Boiler System Leak and Isolation

Ish20

Hello,

I am seeking some help and advice about loss in pressure in my heating system. The house has a 5 year old Ideal Logic 35 boiler. It recently had a change in the water pump (2019 October) with a total fluid drain in the heating system. The pressure was stable till about February 2020, when it had to be topped up because it dropped to 0.6-0.7bar. 
Since then it needs topping up every 2-3 weeks, because the pressure drops by 1bar in that period of time. 
Unfortunately I could not get anyone from the company to come out and diagnose it because of the current Covid 19. 
There are no visible leaks anywhere on the radiators or any dripping in the actual visible part of the boiler or underside. There are also no visible leaks anywhere on the ceilings or walls. The boiler is losing pressure in what looks like a linear response, because there are no sudden drops in pressure when certain things are turned on. My reasoning is that I DON'T think that its the heating piping in the walls because its only a 5 year old house (hopefully not), but then I don't know what could be leaking on the boiler with no visible sign.
I would like to ask how it would be possible to isolate the boiler for overnight to check whether its the boiler at fault or the system?

Undervalued

That is a tiny leak! 

Most likely, as the system was worked on, is that it is either a small weep from one of the joints that was disturbed (either end of the pump) or it is coming from the pressure relief valve.

Sometimes when the  PRV is used to drop the pressure, to work on the system, a tiny bit of grit or sludge from the system gets trapped in the valve. It will have a pipe to the outside, probably open ended just above ground level. If you can find that pipe put a small pot under it and see if there are and drops of water in it the next day. Sometimes blasting a bit of water through the pressure relief valve then letting it snap shut will make it seal properly - or it could make it worse but at least you would know where the problem is!

Ish20

Ok great, thank you.
So if there is a pipe outside somewhere through the wall, (I am guessing it doesn't have to be where the boiler is) then watching that might solve the problem. I can't do anything about the pump, when the whole lockdown ends then an Ideal technician will come to check it out, but till then I guess I will have to fill it up. 
What is strange is that everything was alright from October 2019 till February 2020.

Ish20

Also I just wanted to ask, How much water do you think I could be losing, when the pressure drops 0.5bar?

Undervalued

Ish20 said:

Also I just wanted to ask, How much water do you think I could be losing, when the pressure drops 0.5bar?

Surprisingly little. Maybe a coffee mug full!

Ish20

Ok great, thank you!
thankfully that's not a lot. 

Thank you for the help!