When a boiler is turned off some heat remains in the mass of the boiler. If the flow through the boiler is stopped at the same time the boiler is shut off, the residual heat is lost. Therefore, after operation of the boiler the residual heat in the boiler should be purged to the system in order to decrease standby losses. This is accomplished by turning the boiler off but keeping the system pump on for a period of time. This function increases system efficiency by minimizing standby losses.