Hi, new on here. Been having problems for few weeks, sometimes heating will come on, sometimes won't. Had central heating engineer to come and fix it and service few days ago, it was full of dirt. It was working when he left, cannot get heating on this morning, It has been working on and off since engineer been, was working last night. I don't know if it's a problem with the Drayton Digistar+2 thermostat controller. always got it on the manual setting. The boiler fires up when I turn hot water on, otherwise it's hit and miss. I've fiddled with the Digistar, changed batteries, cleaned it. I saw advice to sand battery contacts which I did other day and it started working, sometimes the heating would come on after I've fiddled with the Digistar. The green light is on, on the box next to boiler. Is it the Digistar controller or the boiler. Any advice welcome please. The central heating is about 8yrs old.