Yes that is what I am guessing, that is why I am asking if there is an engineer who speicalizing in old boilers as I hope he might know to find the part and service and fit, I am not in possition to change the boiler at present moment.
I need help if there is a engineer in South Bucks area who would service my old Potterton Netaheat 16-22. It looks like thermostat or heat exchanger not working.