is a one pipe central heating system suitable for a combi boiler

I agree we the previous poster. Modern combi boilers are designed to operate on a two pipe system (flow & return) in a single pipe system the heated water will return back to the boiler to hot so therefore this is a very inefficient waste of energy and also your boiler temperature thermostat will recognise this and constantly turn off the boiler until a certain temperature drop has occurred then begins the re-heating process or will constantly be in a situation we call permanent modulation where the burner flame will always be low due to the higher then normal return heating water temperature!

A one pipe system is ok for a combi boiler although it does have pitfalls. The last radiator in the loop will generally be cooler than the rest as the heat has sufficiently cooled throughout the run. Modern boilers require a constant flow rate so any blockages will cause the boiler to overheat and cut out fairly quickly. Best advice is if possible changeover to a two pipe system as it's more modern and efficient by means of feeding all the radiators equally, plus you can fit a filter on the return to remove any debris from the radiators before it gets back to the heat exchanger.