its a couple of years old but over the last 2 months have been having problems with HW and CH when you switch it on to HW it makes a strange rattling noise but fires up (most of the time) but recently had no problems with HW for the last 3 days then today i go and switch CH on and within 20 mins it goes off presto no CH and no HW someone suggested that it could be the thermocouple that needs replacing.its a combi gas boiler. hope someone can help my kids bedrooms are freezing