hi, i have a ferrolli sigma 40-60 wall boiler. the dam thing is driving me mad. i've put a recon pcb,a new water pump, new overheat thermostat switch, a new flow temp sensor,and controller. the problem i have now is switch the controller on the pump runs and the boiler runs. good darts. the boiler gets to the right temp all rads are hot and then the boiler knocks its self off. happy days. after some time the rads cool down and the boiler will not knock its self back on the pump runs contuinuasly. im at witts end with it. im not a plumber or a central heating person. all help or suggestions will be appreted.