halstead quattro problems

Wonder if anyone can help me. Went to put the heating on the other day and noticed the attic radiators were not coming on. Checked the pressure and it was down to 0. Fed some water into the system and everything seemed ok. Then noticed that the boiler was venting water outside, which had never happened before. Released all the pressure and started again.
Now there is no venting of water and all the radiators work fine but the pressure goes up to 1.4 when on and then goes back to 0 when off.
Is this a problem with the gauge giving me an incorrect reading.
Thanks

No, probably the internal pressure/expansion vessel. No air left so nowhere for the water to expand to. See Boiler Pressure Problems in the faw section.
The empty rads were the expansion space until you went and bled the air out!