All the bathrooms with mold that I have ever seen have been those with inadequate ventilation.
Do you have proper ventilation?
Hows that S-D boiler?
Tony
i had an electrician in a while back and he said the design of the house meant there was no need to extractor fans as the ventilation was pretty good, you can always feel a gentle breeze in the bathroom!
I'll be looking at the SD this weekend, going to see if i can take apart and clean that flow switch the Chris mentioned. Do you have any tips on cleaning it, or what i should look for to see if its faulty?