combi boiler pressure rising

[jonnybegood]

I have done a search on here and have a part answer to my problem but looking for further advice. A few weeks ago I drained the system to replace a few lockshields, no problems there system refilled and no leaks. Then last weekend I noticed that whilst the boiler was running the CH the pressure gauge was just below 3 bar, its normally around 2 bar and 1 bar when cold. So I drained off to release some pressure back to 1 bar, this has again crept up to 2 bar within 4 or 5 days of using mainly the hot water with little heating. From reading possible causes on here I thought I would knock off first some of the easier solutions, so I started to remove the filling loop (always left connected) and water came pouring out under pressure, I quickly retightened and it stopped.I have checked the fill side (water supply) and the valve is shut, or at least its in the closed position. The boiler side there is a non return valve, but there are 2 things that have me stumped, once I started to remove the filling loop the boiler pressure dropped from 2 bar to 1.5 bar, does that mean the non return valve is passing on the boiler side? secondly as the system pressure keeps increasing does it also mean the fill side isolation valve is also passing? What are the chances that both valves have failed. I could smell inhibitor in the water that came out of the filling loop, is this another sign the non return is passing back from the system or would this be normal? Also I can smell a very faint inhibitor in the domestic hot water, not all the time but perhaps 3 or 4 times over the past 3 weeks. Finally if I do need to replace the filling loop do you guys use the exsting compression fittings on the 15mm pipe or do you replace the lot, just hate removing old olives.

Boiler is around 12 years old and a ferolli 102 - Any other possible causes for the increase pressure or do you think I have found it.
Thanks