Daughter moved into a house with a Sime super 105 mk2 boiler. she had to have some plastering work done, so I removed a radiator. Whilst I was there I checked the boiler and saw water pressure was almost zero. Not being familiar with the boiler I couldn't see where the filling loop was, so said I'd look for the manual on the web. Meanwhile two days later she phoned me to say the pressure had suddenly gone up to 3 and the pressure relief valve had opened. I went round to have a look and sure enough it was at 3. I bled a rad to relieve the pressure and asked her to keep an eye on the pressure. I can't understand how the pressure has increased unless the filling valve is not fully closed. Any ideas on this?