Hi, i am having problems with my valliant combi boiler. not sure of the make/model- was already in the house when we moved in- was installed about 4-5 years ago. hot water is fine, but having problems with central heating. it turns on fine, but after a couple of hours it turns itself off. i wasn't sure if it was because it can be put on a timer. we have to click 'once'/'twice'for it to go on the timer, but can turn it on when we need it by pressing 'on', but when clicked 'on' it turns itself off. any ideas? 
