it normally blows when l turn the heater fan up full, but l expect the overheating is going on all the time. The previous owner had a bypass switch built in, but thats not the answer.

A definite short in that circuit that could cause a fire.Do not attempt to replace the fuse with a larger amp fuse.You can burn out the entire system.Take the vehile to a repair garage that deals especially with troubleshooting electrical problems.Some 'Body Shops' may be able to repair it also as they deal with cars that have been in accidents and need the wiring and electrical done also when restoring the car.

You're right, it is not the answer. it could be the resistor on the switch, but you need a competent vehicle electrician to sort it out properly and you need to do it soon, before you have an electrical fire!

Short circuit. Bring it to a shop and have it fixed.

l think if you are going to own one of these then membership of the Citroen Car Club is a must!

http://citroencarclub.org.uk/

that really is bad luck chap...