Leak in radiator pipes

I have a very small leak in my radiator pipes because every 2 weeks or so I have to top up my expansion tank by about 0.2 Bar.Is it possible to put some Leak Fix product into my boiler system bearing in mind that I have a 6 month old condensing combi boiler and I cant locate the exact place of the leak?

What do you mean by "top up my expansion tank by about 0.2 Bar"?

Steam or water boiler? What do you mean by bar? The term "bar" is for a measure of pressure.

I'd not use any leak fix products in my system as it is not a permanent solution, I'd look for the leak. In a steam system, it could be coming out a vent on a radiator and is normal to have to add water.

I assumed he has a hydronic system because he mentioned an expansion tank.

Old radiator valves often leak at the stem and simply tightening the nut on the valve helps, I would not want to add stop leak just because I dont know how it could affect the boiler longterm, as the manufacturer. What pressure is it at on the boiler in lb. Are there any signs of leaks on the relief blow off. If it leaks you probably just have not looked hard enough to find it.

What does a Polish heater look like?

I've actually seen home owners call a steam boiler's condensate return tank an "expansion tank".

If water must be added to a steam system, that means that water and/or steam is leaking from the system. Personally I don't consider that normal, and in the case of our two-pipe (old) steam system, the only time extra water seems to be needed is when blow-downs are performed.

Of course, all the radiator valves have been replaced, and the system is tight enough so that a partial vacuum is drawn when the gas is off. That vacuum lasts a day or two with the boiler idle. --Phil

This is a domestic gas central heating boiler known as a condensing fanned combi. It does not have a header tank and therefore to pressurise the system you fill up the expansion tank with water to a pressure of 1 Bar ( 15psi).The reason I am asking is because I am not sure if you can use a leak fix product in this type of boiler without damageing it