side with the previous test. It reached target temp around about the same time. All rads felt hot. The only difference was the dt was mostly around 25 rather than 20 in the test previous. Whether that’s better or worse. I couldn’t say. 

 

edit: previous test was pump setting 6 at 400mbar, this test was pump setting 4 at 300mbar  

 

Edited 20 hours ago by EinTopaz

[EinTopaz]

2 hours ago, John Carroll said:

No way should the boiler behave like this, under steady running conditions, like above, the only reason that the flowtemperature exceeds the targettemp up to the burner trip point and recycle is when/if the minimum boiler output is > than the rad(s) demand, can you repost that thumbimage above or just take a screenshot as I can't open it.

 

OK see it now, above, I don't think that has anything to do with the burner tripping when the flowtemp exceeds the targettemp, its to do with the anticycle time, on at least some of these WBs you have two parameters for setting the anticycle time..... a time (minutes) and a (negative temperature hysteresis) where the "longest" one wins, it goes something like this, if the time is set to say 5 minutes and the hysteresis set to (-) 6C, if, after burner cut off, the 5 minutes  time has elapsed but the flowtemp hasn't reac hed targettemp -6C then the burner will not refire until the flowtemp does reach targettemp -6C, if the flowtemp had reached targettemp - 6C, then the burner will not refire until the 5 minute time has elapsed, or something like that.

 

Most burners will trip at targettemp+5C.

Yep makes sense, I couldn’t get it to trip this time. I have a feeling the trip is +6c on this boiler. It went up to 65.6c in today’s test. When it does trip again though I’ll be able to confirm the 3-b3 setting above. I’ve set it to -2now. So I’m expecting the behavior to be… if/when it next trips above target, it’ll drop to 58 then fire up again. Where’s at -10 I suspect it waited all the way down to 50 before firing up again. That’d explain the gap where I wasn’t monitoring yesterday. 
 

But yeah the larger concern is… why is it exceeding target by nearly 10% at all?! 
 

Perhaps I should range rate it down too to maybe like 85% max and see if that affects heat up time / and / or helps this over shooting issue. 

Edited 20 hours ago by EinTopaz

[marshian]

4 minutes ago, EinTopaz said:

Perhaps I should range rate it down too to maybe like 85% max and see if that affects heat up time / and / or helps this over shooting issue. 

 

I wouldn't expect range rating it down to impact the overshoot unless it was RR down to less than the circuit can accept in which case the temp wouldn't over shoot for a long time - equally the house would be also slower to warm up. 

 

Plus your "85%" might be fine for now but when it's -2 outside and you want to throw a bit of heat at the house it could potentially result in a lot slower warm up.

 

IMO the only time you can be justified in RR a boiler is where the boiler capacity is massively in excess of the house heat loss and even then with a scheduled heating (or as and when you think it needs it in your case) you are going to need plenty in reserve to bring the house up to target temp so probably not much point RR'ing the boiler

[John Carroll]

11 minutes ago, EinTopaz said:

Yep makes sense, I couldn’t get it to trip this time. I have a feeling the trip is +6c on this boiler. It went up to 65.6c in today’s test. When it does trip again though I’ll be able to confirm the 3-b3 setting above. I’ve set it to -2now. So I’m expecting the behavior to be… if/when it next trips above target, it’ll drop to 58 then fire up again. Where’s at -10 I suspect it waited all the way down to 50 before firing up again. That’d explain the gap where I wasn’t monitoring yesterday. 
 

But yeah the larger concern is… why is it exceeding target by nearly 10% at all?! 
 

Perhaps I should range rate it down too to maybe like 85% max and see if that affects heat up time / and / or helps this over shooting issue. 

Can you post a E link to a exact copy of your paper MIs?.

[marshian]

20 minutes ago, EinTopaz said:

id have thought so. But looking at the data I logged side by side with the previous test. It reached target temp around about the same time. All rads felt hot. The only difference was the dt was mostly around 25 rather than 20 in the test previous. Whether that’s better or worse. I couldn’t say. 

 

I think I've said this before - be careful if you end up with a DT greater than 20 Deg at the boiler most modern condensing boilers really don't like this much and will do all sorts of things to try and protect themselves.

 

If you are getting a wide DT with a slower pump speed then you could probably lower the flow temp to tighten the DT (at the expense of slightly cooler rads but I wouldn't think the difference in rad temp between 60 and say 55 would be detectable by touch)

[EinTopaz]

23 minutes ago, John Carroll said:

Can you post a E link to a exact copy of your paper MIs?.

https://www.worcester-bosch.co.uk/support/literature/download/release/6720883858/45568

 

Goes into the settings from around Page 51. 

[SimonD]

29 minutes ago, EinTopaz said:

But yeah the larger concern is… why is it exceeding target by nearly 10% at all?! 

 

The boiler is essentially dumb and slow to respond. It measures just flow temperature so by the time the return temperature has reached the point at which flow temperature increases the heat is already in the system, so there's always going to be some intertia. It's not sensible from a design perspective to make the system respond too rapidly as that affects operating efficiencies and can cause various unwanted attempted control oscillations within the system.

 

The real issue here is that the focus at the moment is only on the boiler and not your controls together with your boiler. At present, even though they might call it a smart thermostat, it's actually pretty dumb because the Hive only provides relay control of your heating. To get this boiler modulating properly in relation to room temperature or outside temperature you need some decent controls that actually modulate the boiler - so either weather compensation, or if you want load compensation, something like the Worcester Easy Control which uses EMC Bus to communicate with the boiler. You can use Opentherm to do modulation, but only with a third party translation kit that you need to get from Europe.

 

Get yourself some proper controls and the boiler will behave much better and can be refined from there.

 

[marshian]

4 minutes ago, SimonD said:

The real issue here is that the focus at the moment is only on the boiler and not your controls together with your boiler. At present, even though they might call it a smart thermostat, it's actually pretty dumb because the Hive only provides relay control of your heating. To get this boiler modulating properly in relation to room temperature or outside temperature you need some decent controls that actually modulate the boiler - so either weather compensation, or if you want load compensation, something like the Worcester Easy Control which uses EMC Bus to communicate with the boiler. You can use Opentherm to do modulation, but only with a third party translation kit that you need to get from Europe.

 

Get yourself some proper controls and the boiler will behave much better and can be refined from there.

 

The issue there is the dumb controls are all @EinTopaz requires for the way he uses the heating system

[John Carroll]

3 hours ago, EinTopaz said:

 

 Target still 60. It over shot to 65.5 and is still at 65.5 now 20 mins after reaching target

 

 

It doesn't matter what kind of fancy controls or otherwise it may have, maintaining a alleged targettemp+5.5C for 20 minutes smacks surely of some boiler control problem, especially since the boiler minimum output is way below the steady state rad demand.

[EinTopaz]

What would be reasonable next steps then guys? get WB out again and show them that it's going way beyond target and fingers crossed I can get it to trip out on the day?  As it stands they have swapped out the pump, sensors, Hex, and they did the board last Monday too. 

Not sure what else to do other than keep running it with slower pump speeds and seeing if that fixes anything.

I have noticed a whole bunch of weird inconsistencies in the manual, particularly in the L2 hydraulic settings, the settings on my boiler are not consistent with the ones in the manual. But WB told me because i simply have flow/return/Gas and no cylinder or diverter etc, then it doesnt really matter about L2.... again not sure if im being palmed off there again or they're right on that one. 

 

[marshian]

3 minutes ago, EinTopaz said:

What would be reasonable next steps then guys? get WB out again and show them that it's going way beyond target and fingers crossed I can get it to trip out on the day?  As it stands they have swapped out the pump, sensors, Hex, and they did the board last Monday too. 

Not sure what else to do other than keep running it with slower pump speeds and seeing if that fixes anything.

I have noticed a whole bunch of weird inconsistencies in the manual, particularly in the L2 hydraulic settings, the settings on my boiler are not consistent with the ones in the manual. But WB told me because i simply have flow/return/Gas and no cylinder or diverter etc, then it doesnt really matter about L2.... again not sure if im being palmed off there again or they're right on that one. 

 

 

What are your L2 settings? I would have thought it was pretty important to have the correct parameters??

[John Carroll]

I would suggest, under steady state running, get the flow/return dT to less than 20C, say 18C, assuming the target & flow temps are equal, take readings, then slowly decrease the pump speed, (you can use your max clamping method to achieve this), the dT will keep rising, see if the flowtemp starts to exceed the target temp as the dT increases, keep reducing the pump speed until the flowtemp exceeds the target temp by 5.5C (trip point?), note all readings.

Before doing,  (if) I would increase the anti cycle time to 5/6 minutes again.