Hi all. i have a heatline vizo 24. It packed up the the other day. It started making a clicking noise and then lost all power. Turned out it was a dv valve and blown fuse on the board. Also when the chap came to fit new parts he said there was low gas pressure. So transco has been out and fitted new part to my meter. Now when using hot water it makes a humming noise (like small airplane) going low to high pitch while using hot water. Any idea's??