Central Heating Leaking ? Pressure dropping

Hi there,
Recently our combi boiler pressure has been dropping drastically to the extent that we have to top it up in the morning to have a shower (the pressure has dropped to 0).
So it sounds like a leak somewhere.......
We have now turned the central heating on and have found that one rad does not get hot, not even the pipe that leads to it.
I have turned off all the over rads to try and force this one to get hot with no luck, so seems that the leak must be feeding to this rad?
However when the central heating is on the pressure doesn't drop, is this normal?
Im guessing there is no way around it other than ripping the floor up? (laminate over a concrete floor, copper pipes screeded into the floor)
Any help or advise would be greatly appreciated!

Check that your pressure relief is not letting by, will be a 15mm copper pipe terminating on the external wall by your boiler.

Could also be the secondary heat exchanger is pinholed and letting water from your CH to the hot circuit.

Otherwise leak on pipes...laminate floor should be underlaid with a fibre board, this will prob show dampness if the water has made it that far.

The leak sounds quite bad...in this situation i have heard the sound of rushing water at the rad nearest the leak, if you can at all fill the cold rad this may help pinpoint a pipework leak....then look for signs of damp or start at the rad and dig up the screed and follow the pipe.

I would turn boiler off and let it cool down completely, then set the system pressure to about 1bar, then turn on heating and watch the gauge, if pressure climbs fairly quickly to or near the 3bar mark check the relief pipe outside and the chances are it will be dripping - and your expansion vessel will need recharging.

Agree with twgas,
Had this problem, I had to have my expansion vessel changed, its air valve was letting by. It works like this.
1. Set pressure heating cold.
2. Turn on heating, water expands, pressure cant co anywhere except thro the relief valve to outside.
3. Pressure remains at around 2.5-3 bar (relief valve set pressure) while heating is on.
4. Heating turned off. pressure drops to below initial fill pressure because some water has escaped thro relief valve.
5. You top it up and on it goes..... Back to 1.

The cold radiator is probably due to you keep topping the system up with fresh water that contains dissolved gases. Vent it.

Ps your expansion vessel may not be broken as mine was, it may just need air in with a bycical pump. Some one else will tell you the set pressure and how to do this.