No hot water coming from the boiler?

I hope someone can help. I had a small leak in my kitchen which was easily repaired but the mains water had to be turned off. Now that it has been turned back on my Saunier duval f23e combitek boiler is not firing up when the hot water taps are turned on. Hot water is produced when the heating is switched on but not when the demand for just hot water is needed.

The pressure in the boiler is at 1.5bar which is correct. When the taps are turned on you can hear it whistling through the pipes and the water pressure seems fine from the taps but no matter how far I open the hot taps the boiler does not fire.

I would be grateful for your guidance.