The pressure switch or water level sensor is the small electric or electronic control component that determines first of all, if there is water in your John Lewis dishwasher and then, when there is enough water to begin the program and allow the heating element to be energised. They are generally a reliable spare part and not prone to failure however, they can and do fail.
Pressure sensors are range if not model specific and it is important to order the correct switch for your particular John Lewis model, substitution or guessing is not normally an option so please do take care to ensure that you order the correct one for your John Lewis dishwasher model specifically.
For technical help and support for your John Lewis dishwasher please use our dishwasher forum where you can get expert help from dishwasher repairer technicians. There is also a lot more help and advice about dishwasher faults in the dishwasher self help area of the website.