Had a problem with my Feroli Optima 701 - the hot water was working fine but the central heating was intermitant, the radiators got luke warm and then would cut off completely after a couple of minutes. I called many competent engineers who fixed the problem temporarily for a few weeks. Eventually he said 'change the boiler', which is usually said anyway. I had no means to change the boiler due to the cost of it. Eventually i found that the central heating termostat was conducting too much heat and gave a cut off signal to the boiler. I took the thermostat out and cleaned the connectors with WD40 and its housing. To reduce the heat conductivity i put a thin piece of plastic ( i cut up disposable plastic cup) under the heating thermostat and put back the red and green connection wires. My heaters are now boiling hot as is the hot water. I saved many pounds by not going to these cowboy engineers.
This method should work with any boiler.
This method should work with any boiler.