Expansion vessel pressure

[NorfolkandGood]

Hi,

Due to a suspected fault with my E.V. I got a replacement one but now it's arrived it turns out it's pre-charged to 1bar and the one I'm replacing is pre-charged to 3bar.
Do I need to swap it for a 3bar unit or will it be ok?

 

[twgas]

depends what it's on.

 

[kitch0978]

don`t think your old one will be charged at 3 bar!! wat system you got?

 

[gas4you]

I assume you mean an expansion vessel for an un-vented HW cylinder?

 

[NorfolkandGood]

Sorry, should have explained what it's on.

Unvented CH system. Checked pressure the other day using tyre gauge and it's showing 2.7bar.

 

[twgas]

I assume you mean an expansion vessel for an un-vented HW cylinder?

I'm thinking you're right for the existing, but he may well have bought a heating system one.

 

[uknokianut]

What is your system pressure going to be ? You should set the vessel pressure to 0.2 bar above the system pressure .
So if your boiler will be topped up to 1bar , the vessel should be at 1.2bar.
Make sure its not connected to the system when you pump it up .

 

[Agile]

Its questionable if you should even be changing the EXV without the unvented qualification.

The simple advice would be to increase the charge pressure to 3.0 bar if thats what the cylinder instructions require. Is this replacement white or red ?

However, the advanced advice would be if the existing EXV is showing a pressure of 2.7 bar then why on earth are you changing it when it seems to be fine ???

Tony

 

[uknokianut]

Sorry, should have explained what it's on.

Unvented CH system. Checked pressure the other day using tyre gauge and it's showing 2.7bar.

He is saying its for an Unvented central heating system. Not unvented cylinder.

 

[NorfolkandGood]

I'll give you the full story so far..

Woke up one morning and house was freezing and no hot water, checked boiler and pressure was down to 0.5, re-pressurised to 1.2, ran CH and HW cycle and worked ok. When cycle had finished the boiler pressure dropped to 0.5 when system cooled. Have been repeating above procedure since last weekend with same result. System pressure remains at 1.2 when left not running but drops to 0.5 after cycle has run. Noticed seepage from PRV outlet pipe outside when system is running. after going through previous discussions on this forum related to similar problems i suspect it's either a faulty PRV or the expansion vessel, rightly or wrongly I've opted to change the EV first, (it looks easier to replace than the PRV), lazt I know but i gotta start somewhere.
The EV fitted in airing cupboard is 12L and the label states pre-charged to 3 bar, the one I've just had delivered states pre-charged to 1 bar and states not allowed to exceed this.

 

[twgas]

However, the advanced advice would be if the existing EXV is showing a pressure of 2.7 bar then why on earth are you changing it when it seems to be fine ???

Tony

I believe most of the pressure vessels that are changed are not at fault but the people checking them don't know what they are doing.

 

[uknokianut]

Well that one will be ok then. Top up your system to just under 1 bar and all will be fine with the EV. Now to see if your PRV is leaking.

 

[NorfolkandGood]

Agile,

The one that's in is grey and the one I've bought is red, what does the colour mean?

UK,

Thanks for the advise.

 

[Agile]

Your existing EXV seems to be fine!

But its just not set at the correct pressure!

Open the CH system to atmosphere and then REDUCE the charge air pressure in the EXV to 0.9 Bar.

Then repressurise the boiler to 1.5 Bar cold and all will be fine!

I have seen a PRV fitted by BG which was left at the supplied pressure of 3 Bar. That stupid mistake resulted in me being called and the customer having to pay our charge when the fault was the BG engineer's fault !

Even more surprising was the EXV that BG had fitted as an external when the one in the boiler was also OK but just had a blocked communicating pipe in the Puma 80.

Tony

 

[NorfolkandGood]

Agile,

Just to be clear of your instructions, open the drain under the boiler and then reduce the EXV, close the boiler drain and repressurise boiler to 1.5bar.
Not sure what PRV is set at, boiler book states max pressure 3bar but not sure what the fitters set it to. Have noticed that boiler pressure doesn't seem to go above 2.5bar when running though. The boiler is Glowworn 18si and book says it's got a EXV internal set at 0.5bar, but all my neighbours seem to have same set up with an external EXV also fitted in airing cupboard like mine is, (all houses in the estate built by same company)

Not sure if this info helps.