Several problems
1. Having to constantly fill the system with water as it drops below 0.6. It also drips out of prv. (The problem was worse when the boiler was on timer to start with, so it was switched to constant which sorted the problem, now its just the same on constant)
2. Only warm water as the burner cuts in and out while the hot tap is being run

Mark25, February 2010

If Pressure of Central Heating is remaining below 3-Bar in Pressure, then the PRV needs replacing. Also if the pressure is at 0.6bar then your Domestic Hot Water will not function correctly, due to a pressure sensor lock out.

Other items to check would firstly be the 3-Way Diverter Valve, and if these prove to be working correctly, check the Domestic Heat Exchanger is not blocked or furred up. There is a Filter on the Cold Inlet which could also attribute to reduced hot water if it is blocked in anyway.

If the burner continues to cut out, you will need to check the Hot Water Thermistor, Fan Unit and Air Pressure Switch for correct operation. Really I would recommend that you contact a Gas Safe Registered Installer who will have the necessary tools and test equipment for diagnosing such problems.

Hope this helps.

Anthony, May 2010