Checked with Directline, which I am with at the moment, and they can't cover for waterfed pole systems or hot systems, because the system doesn't have it as a listed modification, so by default their underwriter(s) don't insure if you have a wfp system fitted. They used to have a mobile cleaning modification in their system, but no longer.
Funny enough the first time I checked with them they never even heard of it, and couldn't quote me, so I just didn't bother again. Thought I should really get this checked out again because of going hot.
So who are you with for your insurance? I've always found Directline to be the cheapest for me personally, but seems I have to change to be able to stay insurance. Great.