How to find a leak -low pressure boiler

[hometech]

No its only done it about 4 times in 2 weeks and it's always when we get up in the morning we notice its gone down to 0 (the boiler is off overnight). We fill it up and its back to the correct pressure straight away.

You don't have a leak, you have a situation where air is still being purged. It will settle down...eventually