The fan in the car heater has no connection with the hazzard relay.
If the fuse for the indicators/hazzard is ok, follow wire along to the relay, see if power still good on that wire, the stalk is after the hazzard/indicator relay, so if ok up to relay, but blows once the indicators or hazzards are put on there is a short to earth on one side, try the indicators to determine which side, then remove each bulb in turn and try again, if it blows it is the wiring between stalk and indicators on the relevant side, if it doesn't replace one bulb at a time and try, rarely but does happen a bulb can go duff and short out inside.
tabetha