I have had a Titan Flowmaster Indirect 300litre unvented hot water cylinder for about 2 years now and it has worked fine until about a month ago. Previously you were never aware of the cylinder drawing in water, but recently it sounds like it's drawing water numerous times a day, in bursts of 10 or 15 seconds. The sound is identical to that when you turn the main stop cock on and water rushes through the system. I have checked the following
1. No detected leaks from hot water cylinder, or overflows
2. No other water leaks detected
3. All radiators bled
4. Preesure on the system running at about 2.5 bar
The pressure from the taps and temperature of the water is unchanged and nothing on the system has been altered. The water take on seems completely independant of use, for rxample it can happen several times during the early hours of the morning, when there has been no heating or water use for several hours.