Cemline electric boilers feature state of the art solid state step controllers these step controllers have the following features. If you already have a potterton boiler, you will know it is reliable, energy efficient and safe and you will probably want to replace it with another potterton boiler we'd like to explain a few changes we have made to the potterton business since your existing boiler was installed. Ap takes that extra step to show our customers that we respect not only them,.