Hi ree, I too have one of these Potterton suprima boilers. I had some problems with it last winter. It was cutting out and generally acting funny. I did some internet searching about it to see if it was a common problem. I was shocked to see all the hassle associated with them!
There was even a [broken link removed]) campaign about them. Anyway my one was exhibiting the classic symptoms that others seem to complain about so I found a few online forums with a few suggestions on how to fix them.
I am NOT a DIY expert, it takes me 20 mins to change a plug. But I figured I'd give it a go - I would imagine that most people will tell you not to tinker with your gas boiler and they are probably right but this is my experience of what I did.
The Potterton forums that I looked at suggested that there was a problem with the soldering on the circuit boards of the unit. They suggested that there might be scorch marks on a faulty board - sure enough there were some on mine. The recommendation was to identify the weak connections and resolder them and then to remove any dust/dirt that might be present. The whole soldering approach was well beyond my means so I just went for the dust/dirt removal part. It did the trick. No problems since then, touch wood. However I am resigned to the prospect of it going again in the not too distant future.
On the positive side, from your point of view, I would imagine that Potterton might have responded to any negative press from their older products and would have made some improvements with newer models? So one might hope that the units that plumbers are installing today are superior to the one that I have...