I hope somebody can help. The boiler has stopped working, I don't even know which type of valliant it is and the landlord is away! I know it has a hot water tank so its not a combi. I also know the error number showing is F28. When I open the front panel there is a red and green light on. When I press the red it goes off and then the boiler tries to start, there are a series of clicks and then it goes off. Please help if you can I am cold!!