I have an Ideal Combi 24 It is in a house I rent out. The tenant recently left and so when I went into tidy and get ready for new tenants I found that I could start the boiler and it supplied hot water on the winter setting but the radiators are completely cold. I cannot check with tenant if it was OK before( He has gone back to Libya) I have made sure all radiators are open . Any ideas for a remedy? There is no error message on the control panel.