My boiler needs topping up every few days there are no apparent leaks in the system. the only clue is the pressure relief valve blows off thus discharging the water. Could it be the directional valve that is faulty

Norman, January 2016

Another alternative is that the pressure release valve is faulty. I had both problems at the same time on my boiler a few years back:
1. Pressure release valve was not working (you could blow through it) - replaced
2. The Schrader (tyre) valve was faulty, but the expansion vessel itself was okay. Replaced the valve and re-pressurized the
expansion vessel.

Adrian, January 2016

Raise the pressure to 1 bar while system is cold then heat up and watch pressure if it rises to 3 bar the expansion vessel requires refilling or replacing

toptrish, January 2016