The PC is running the same whether pump cable is plugged into the CPU fan header or the Pump fan header, but still get the two diagnostics Critical error messages "CPU Fan Failed"  & "TOP Fan Failed".

As I say the system is running okay, max CPU temp. 75c

Does the error come up everytime you boot, or only when you run f12 diagnostics?

Also, there's nothing you can do about f12 results.  It is programmed to check for responses to pwm from the oem dell fans, and basically only the oem fans clear this.  The startup test and monthly checks are the impprtant ones that notify you of a real fan problem.  Since you got past those I wouldn't worry about the f12 manual tests.

When booting the PC it's fine no problems, only get an error in the F12 diagnostics. From the attached photo all appears to be working ok. I guess the CPU fan speed is the pump?

I installed the h60 with a pair of ML120 Pro fans.

Swapped the front fan for a ML120

On my system now when I'm playing FPS games it sits at 38°c

And when playing cpu heavy games it goes up to 50°c

Room temp is 24°c.

Dell should of installed better fans and radiators on all spec levels. 

Machine is quiet and cool now as it was intended to be.

Do the upgrade and enjoy peeps 

The PC is working great and making very little noise. Thanks everyone for your help much appreciated