EinTopaz

Yep, from monitoring i think this is just standard behaviour from modern boilers. Though as part of the test yesterday I did try setting the burner min output% to 45% (default is 14%). It did shave a few minutes off reaching 60c, but i think it also caused further problems with the boiler not being able to properly modulate down once it had hit/exceeded target temp. I need to confirm that today with another test, may've been a coincedence. Yes exactly, thats the behaviour i'd expect to see. If the system doesnt demand as much power as the boiler can give, ie if some of the TRV temps get hit and the radiators turn off, i'd expect the boiler to modulate down, not just carry on and overshoot the temp at 100% output. That just seems ignorant and primitive to me, I agree with you that this doesn't seem like its part of normal programming, this boiler doesnt have a return temp that i can monitor on the LCD, but it must have a sensor inside thats being checked to determine the modulation beyond the flow temp? From memory they have changed a couple sensors already but that was to try and fix the massive difference we had back when the HEX was screwed. Maybe theres more sensors on there that need to swap thats causing this? When i run it now with all the radiators fully on, ive got the target set at 68c, it will overshoot this by 4c, very occasionally it will overshoot it by more and turn the burner off. But that's more rare when all the radiators TRVS are on. When it doesn't trip off, as mentioned previously it will take as long as 30-45 mins to come back down to target. Modulating verrrry slowly as it goes. My own sensor is now 1C difference to the boiler LCD display. That's a good question, do you mean if i change it once the target temp has been reached and everything is stable? i'll give that a try. From memory i dont think it reacts at all to this. Before hex replacement i cant recall, I feel it was still overshooting back then.... it must've been as it was going quite high on the LCD display, why do you ask? do you suspect theres been a problem since they swapped the hex and thats causing the overshooting?

I'll spend thousands for a thing to function correctly and me not have to fanny around with it, yes. In simple terms it takes too long to heat up my system and its not running cheaply enough to outweigh the time i have to wait for it to heat up. Id rather go for a commercial boiler at this point. it was on one system at one point but its been extended many times now. I cant be bothered linking it all back together now, rather have 2 boilers. I just need my downstairs one to be less shit. Incase I hadn't mentioned 🙂

That's fair re: boilers not being too reactive, but it does seem awful slow to react this one. Like it carries on way past the target at nearly full strength output. I'll do a longer test next time to show you but it really does take a while for it to come back down to target. That doesn't seem efficient to me and means it does sometimes turn the burner off if it exceeds the target too much. None of that seems like its doing what it should to me. Maybe 10minutes to react and load its self down would be fine, but in my case its way longer. My expectations and frustrations are two fold with this boiler, they were three until the hex got fixed, now just the two. They are - I want the rads to get hot sooner, and, I want the thing to run efficiently and modulate down correctly. (the overshooting stuff above bothers me regarding efficiency). If it fixes both the frustrations; I am prepared to put the boiler in the bin if I need to and go for a larger Vaillant conventional type. This one is 35kw and doing 28kw-ish of rads at T50 Perfomance wise, i want it run more like the other boiler I have at this property. I'll put the data log of that one below. Its 41kw CDI conventional (with grundfos 25-55 pump) and powers around 22kw of rads. i've no issues with that boiler. It warms up fast, Runs exactly as I want it to. im sure it is overpowered for that system but again, no issues with overshooting or anything like that. Just works (tm). I wish the greenstar 8000 life in question here ran more like that.

Hey all sorry was away for a bit on holiday... lovely not having to stress about heating when you're in a warm country eh. I ran some more tests and logged the data. I may have mentioned already but I have a mix of type 22 and triple column rads in this system too. Those triple column rads always take a lot longer to warm up because of the amount of water content in them, its maybe 70L just in those as they're huge. So i wanted to do an A/B test with all rads on Vs all rads on bar the triple column ones. To see if it would affect the ramp up time by much. My thinking was, if the heat up time is very similar then the issue is likely that the pipes in the subfloor are losing lots of heat (as they're maybe 50-60meters of piping down there in total). Also taking your advice from the forum I ran both of the tests in pump setting 0 (proportional to burner mode), in which the range min was set to 60% and the max set to 100% Test A was all rads on, Test B was all rads on Bar the triple column ones. Note: i've set the target to 68c now rather than 60 just to see if it helped speed the ramp up too. On test B it did heat up quicker, but also tripped the burner out at 27minute mark....I imagine because without the triple column rads TRV's on, it was just too much heat for the system. I've got a few other things i want to try in my next set of runs.... but before I speak to them, what do you think of the above? On Test A i'm still a little baffled that the boiler is reacting so slowly to modulating down.

Will a LLH stop the boiler overshooting and tripping out atleast? As it is still doing that and it does concern me despite what Bosch say about it being by design. Also, in the test I did last night, I turned off the 4 triple column rads at the TRV to see if that'd drastically speed up the flow temp ramp. As they do have a huge capacity of water, something like 80L for the four of them. So figured if those weren't needing to be heated i'd see a much quicker journey to target temp, but I did not. Wondering if the system (pipework) in and of itself is just too long and cold for this boiler and its internal pump.

Hey, it's just personal preference. I've replied to a separate comment showing the difference between my boiler upstairs and this one. Thats the behaviour and characteristics i want. Fast heat up. And prepared to amend what I need to do to achieve that. its important to me and this project.

I will, but im already aware it doesn't start at 100% burner output when turned on from cold. it starts at maybe 22%, is around 75% by the 5minute mark and 100% by 8-10mins, i'd need to double check but thats roughly correct. When I draw a comparison to my upstairs CDI boiler. This is where I get frustrated...I want the 8000 life boiler downstairs to behave more like that. I'm happy to forfeit some economy in trade for a quicker heat up. I logged the the temps and times on the upstairs boiler before. it does ramp much quicker. Let me put them below. I wish my boiler downstairs heated up as quick as it did. WB CDI boiler (upstairs) 0 minutes Flow 15 Return 15 5 minutes Flow 46.5 Return 19.2 10 minutes Flow 54.8 Return 29.2 15 minutes Flow 55.2 Return 39.2 20 minutes Flow 55.2 Return 46.0 After that the temps don't change on the upstairs boiler. All rads are plenty hot enough by the 10min mark. Obviously I can't see the output % on that boiler's LCD with it being more primitive. But I presume its 100% from the start, or atleast has a much more aggressive ramp. Which I like. With regards to the downstairs boiler ....Next time i do the logging for that one, i'll paste that here too. I will have mentioned before but there are 4 x triple column vertical rads on that downstairs system with alot of water in them. And the pipework for the downstairs boiler is all in a ventilated sub-floor, theyre lagged but only with the cheap foam stuff. So I reckon all of these things are contributing to the longer warm up time. That said if I turn off half the rads downstairs on the greenstar life system, I should expect to see the target of 60c hit much sooner right? if not then would it then be fair to say i need an LLH?

Now that the HEX is sorted and its dispaying the temperatures correct. I want the system to heat up alot faster. The LLH was an option I was considering but doesnt have to be that solution. I have a CDI upstairs, conventional, it does the radiators in this property for the top 2 floors. 22KW rads total @t50 or so. The rads on that system are hot within 10 mins. Which is what I want my downstairs boiler to be like, the downstairs boiler is the greenstar 8000 that we're discussing here. That one takes 30mins for the flow to reach 60 target. The upstairs one takes 10-12mins to get to 60 target. I mean, there isn't a huge amount of difference in the power of these 2 boilers. So im trying to do what I can to get it so the downstairs boiler can heat up faster. Hence second pump, hence LLH. Do you have any other suggestions I can look at? besides swapping the boiler out entirely.

Thanks John, I’m not the most technical so will need that simplified down a touch for me. How do I know what LPM will be enough for my system if I want it to heat up quick? If it’s 27kw of rads. And a mix of 28mm / 22mm / 15mm pipe (mostly 22mm)

Thanks, so looks like I’d be best going with an LLH and add an adjustable external pump too then maybe something like a 25/65? And basically monitor the temps on both sides and adjust accordingly. I’ve read on the LLH if it’s unbalanced it can either short cycle the boiler or pull colder water through to the system. That seems like the only way to proceed or chuck out the boiler and go for a conventional type instead.

OK they've been back out. And ultimately said the overshooting is within tolerance and part of the design. They monitored it remotely with their software guy and said it basically is operating as expected. And claimed that the prolonged modulating down and overshooting is because of system balance. Which did sound wrong. But feels like ive exhausted all i can with that team now if theyre basically coming back and saying there are no problems. I could go to trading standards but not sure how id even try and prove their wrong honestly now. Regarding the hex pressure loss, he said they dont have that in the documentation for the system boilers, but its the same as the conventional boilers and sent me an image of what they are, which i've attached. Lastly when asked about running a second pump on there, he said absolutely not unless theres mechanical separation, as in an LLH. He didn't say why, but was very clear on that being a no-no.

Oh interesting, so in simple terms its limiting to 400mbar because the boiler wont let it go higher? Knowing all this would the plan for adding the Wilo Yonos Pico as an extra external pump still be valid? as I was still planning to do that after the WB boiler guy takes another look. I dont want to over complicate the setup before they come back as in my experience that makes it easy for them to point to other things as a cause of the problem. Currently there's nothing external other than the mag filter and extra Expansion vessel.

They cancelled on me and are coming on the 6th Feb now to look at why its still overshooting etc.

Picking up on a slightly earlier topic in this thread that I want to revisit. As well as the boiler in question here that's having the problems... im using a separate boiler upstairs for CH on the top floors, I may've mentioned already, but it is a 40kw CDI conventional CH only. (it's that large because it used to do the entire property before we extended etc). That powers 10 x type 22 rads/ circa 18kw, and is set to setting 4 (8max) on the potentiometer on the front, this means it gets to 65c. All the rads on this circuit get warm within 5mins, and hot within 10minutes. It's 22mm piping for the first 3meters, then drops to 15mm, then down to 10mm down the wall cavities to each of the rads for the last 2meters or so, so id assume way more resistance in this system than the boiler downstairs (the one i'm having all the problems with in this thread). Also worth mentioning The pump on this is external and a grundfos 25-55. On the boiler downstairs, the one i'm constantly having problems with. I have wondered now that the HEX is fixed and the temps are atleast displaying correctly, if I wanted to speed up the heating time to get it closer to the boiler upstairs, what can I do to improve it? I've looked inside this system boiler now and can see it has a 15-70 pump in there. Which does make me wonder, does that essentially make it a stronger pump with more head than the one I have upstairs? and if its 15-70, why is setting 6 (400mbar) show as pump output 100% on the boiler LCD display? Does that essentially mean its got way more head than it's able to use? i.e it's capable of 700mbar, but can only run 400mbar max? I find the manual quite confusing here and it'd be great to understand this so I can work out the viability of adding a second external pump to this setup, or running an LLH and an external pump too. The goal would be hopefully significantly shorter heat up times. Images attached of the pump and the manual again, for ref.

I have, they're coming back out on the 16th Jan. I've got a 100% repro case waiting for them. And have confirmed; no matter what I set the target to, it's exceeding it by either 5c and cutting off, or very nearly exceeding by 5c, then settling at around 2-3c above target. And can also show it continually climbing at 100% output, 10s of minutes after target is reached. So in summary, not settling at target, overly slow to modulate post achieving target, far exceeding target and tripping.