What literage is the pond Steve ? I'll give you an example with mine. My pond is about 1500 litres, the pump can move 5000 litres an hour and the filter can cope with 10000 litres an hour. Nothing is stressed and nothing is working anywhere near capacity. If that pond is 8ft mate that pissy little filter / pump is nowhere near enough. Work out the literage, get a pump that can handle double that and get a standalone filter that can handle the volume of the pump. That one isn't up to the job and thats why they're burning out.