Bad cold start and glow plugs light flashing.

Hi

I bought the car 4 months ago since then the glow plugs light has been constantly flashing(80% flashing, 20% not).
I changed glow plugs last month.
Car will start in 5-20 seconds of ignition in 0 to -10 celsius. Or won't start at all without easy start.
Car will start in around 5 seconds when outside temperature is above 0 celsius.
The warmer outside temperature is the faster it starts.
When car is warm it will start in around 1 second but never immediately.

I went to diagnostics once as well, throttle valve got changed and there was one unknown fault.

Car: Honda Accord Tourer 2005 CDTi

What could be wrong?

Flashing glow plug light is normally low fuel pressure or low boost pressure, not faulty glow plugs. Have another diagnostic carried out

Change the fuel filter, make sure it's a Bosch