On 19/12/2020 09:06, Chris Hogg wrote:
On 19 Dec 2020 08:08:22 GMT, Peter James wrote:

Every three or four weeks I need to de-air the towel radiator in the bathroom.
This is the highest
Radiator in the system.
A friend, who is a retired plumber, suggested that I have a small leak
somewhere in the system. In his day he would have solved it with the addition
to the system of a "leak fixing additive". But he does admit he is totally
out of date and things might have moved on from this.
Can anyone suggest the best way of solving this. I have searched the visible
pipe work, but to no affect.
A Worcester Bosch Greenstar 25 combi boiler is fitted.
Peter

Is it a vented or sealed system? If the latter, is the expansion
vessel doing what it ought to, or is it knackered and the pressure
relief valve is leaking?

But that would show up as a regular need to repressurise, which
hopefully the OP would have reported.

Might it not suggest a system with no inhibitor that is consequently
still corroding?