potterton combi 100, problems since draining system

[sartouri]

I have just drained the system to move a rad. When I have refilled the system and turn the hot water on it works fine, but when the central heating is turned on it fires up for about 5 seconds then goes off.

Any ideas? All was fine before.

 

[breezer]

have you bled rads?

 

[sartouri]

Yes, and pressure is up to 4 bar

 

[breezer]

is it a potty puma 100 / 100e? either way, i should bleed rads more, 4 bar is way too high (read that on here), and my potty puma 100e is on 1.5 bar when cold