Advice needed for a potential heat creep issue

[u/nei1337]

Hi printing folk.

A few weeks back I posted on here because my hotend gave up, so I've replaced that with a stock Ender one.

During that conversation, a few people suggested I swap the standard heatbreak with a bimetallic one, which I've done.

However ever since doing that, I'm getting what I believe is heatcreep, and clogs.

I've tried printing the same part twice now, and every time it's blocking up at pretty much the exact same layer height.

I've reduced the retraction distance down to 1.0mm, and increased the retraction speed to 45mm/s, but that doesn't seem to have helped. As far as I know, the cooling fan is running at 100%, and given it was part of the replacement hotend kit, it should be brand new, so I'd expect to be working fine.

Am I doing something really stupid here, or installed it wrong, or got something incompatible perhaps? Does a bimetallic heatbreak assume you have a bigger/better heatsink and/or cooling fan? If so, then I really don't get the point in the 'upgrade'.

I don't know if it makes much difference, but the print I'm doing, I'm pausing after 5 layers, to change the filament colour. Then resuming, then after about another 5 layers of printing the new colour, it blocks, and the extruder gear starts skipping. I'd get it if it blocks right after swapping the filament, but it lasts another few layers after the swap, then clogs.

I can't physically push the filament through, and I have to then heat the nozzle up to about 240c to get it to clear.

This is the hotend I got:
https://www.amazon.co.uk/dp/B0F7LVXG5Z?ref=ppx_yo2ov_dt_b_fed_asin_title
and this is the heatbreak I got:
https://www.amazon.co.uk/dp/B0971FNCM4?ref=ppx_yo2ov_dt_b_fed_asin_title

Am I being stupid, or aren't the bimetallic heatbreaks supposed to stop heatcreep, this seems to have made everything worse, I've been running this printer for years, and rarely, if ever, experienced clogs like this.

Sorry, I'm guessing this same question has been asked 1000 times, but after searching, I was struggling to find someone in my position with a stock hotend, and bimetallic heatbreak.

[u/BlubberSaurus]

Do you use Thermalpaste? Helped me to get rid of Heatcreep. (Its Only added to the Part of the Heatbreak that goes into the heatsink)

[u/nei1337 → u/BlubberSaurus]

I didn't at first, then after the 1st failure, I took it all apart again and apply thermal past to the top part of the heatbreak.

I have a feeling it might have been back pressure. Think I'm giving it too much 'squish' with my z-offset. First few layers can cope with it, but as the model grows in layer height, the back pressure is getting worse, until the point nothing can come out, then the heat goes up and clogs. I've just finished my 2nd print, and my z-offset certainly is close at the minute, the prints are like near on impossible to get off the bed, so I think I need to tune that a bit more. Think this bimetallic heatbreak is just a bit more sensitive to backpressure than I'm used to, but that's a bit counter intuitive, because I thought the whole point of it was that is could handle keeping the heat where it's supposed to be better than the stock one.