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HP Recommended
HP Z420 Workstation
Microsoft Windows 10 (64-bit)

Hello community,

i have a Z420 Workstation from 2013 with liquid cooling system, my problem: The machine has sometimes a weird noise, like clicking harddisk or a relay (it isn't from hdd) or rattling, only short times. I'm not absolutely sure, but i guess it is from the water-cooler. Perhaps to much air inside or the pump is damaged.


I removed the cooler and while shaking i can hear few air inside, is it normal? I examined it visually and found absolute no signs of leakage.

My questions:

  • Can i test the cooling-unit w/ a normal pc-mainboard? Not mounted, only electrical connected to make sure, it is the cooler or not. But the plug has a 5-pin-layout instead of 4-pin, what is the pinout?
  • If the noise comes from air inside: Possible to open and refill the circuit? It seems it is an OEM-product made by Asetek. Which liquid is suitable for a refill?
  • Is it possible to mount a normal, air-cooled heatsink on the cpu? Maybe only for testing.

Thanks for input,

best regards!

HP Recommended



For the HP Z420, the liquid cooling system is only mandatory with the Intel Xeon E5-2687W (and also the v2 model)  with its TDP of 150 watt. The most other Xeon have a TDP of 115/130 watt max. And with 115/130 watt of TDP you can use the "classic" HP cooling part number 647287-001. It's very easy to find it on the Internet sales sites.




I myself had the noise problem with the water cooling system, solved by fitting the conventional system.


[EDIT] :

- Intel Xeon E5-xxxxx (Sandy Bridge EP) => https://ark.intel.com/content/www/us/en/ark/products/codename/64276/products-formerly-sandy-brcodena...

- Intel Xeon E5-xxxxx v2 (Ivy Bridge EP) => https://ark.intel.com/content/www/us/en/ark/products/codename/68926/products-formerly-ivy-brcodename...


HP Recommended

Thanks. No matter, that the second fan for cooling vrms is missing?


Now i'm sure it is the cooler: The noise stops when pulling the plug for it. I will test it outside and try to repair the cooler.

HP Recommended

If you don't have the Intel Xeon E5-2687W (and also the v2 model)  with its TDP of 150 watt then mount the classic HP P/N 647287-001, it cools very well and above all it's silent. It has heat pipes that cool well, so no need for a second fan on this model.


[EDIT] : Z420 processor socket = Socket 2011 / LGA2011

Cooling processor = 5 pin plug


By default vrms have a single fan towards the back.


You can also mount the optional front fan kit A2Z46AA 604781-003 (for more efficiency, without additional noise) 


HP A2Z46AA 604781-003HP A2Z46AA 604781-003




HP Recommended

There is an alternative higher cooling capacity HP heatsink/fan that works perfectly in a Z420 v2 (and a single-processor Z620 v2) workstation.  It has almost exactly twice the aluminum fin cooling surface area than the stock Z420 one.  It also has 4 thick instead of 3 thin active cooling tubes.  This was originally built by HP for the Z440, and has part number 749554-001 (which can be searched for also on eBay as can "Z440 heatsink").  There are actually two versions with the same part number... the earlier has two support screws at the rear through the thick base plate, and the newer one I like best has one screw front and one screw rear through the thick base plate.  I like the newer one because I believe it is a stronger design.  If you go for the latest version be very specific with the seller exactly what you want.  It is less common.  Functionally they are identical if the heat tubes have not partially pulled out of the base plate, and the sellers won't know the difference between the two.    The earlier one relies on the two rear screws for strength.  The later one gets strength both front and back from two screws.  I have personally bought one of the earlier version which was pulling the heat tubes out of the base plate.  Never have seen that on one of the later versions.  You can go see both on eBay.


The processor change from the ZX20 to the ZX40 generations did not change the attachment specifications for the heatsinks, so this Z440 one is backwards compatible to all Z420 and any Z620 single-processor builds.  I've put in a bunch of these for a project of souping up the Z420 workstations, including for overclocking.  The white fan plug end for the Z440 is 1 pin longer (6 instead of 5 holes) than what you see on the end of a Z420 heatsink/fan.  You just let that 6th hole hang out in space for the extra 1/8th inch off the 5-pin motherboard header HP uses on the Z420.


As part of the way HP lets a motherboard know that there is a "Performance" heatsink/fan attached they engineer in ground continuity to be seen by one or more extra pin(s) than the 4 necessary for PWM fan control.  The normal PWM order is for pins 1-4:  ground/ +12VDC/ rotor RPM signal in to motherboard/ PWM braking signal from motherboard out to fan rotor.  What HP does on its "Performance" heatsink/fan for the Z420 is add a ground jumper from pin 1 over to pin 5 at the white plug end.  For the Z440 they just added another short ground jumper from pin 5 to pin 6 at the white plug end.  Thus you can hang the pin 6 end of the white plug out in space in a Z420 when you are using a Z440 heatsink/fan.


I originally replaced the white 6-pin plug end with spare HP 5-pin plug ends I have a stash of.... it finally dawned on me that was totally unnecessary, and never have looked back thereafter.  This makes the heatsink/fan upgrade pure plug and play. 


I can overclock the Z420s and Z620 single-processor builds now with no need for water cooling. Below is a pic of this excellent upgrade that currently will cost you a bit under $20.00 USD including shipping.  This earlier version shows the two rear screws back in the shadows rather than the later version's front/back two support screws that I find to be a stronger build:


Z440 heatsink has twice cooling area....jpg

HP Recommended


I live in EU and this sparepart ist very rare and expensive, about 50€ up for used(!) part excl. shipment.


BTW: I opened my liquid cooler and found out, that the pump is "rattling": Although no visible dirt or mechanical wearing, I guess it is worn out or the electronic sometimes tends to loose control, so the impeller is vibrating.

Look at this YT-video, another AIO, but the pump and radiator are exactly the same: https://www.youtube.com/watch?v=xVthLRyN9Ss

Only OEM-mounting-bracket, very short hoses and the pcb for fan+pump-control is different.


Also tried to refill the radiator only. It is nearly impossible to avoid any air inside, i don't know how Asetek did the job in production.

Ever curious about what is inside your CPU Closed Loop Liquid Cooler to see how it works inside? I tear mine apart so you can see the inner workings of the CPU Liquid Cooler that has taken over the PC industry. Opening your CPU Liquid Cooler Voids its warranty. Do so only if you don't plan on ...
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Hi @PRogosch,


For example in Ebay : https://www.ebay.fr/sch/i.html?_from=R40&_trksid=p2047675.m570.l1313&_nkw=HP+647287-001&_sacat=0


You will have a hard time finding this spare at another price unfortunately, and only "refurbished".


Good luck. 


HP Recommended

Or, for a bit more also from France eBay,  HERE , with twice the cooling capacity, 30,00 Euro.


The HP part number that is easiest to find is 749554-001. 


The smaller one that is referenced in the posts above is quite a bit smaller than this one I've used now in about 20 Z420s and Z620s without any issues.  If you're going from a small one to a replacement small one that would be fine.  If you're going from a water cooler to a small one I'm concerned that you're going to be undercooled doing that.

HP Recommended

Yes and no @SDH,


The initial Z420 cooler p/n 647287-001 supplied by HP that I presented is efficient enough for a Xeon with 115/130 W of TDP.


Your model p/n 749554-001 may also be suitable, the user will choose.




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