I moved into a flat about 2 months - over the past few weeks every time I run the hot water (in any room), it smells of burning rubber.

I haven't changed any settings or touched the boiler. Any ideas as to what this may be?

Bacteria in the water reacting with the anode rod can produce a "rotten egg" smell and make your water taste bad. To correct this problem you must change the old magnesium rod for a aluminum one. Then you must drain and flush the tank and flush out ALL the hotwater lines. You must also remove and clean ALL aerator screens. TIP: Leave one intact so you can put them back the same way. They will not work otherwise. The anode rod is located under the large hex nut on top of your heater. If you need instructions on how to flush your heater, click on back. Hope this helps and thank you for rating my reply. TOM
FUQuestion : The water really doesn't have a rotten Egg smell. It's hard to describe but it's more like plastic. Could this still be caused by the same thing you described?
Answer : Then I would check the dip tube. That's a plastic tube located under the cold water inlet on top of the tank. If it starts to deteriorate it would cause the problem you describe. Pull a areator and check the screen. If you find white flecks on the screen then you must replace the dip tube and flush out the tank, hot water lines and clean the screens on your areators. Even if you don't find any white flecks, that's the first place I would check. Shut down the water and power source and take out the 3/4" male adaptor from the cold water side. You should see the collar holding the tube and be able to pull the dip tube up for inspection. Replacement parts can be purchased at Home Depot or a plumbing store. Good luck. TOM