Philips Perfectcare GC 9220 takes ages to produce steam

Problem description:

After the device is turned on and heated to operating temperature, the trigger on the iron does not release any steam. But if I keep waiting for approx 1h, and meanwhile preventing the iron from turning off by pressing the trigger like every 5mins, suddenly the device starts to work normally.

Parts already changed:

Complete pump assembly with hoses and valves all the way to the boiler. Descaled with mild citric acid.

It's like some component benefits from indirect heating from the boiler and starts to function after a long period of time.