External pressure vessel

[PCatterall]

My sons boilers pressure vessel was leaking at the air valve. We understood that the 'simple' fix was to get an external vessel fitted and there was room for one below the boiler. He could not get a local plumber to fit one so after reading and watching a video we thought we could do the job our selves.
We bought the vessel and all the bits and pieces.
We noted that we could feed a flexible 10 to 15mm pipe up through the boiler to the existing feed to the original tank then pipe down to the tank fitted below the worktop.
We drained the system and connected up the new tank. We recharged the system and all seemed to be going well .
However when we tried the boiler it initial started to work then the pressure rose to 3 bar and the system started knocking and we shut it down ( there seemed to be knocking noises from the tank itself.
The tank has the correct air pressure. As we had simply replaced one tank for another of the same side we can not understand what is happening.
I did wonder how the water was initially going to get into the tank as ( to start with there is air in the water side and the pipes) I cant understand how that air is replaced at the initial charging of the tank.
Can anyone advise please?

 

[dcawkwell]

Sounds like the water isn't getting to the expansion vessel.
Perhaps a blockage that would be the only cause of pressure and banging noises.

If all the problem was that the tyre valve was leaking in the pressure vessel all it needed was a new 20pence valve from the local
car spares place. Sorted.

 

[Steelmasons]

Fitted an additional 25 litre vessel to a WB 30 cdi today , hard plumbed into pipework below boiler , works a treat.

What size vessel did you purchase although I have a pretty good idea.

 

[45yearsagasman]

If all the problem was that the tyre valve was leaking in the pressure vessel all it needed was a new 20pence valve from the local
car spares place. Sorted.

Not if it was leaking water

 

[PCatterall]

Many thanks guys for the advice.
My little brain has been working overnight on this as well!!
The existing vessel is mounted horizontally in the boiler, I though it would be good to mount my new vessel horizontally as well, partly for space and also so I could easily check and top up the pressure if required.

BUT ( foolish boy) I realise that the existing( horizontal) vessel is filled not from the end but from the highest point on the side.
By mounting mine horizontally I believe the 'water end' is not filling with water ( as you suggest)but is getting air trapped. As the water heats the air is trapped and pressurised causing the burp or bang that I heard.
That's my theory and we will remount the vessel today and try again.
I will report back!! hopefully a basic mistake.
many thanks.

PS yes, sorry it was leaking water.

 

[matt1e]

Your theory is wrong mate
Much more likely there is a restriction/ blockage in the pipe or you don't have the correct precharge in it.
It would have been easier just to have plumbed it into the boiler return as per steels post above
how have you routed the flexi out of the boiler, are you sure this isn't kinked/trapped?

Matt

 

[PCatterall]

Thanks again Matt,
We refitted the unit in the vertical plane and ( you were quite right Matt) had a similar result!! Fired up for about a minute then pressure soared, a couple of bangs and the gas cut off, this happened several time.
Pressure vessel pressure checked, no kinks in pipes etc.
Scratched head ( a lot ) our set up seemed to just replicate the original one so we couldn't see why there was a problem.
Persevered with starting the system just using the hot water side but switching off as soon as the pressure needle started to flicker. We then allowed the system to run on and cool down before starting it up again.
Eventually it settled down and it is now working fine and has been tested for several hours.
Possibly there was some sort of air lock in the system, the shutting down seemed to be associated with possible overheating.
Any way, problem solved, mainly thanks to you guys.