Baxi duotec 24 HE whistling from hot water tap even when boiler switched off

[Domesticperson]

Hello,
Our 8 yr old boiler was serviced about 4 months ago. Nothing major was needed.
1) Noticed recently a whistling noise that passes through the hot water pipes when water is drawn.
2) it happens even with Boiler swtiched off (no red display anymore)
3) Not happening whilst central heating is running or cold water is running.


The adey spiratech /magnetite filter thingy was drained and cleaned by the engineer as the last thing before leaving.
Whistling is usually caused by forcing air through a tiny aperture so this could also be a leak entry point for air apparently.
The boiler is working fine apart from that whistling.
Any thoughts please?

[dewaltdisney]

Is the tap valve? They can make a row if the washer is worn. If it is a quarter turn ceramic disc tap then that might not be the reason.

DWD

[Domesticperson]

It happens with both hot water taps.