Pressure creeping up on Vaillant ecotec plus boiler

[dscoll]

Hi

The pressure on my vaillant ecotec plus boiler is creeping up by about 0.2 bar a day with the system OFF.  I removed the grey handles on the filling loop and tightened both valves with a screwdriver, but the problem remains.  Both valves have to be open on the filling loop to repressurise the system, so does this mean that both valves must be, leaking , which seems unlikely, or is it possible just one valve is faulty and if so, how do I find out which one it is? 

Or is there any other possibility?

Any help appreciated.

[TonyT]

The filling loop should not be  left connected in, remove it to eliminate this as a source of the pressure increase

[dscoll]

2 hours ago, TonyT said:

The filling loop should not be  left connected in, remove it to eliminate this as a source of the pressure increase

I see, thanks. It's an internal filling loop, can I  just unscrew it with the boiler on?

[dscoll]

I tried to remove the filling loop at the CH flow end as suggested but water came out under pressure. How to I find out which bit is leaking:

filling loop

CH flow valve

cold water mains in valve