I've got a Valiant model too - ours goes on 0.6 bar sometimes too. It means that the pressure is too low, and needs to be increased for the system to work more effectively. If the pressure continues to drop, it'll eventually stop working automatically, and an error code will show on your thermostat unit attached to your lounge wall (or wherever you've put it). There should be a pressure dial with a 'hand' on the front of your boiler system - it'll probably show the hand is below a 'notch' (gap) in the grey area of the dial? The hand needs to be positioned just above the notch in the grey area.
What you need to do is turn the lever VERY SLOWLY on the pipe underneath the system - hopefully you have access to it! When you first look at the pipe, you'll see that the lever is at right angles to the pipe (in the closed position). You need to VERY SLOWLY move the lever and watch your pressure dial 'hand' move slowly up towards the 'notch' (it's white on my system) and a little bit into the grey area. Then immediately move the level back to its original position on the pipe so it's at right angles to the pipe - and you can't move it any further, so it's closed properly.
During the autumn / winter it may happen a few times, so just keep looking at it now and then.
Wait a few minutes, and you'll see the temperature on the gauge change to 20 etc...
Hope this helps - feel free to write a message again if you need further help....I'll check it again :)
Rosie, October 2013
