were is the pressure sensor located on a Vaillant Eco 824?

I have a Vaillant eci 824 boiler, displaying Fault .75. Accordnig to what i have read online it is the pressure sensor that needs to be replaced as this seems to be a common fault with this unit. Everyone seems to think that it is a simple task to exchange this part, however i have two problems. the first is that the boiler is in a cabinet in the kitchen as im not sure of the location of this sensor i dont fancy dismantling have the kitchen to get to the underside of the boiler. can anyone please tell me were this sensor is located? can anyone also confirm the correct part number as one of the parts supplier that did want to help, couldnt as they need a part number. anyones help would be greatly appriciated. have a great Xmas