Preheat the slow cooker if necessary; see the manufacturer's instructions. Put the apricots, peaches, sugar and boiling water into the slow cooker pot and stir together.
Cover with the lid and cook on high for 3–5 hours, stirring once during cooking and then again at the end, until the fruit is soft and the liquid thick and syrupy, with a texture like chutney.
Warm 3 clean jars in a low oven for 5 minutes. Ladle the conserve into the warm jars. Cover the surface with waxed discs, add cellophane jam pot covers and secure with elastic bands or screw the jar lids in place. Label and leave to cool. The conserve can be stored for up to 2 months in the refrigerator.