We have a Heatline combi boiler C24/28, we had a frozen pipe on the outside tap, everything was fine until then, now the boiler works for central heating but the hot water is only luke warm then goes to cold and the boiler switches off. We have found that the water will stay hot if we put the cold water tap on. Someone has suggested that it could be the Domestic hot water sensor but they are only guessing and said we should replace this first because its the cheapest, but we don't want to spend loads of money with trial and error replacements. There are no flashing lights on the boiler stating problems. everything is work other than the hot water. We have had a heater on it just in case it was frozen but still remains the same. Condensing pipe not frozen either.