Worcester Bosch Greenstar 8000 System Boiler Issues

[John Carroll]

46 minutes ago, EinTopaz said:

I’ll give that a try. But I know already from testing that the 90% range rated test I tried yesterday took 5 mins longer

to get To target. Still overshot but only by 3.6c this time. But then weirdly never did make its way down to 60. It settled at 62.5 with a modulated output of 54%
 

I assume the higher modulated % was because it was a colder day and the pipes are in the subfloor with the ventilated air bricks etc. so assume it was just working a little harder to keep them at temp. Or above! 
 

EDT ^ this was all on pump setting 5, which was essentially locking it at 87% pump speed 

If you are happy enough with that overshoot then why not leave well enough alone, you probably may not have even noticed it if you hadn't had the other big problem.

 

But no way  IMO should the there be a offset of 2.5C between the target and flow temperature once steady state conditions are achieved, these controllers are/should be PID, where the "I", (integral) will achieve zero deviation between the target and flow temperatures especially under these benign conditions, you might see + or - 0.1/0.2C deviation now and then, the colder day/pipes etc has nothing to do with the control, the controller is just looking at the process variable which is the flow temperature in this case.

 

Edited 12 hours ago by John Carroll

[EinTopaz]

9 hours ago, John Carroll said:

If you are happy enough with that overshoot then why not leave well enough alone, you probably may not have even noticed it if you hadn't had the other big problem.

 

But no way  IMO should the there be a offset of 2.5C between the target and flow temperature once steady state conditions are achieved, these controllers are/should be PID, where the "I", (integral) will achieve zero deviation between the target and flow temperatures especially under these benign conditions, you might see + or - 0.1/0.2C deviation now and then, the colder day/pipes etc has nothing to do with the control, the controller is just looking at the process variable which is the flow temperature in this case.

It’s a fair point, it’s not the most egregious thing now everything is getting warm enough. To be honest the overshooting in and of itself isn’t bugging me, I’m fine with everything getting a littler hotter then I’ve set… though what is bugging me is more the fact it’s staying at 100% of its rated output long after it’s reached target. It’s working way harder than I’ve asked it to and the bottom line is that’s costing me unnecessarily everytime I run it.

 

For every hour it’s running at 35kw it costs around £2. So that will add up a lot through the year if it’s not modulating down when it could/should.

 

 

as a slight aside. Do you know the best insulation method for pipework that runs in a ventilated, unheated subfloor. The pipes are already lagged but wondering what else I can do to keep them as optimally warm as possible.