I had a British gas engineer round to look at a vaillant boiler which was producing fluctuating hot water. He said the heat exchanger needed replacing but refused to do it because there were mouse droppings inside the boiler (visible when he opened the front panel to look inside). He said I had to get a certificate from rentokil proving it "rodent free" before he could do the job. I took a look after he'd gone and it took about 40 min with a sponge and some bleach to sort it out. It seems unreasonable to me that bg would refuse to do this work, has anyone else had experience of this sort of thing?