Ideal Elan Fuse blows when switched to High

Hi All. Please can you help me with a problem with my Ideal Elan boiler. During the summer I have had it switched to the low setting however now it is winter I have switched it back to high. The problem is that when I switched it to high it blew the fuse. I changed the fuse and it blew again. I changed the setting to low and replaced the fuse but this time it was ok. I tried to switch it back to high but it blew the fuse again. The boiler is now running on low but I would like to sort this problem out as I believe the house feels colder on the low setting. Do I need a service engineer or is it something I can do my self? Thanks Terry

What does the high/low switch connect to? If you can answer this question, you can possibly repair it yourself. If you can't answer the question, you definitely need to get a boiler engineer in.

I had the same problem on a thorn apollo it was faulty wirring on the high stat it had burnt out and was touching the heat exchanger. 3amp fuse kept blowing so fitted 13 amp and wires sparked showing were the fault was. Some heat resistant cable and ceramic cable connecters and the job was done