Yes this is the metal flange the sump pushes onto. The boiler is about 6 years old. I bought the property a year ago. I took out a homecare plan with british gas as the boiler had a bad history. It packed up the day before the engineer came over for an intial visit to service the boiler before the plan started. He belived from the state of it that no maintenance had been carried out, hence all the corrosion.