41Henrad SE FF - Installation75 HEAT EXCHANGER REPLACEMENTSERVICINGIMPORTANT. Before starting the removal procedure, protect the gas andelectrical controls with a waterproof sheet or plastic bag.SERVICINGHeat exchanger1112. Remove the flue thermostat. Refer to Frame 62.13. Disconnect the boiler flow and return pipes from the systempipework close to the boiler.14. Remove the control thermostat phial from its pocket. Refer toFrame 59.15. Disconnect the overheat 'stat electrical leads.16. Undo the flow and return pipe union nuts and pull the pipes clearof the flow and return bosses.17. Undo the 4 flow and return boss retaining screws.18. While supporting the heat exchanger from below, withdraw thebosses from the flow and return tappings.If necessary, the bosses may be 'jacked' out by screwing theretaining screws into the two threaded holes in each flange.Check the O rings for damage and replace if necessary.19. Lower the heat exchanger to disengage from the flue connectortube, and withdraw it from the boiler.20. Fit the new heat exchanger and re-assemble in reverse order.IMPORTANTThe flow and return bosses are not common and MUST be refitted intheir correct positions.The FLOW connection boss has a COARSE thread.The RETURN connection boss has a FINE thread.Flow pipeReturn pipe16BossesFlow14SupportBoiler8 3 Return 18 1715Refer also to Frame 10 - 'Boiler exploded view'.1. Refer to Frame 58.2. Drain down the system.3. Drain the heat exchanger via the drain point, takingcare to protect electrical components from water.4. Remove the fan assembly. Refer to Frame 53.5. Remove the burner assembly. Refer to Frame 65.6. Remove the gas injection pipe. Refer to Frame67.7. Remove the spark generator. Refer to Frame 64.8. Remove the back retaining screw.9. Withdraw the dry fire thermostat phial from itspocket . Refer to Frame 61.10. Remove the condensate siphon. Refer to Frame74.11. Disconnect the flue gas sampling tube from the topof the heat exchanger.