Potterton PUMA 100 - must be a simple explanation?

Low Pressure problem in PUMA 100e

I bled the radiators in the loft room three days ago. Since then, when the boiler goes off, the pressure drops and the red LED comes on. Means the boiler will not start again.

Recharging the system with water from mains means the light goes out and the system will start.

What do you think? Keep charging it and finally it will settle down again, or is there a more fundemental problem.
Has anyone had a similar problem - did it sort itself out?

I have checked that the radiator bleed valves are closed and there don't appear to be any leaks in the radiators or pipes.
Thanks for any advice.

The air/nitrogen pressure of your expansion vessel may be low (or the vessel could be too small for your system). The central heating water expands as it heats up. If the vessel cannot handle this expansion, then the water pressure will build up until the pressure relief valve opens (at about 3 bar), releasing some of the central heating water.

The air in the radiators in your loft room acted as a supplementary expansion vessel. Now that it's gone there is nowhere for the water to expand to. Introducing some air into a radiator (by partially draining it), in a room that you do not use much, may alleviate the problem - until the boiler can drained and the expansion vessel checked and recharged.

For more information about expansion vessels, click here.

This does seem logical and does seem to explain the problem.
Thanks for the assistance.