Did they send an entire replacement kit including fan? Are you using the new fan or the old fan? Are you using Corsair Link with the new H80i or just letting everything run at full speed?
And Waco makes a good observation about your previous temperatures seeming low. What were the ambient temperatures when you made your observations when using the H80? What are the ambient temperatures when you're making your observations on the H80i?
I think a reasonable assumption is that with your particular cpu, at that clock speed, at that voltage, using the H80i (if it's functioning correctly and installed the right way) is that your loaded CPU temperature will be somewhere between 35 and 42C warmer than the ambient air temperature.
Yes I have new complete kit with new fans. I've played around with Corsair Link settings and it did not do much difference from settings fan speeds to balanced to performance / full speed etc.
Sorry I forgot to mention that idling 20-25 with my h80i was normally during Winter - ambient temperature usually goes down well below 20. However in hotter days, my old h80i would give me idle temps of around 27-33 (give or take)
In the case of the H80i, ambient temperature was around 24 degrees with the AC on.
What really matters is the load temperatures (using prime95) though. With the same ambient temperature and at the same clock speed/voltage, the H80 would give me temperatures of around 60 while the new cooler almost reached the 80s. The stock cooler does not perform much far away from the latter I may add...
It might simply be that the new fans are set for a much lower speed. What profile are you using with it in Corsair Link?
As I said above, I've tried all type of settings but did not make a large difference.
I have the h100i cooling my 2500k clocked at 4.3GHz, and I get around 29-32C at idle with a room temp of around 22C. During load it gets up to around 65C degrees, maybe 68C. I have the two fans that followed with it and a quiet edition SP120 fan hooked up to it, all runing around 1200rpm during load. So I'd say your original temps seem quite low, unless your room is below 20C ambient. But the new idle temps seem quite high.
I don't know about the h80i, but my h100i needed some washers inbetween the waterblock and the mounting bracket due to a small gap, and it's a problem with all h10i afaik. That might be the issue?
Also, it is also good to mention that I am currently using an Asrock z77 Extreme4 board instead of my p67 fatality pro (RMAed). So the new H80i has only been tested out on the z77. Although the cpu block seems tightly fit to the board, can a loose backplate be causing a problem? I've found a thread were a guy mentioned that the Extreme4 is kinda thin and would need extra washers to secure the backplate to the board. In fact, I'll try it out this weekend and let you all know.