cooler end of recuperator heat transfer surfaces the invention utilizes residual heat from the engine at shutdown to clean the recuperator referring to fig3 the gas path cleans itself at between approximately 800 u00b0 to 1000 u00b0 f preferably between approximately 800 u00b0 to 900 u00b0 f during an engine shutdown the temperature profile through the recuperator is approximately 1200 u00b0 f in and 500 u00b0 f out the residual heat equalizes in the system on shutdown so that the recuperator core is at approximately 700 u00b0 f raising the temperature in the recuperator to the self cleaning temperature preferably 800 u00b0 to 900 u00b0 f is accomplished in the invention by one or more of the following 1 blocking the exhaust to reduce heat loss and thereby increase heat transfer to the recuperator 2 inducing an air flow with an air pump to convection heat the recuperator core from the residual heat in the combustor engine core and hot parts of the recuperator and 3 use of an electric heat probe electric tubular heater or gas propane torch inserted into the recuperator inlet plenum blocking the exhaust is especially effective in an add on system such as a cogenerator where the block exhaust is easily accessible use of an air pump is effective particularly in that the air pump already exists on.