How can I isolate a leak in my central heating system?

I have a leak somewhere in my oil fired central heating system (open system). To prove this I tied up the expansion tank ballcock in the attic and marked the water level (all done when the system was cool). I then turned on the heating and used it for one evening (approx. 4 hours). The next day when the heating system was cooled I check the water level in the expansion tank and it had dropped over 1 inch. Which means there's a leak somewhere.

What I want to know now is, is it possible to isolate where the leak is in the house?

blueharvester said:

Is it possible to isolate where the leak is in the house?

Click to expand...

Yes with a iso valve when you find it. Better to fix it right away though.

Repeat your test a couple more times. If the level is constant one - it will be contraction /expansion within the system. If it continues to drop - then you may have a problem

Turn the system off and let it cool.
Surface leaks can go undetected with the boiler running as they just evaporate off.

Check all compression joints. Radiators, circulator unions, boiler connections , bypass valves etc and also check the pipe work.
The heavy frost earlier in the year may have fractured or damaged a pipe.