Just call them every time! No fun on a Friday night with a head full of shampoo and icy water, I know, but that's what you have to do. If they have given you suggestions or cleaned it out and it still persists, start asking about a new one. The boiler brothers are very good and know how these boilers are. Still, it has to be a complete lost cause for them to finally be able to get permission to replace your boiler. It was in our case, anyway. The tech still kids me about that old boiler every time they come to do maintenance :)