How to Fix a small Leak in a Heating System - Adding Leak Sealer 

Thanks, appreciate the feedback, I usually get the magnetic filter cleared out when i get the annual boiler service, but i'll remember to do that before applying the Fennox next time.

It remains in the system by circulating around plugging any small leaks and then just mixes with the water, no harm done leaving in it.

@@HandymanSavage great thanks for reply. I ran it hard for 4 hours just on the rad where the solder ring was leaking and it’s definitely helped. Would have been a real pain to fix properly without making a total mess. Was losing 0.1 bar every few days it’s now been 7 days and no loss of pressure so far.

Not according to this - fernox.com/product/leak-sealer-f4-500ml/#:~:text=Effective%20within%201%2D24%20hours,as%20pumps%20and%20safety%20devices.

I've had the boiler and expansion vessel checked a couple of times, all plumbers said it was a leak in the radiator piping somewhere, but so far this solution has plugged the leak wherever it is. Do you know of any methods to pinpoint where in the system the leak could be? I've had leaks where a patch on a ceiling has revealed the location, but this current leak did not show any obvious location.