Had this exact same problem a couple months ago, needed new fan silencer/intake, flue collector, burner door + burner, front case. Could not tell 100% but the actual HE looked warped along the surface, customer asked for a quote and it was around the same price as a boiler just for parts, took a while to convince him to replace it still but he came around, never serviced since a 'gas safe uncle' installed it...