Worcester, 24cdi Combi, drip from flue

[warehouseman]

Have an old 24cdi which until recently has done well but 3 months ago a new Expansion Vessel was fitted. All was fine until a couple of weeks ago when I noticed the pressure was down to about 0.50. I topped it up to 1.25. Everything's working alright but today I spotted the external flue dripping very slowly for a minute when the boiler first started. I assume this is why the pressure is very slowly going down. It's down from 1.25 to 1.00 in 10 days. I'm no expert but am wondering if it's to do with the previous EV being fitted. Or maybe the PRV, although it rarely goes above 1.5 when both hot water and CH is being used. Any ideas welcome.

 

[ShaunCorbs]

Would say it was water vapour from the cold weather we've had

 

[heatservice]

Your loss of system pressure could be down to a leak, have you checked to see if the PRV warning pipe is dripping, just hang a small container on it and check it after a few hours.

 

[warehouseman]

Your loss of system pressure could be down to a leak, have you checked to see if the PRV warning pipe is dripping, just hang a small container on it and check it after a few hours.

Thank you for the advice. I was getting confused and thought the PRV pipe came out behind the flue!
I've seen a bendy pipe lower down which I presume is the PRV . Don't think it's been dripping but will take your advice.
I'm wondering if the small amount of drips from the flue is just vapour as someone has suggested. This is an old 24cdi RSF so I presume non-condensing. Is there ever a situation where water can come from this flue?
I'm still suspicious about the Expansion Vessel that was put in a short time ago as the previous one packed up and the pressure dropped to zero in that instance.