Boiler Pressure Keeps increasing - Vaillant Ecotec Plus 838

[Zishan]

Hello everyone,
I have a Vaillant Ecotec Plus 838. The issue i have is after the heating is switched on and then left it to cool over night i see the pressure has gone up.
For example yesterday it was set at 1.3 heating was switched on and when it reached its temp it went upto 1.9 so no issues. But when its left to cool over night the pressure shows 1.8 in the morning. The pressure in the expansion vessel was at 1.0 bar and when checked this morning its at 1.5 bar. The expansion vessel was replaced yesterday.
I have been monitoring this for weeks and everyday letting the pressure out.
Why is the air pressure in the expansion vessel going up ? is there another part to replace?

If you require any info from the boiler please let me know and I will get them for you.

Not technical at all with these things so please be gentle when replying.

 

[ShaunCorbs]

Filling loop passing ?

 

[snowhead]

The expansion vessel air pressure needs checking with no water pressure acting on it.
You can't compare the vessel air pressure if the water pressure was 1.3 then 1.8,

 

[Zishan]

ShaunCorbs - thank you for the advise. this is a internal filling loop so i have disconnected the left side of the hose (looking at front of the boiler) and i can see water dripping out, i guess its coming from main water (which is on the right side).
I will monitor this and see how it goes. I really hope this is the issue.

Snowhead - thank you for the advise. will keep that in mind.

 

[Deleted member 120897]

If you’ve had a new vessel, it doesn’t rule out a blocked communication pipe. Are you checking the digital display on the front when the pump has kicked in?

 

[Zishan]

If you’ve had a new vessel, it doesn’t rule out a blocked communication pipe. Are you checking the digital display on the front when the pump has kicked in?

Chris - can you please elaborate what should i check on the display when the pump has kicked in?

 

[EvilDrPorkChop]

Common issue with these, is it about 10 years old? The filling links start to pass.

 

[Zishan]

Common issue with these, is it about 10 years old? The filling links start to pass.

EvilDrPorkChop - I moved into this property and i was told this boiler was installed in 2018 when they did the extension. Its a pain to work on as the boiler is installed in the loft near the ground and not like shoulder height like most boilers ive seen.

Everyone - can someone explain the procedure to replace the filing loop valve on this boiler - what the procedure?

Is it called a water inlet valve that i would need to purchase?

 

[John.g]

ShaunCorbs - thank you for the advise. this is a internal filling loop so i have disconnected the left side of the hose (looking at front of the boiler) and i can see water dripping out, i guess its coming from main water (which is on the right side).
I will monitor this and see how it goes. I really hope this is the issue.

Snowhead - thank you for the advise. will keep that in mind.

If the boiler is/was off overnight for 8 hrs then the filling loop would have to pass ~ 1.25L, 156ml/hour, to increase the pressure from 1.3bar to 1.8bar assuming a 8L E.vessel.

 

[Deleted member 120897]

Chris - can you please elaborate what should i check on the display when the pump has kicked in?

I think I didn’t explain it well, you say that the pressure is increasing and wondered if you were reading the digital display, especially when the pump had kicked in.