Boiler pressure keeps dropping. No leaking

[jcaan]

Hello guys

I hope you're all well.

Every Couple of days I need top the pressure of my combi boiler... it always drops.

There's no obvious or visual leaks around the house.... what can this be ?

This has been going on since last year.

 

[picasso]

Boiler make and model ?

 

[Mike13]

It could be the expansion assembly has lost its air and the pressure spike each time it heats causes a vent to outside? tie a plastic bag over the pressure relief vent and see it it collects any water each day?

 

[terryplumb]

Does pressure rise to around 3 bar when central heating is in use ? If it does water would be expelled from the pressure relief valves pipework.
If that isnt the cause ,and there are no leaks from the system,then the heat exchanger may be leaking and water loss through condensate drain.