Radiators not heating up with Istor boiler.

I have turned thermostat to max but the boiler just wont pump out warm water to my radiator. I have hot water and I have bled ALL my radiators. I had a similar problem before, when I had thermostat to almost 0 degrees during summer and when I turned it back on in the winter I had to wait 24 hours for the heating to kick in.

But this time I have had the thermostat at a constant 10 degrees just in case. But it still doesnt work. I have tried to get heat for 2 days, but radiators are cold.
At one point i could feel the main radiator getting slightly warmer on one side, but quickly disappeared.

Why did you bleed the rads?

Whats system pressure?

When was boiler last serviced? Best done during summer ready for winter!

Tony

I asked around for advice and was told to bleed radiators. As soon as I turned the valve water started gushing out, so that was pointless yes. Pressure says 1.5. Service was 2 weeks ago...