My polo 1.0 se’s Blower would only work on number 4, so I did some research and discovered that it was the heater resistor. I replaced it and now the blower works on all 4, however there is a fishy burning sort of smell when the blower is on either 1,2 or 3. I wondered if anyone knows what the cause of this is and what I should do? 

Usually that smell is a glue somewhere in the dash vent system or could be on the resistor

Some plastics give off the smell as you describe when they are heated.

If the resistor pack that you fitted was NOT genuine VW, I would suggest that you check that there are no signs of overheating on it, as there is a possibility of a fire risk.

Hopefully it will be OK and it is just preservative that is burning off BUT it would be advisable to check.

 

Regards