Replace faulty pressure sensor, leaking auto air vent and flue manifold on Ideal Logic 

Diagnosis the fault
Pressure sensor problem because the boiler is not seeing the pressure but if you check the pressure gauge you can see the pressure is good.
Leaking flue manifold and auto air vent
Replace flue manifold, auto air vent and pressure sensor step by step
This video is for GAS SAFE ENGINEERS only, always follow manufacturer instructions.
Before to start any work on gas appliance isolate the power, turn off the gas and the waters.
1. Download manual
www.plumbworld.co.uk/document...
2. Remove front cover
3. Turn off the power, isolate the cold water, flow and return valves
4. Drain the boiler
5. Leave open the drain point
6. Remove condensate trap, flue manifold and expansion vessel to have space to can access the auto air vent and pressure sensor.
7. Remove and replace auto air vent.
8. Remove and replace pressure sensor.
9. Replace flue manifold
10. Refit expansion vessel and condensate trap.
11. Close the drain valve and open the cold water flow, return valves and gas.
11. Re-pressurise the heating system till 1 - 1.5 bar