Where is the reset button ?

RTFM

http://www.potterton.co.uk/downloads/Potterton_Performa_24_Eco_HE_Install.pdf

Page 7

http://www.potterton.co.uk/downloads/Potterton_Performa_24_Eco_HE_User_Guide.pdf

Page 3

You may need pages 4 and 5 as well, depending on why you are asking the question.

We'll leave aside, as a reason for you asking here, the notion that you couldn't be arsed to do a Google search for yourself. FYI It took me about 2 minutes to find the manuals AND check for references to a reset control.

XXX
February 2016