How easy is it to remove the valves from a heated towel rail?

I have a heated towel rail with angled valves. The valves protrude from the wall and mean that I'm not able to pull my washing machine out for maintenance. I've removed the caps from the valves by simply loosening the grub screws; but this only gives me an extra 5mm wiggle room (not quite enough!) If I could remove the valves themselves from the heated towel rail, the washing machine would just slide out without any problems! Even removing one valve would help enormously. But how straightforward would this be..? Would I need to drain the whole system or anything like that..? Appreciate any wisdom...