Never encountered this before, but hear it's not uncommon. I'm in a flat, there's little room for head, so water pressure relies on a pump, which is now dead. Seeing as I'm looking at £300 to replace it with a decent on, I started wondering about going over to mains pressure, but I'm electric only. I'm a decent plumber, loads of experience with pipework, central heating etc, but I've not done unvented before. Am I right in thinking that it needs certification and can't really be done DIY?