Hot Water but no heating Alpha 240P

[jpv76]

My Alpha 240P combi boiler works fine for hot water, but I can't get my radiators working.

When I turn the boiler on to "Water & Heating", the thermostat does trigger the boiler into action, but after a few seconds, it stops.
Also, pressure has built, and the gauge shows it to be well beyond the "green zone". I've tried bleeding the radiators, but after a semi-second of hissing, nothing happens (i.e. no air or water leaves the radiator).

I'm new in to the flat, and have never worked the heating system before - anyone have any ideas?

 

[namsag]

Check isolating valves under the boiler are not turned off and that the rad valves are open

 

[jpv76]

Thanks for the quick reply.

The radiator valves are open, but I think I need some help on the isolating valves.
Under the radiator, I can see one isolating valve with a plastic lever- this is in line with the pipe, so I presume that it is open.

I wouldn't know how to check any others however, as there are no levers on them?!

I'm new to all this, so please excuse my ignorance!

 

[namsag]

Think on these the one with lever was the gas.. On the two outer pipes(22mm) each side there may be a line in the valve nut this should be in line with the pipe(not across it)