External Vessel with Combi

[jaydebruyne]

I'm fitting an external vessel on a combi system whose vessel is defective.

Leaving in the old vessel inside the combi as I'd have to take the boiler off the wall to replace it.

The external vessel just goes on the return pipe as close as poss to the boiler, doesn't it?

Cheers
Jay

 

[solutions]

Yes.
If you can get on to same connector on the hydro block on the boiler then perfect. Otherwise on the return as you suggested as close to the booler as possible so it is exposed to as slow and low temperature changes as possible which will prolong its life.

 

[jaydebruyne]

Yes.
If you can get on to same connector on the hydro block on the boiler then perfect. Otherwise on the return as you suggested as close to the booler as possible so it is exposed to as slow and low temperature changes as possible which will prolong its life.

Cheers mate...

 

[Ch4 plumbing]

Just cut it into the return pipe near the boiler mate, easy as that.

 

[lame plumber]

or to make it easy, drop the filling valve off, add a T and pop the expn vessl and filling valve back on, easy peasy ( on the return side mind )

 

[solutions]

Strictly speaking there should not be a valve between the heat source and the vessel but obviously you cant take of a boiler service valve and a boiler is not going to fire for long if at all if the service valves are closed so it is common to do as has been suggested. Try and fit the vessel with copper pipe not a flexi and with the opening down and the schraeder valve on top. If you have to loop the pipework up put a drain off on the low point on the pipe to the vessel so it can be drained if it has to be changed or you can open the drain off on to a hose to check the precharge of the air bladder. Worthwhile if you may service the system again in the future.

 

[jaydebruyne]

Just cut it into the return pipe near the boiler mate, easy as that.

Yeah I was planning to.. I'll probably get to plumb centre and find out they've ordered the internal one and I'll have to take the boiler off the wall ...

 

[Ch4 plumbing]

Yeah I was planning to.. I'll probably get to plumb centre and find out they've ordered the internal one and I'll have to take the boiler off the wall ...

Always makes for a good start to the day!

 

[jaydebruyne]

Strictly speaking there should not be a valve between the heat source and the vessel but obviously you cant take of a boiler service valve and a boiler is not going to fire for long if at all if the service valves are closed so it is common to do as has been suggested. Try and fit the vessel with copper pipe not a flexi and with the opening down and the schraeder valve on top. If you have to loop the pipework up put a drain off on the low point on the pipe to the vessel so it can be drained if it has to be changed or you can open the drain off on to a hose to check the precharge of the air bladder. Worthwhile if you may service the system again in the future.

I was just going to tee into the return underneath the boiler (its up high in a tall kitchen cupboard with a lot of space) and fit it in the upright position with the Schrader at the top.

 

[plumben]

Don't forget to make sure its sized correctly for the system

 

[jaydebruyne]

Don't forget to make sure its sized correctly for the system

How do I go about double checking???

 

[GrahamM]

How do I go about double checking???

What size is the one in boiler? MI's usually tell you. Generally an 8L vessel will suffice for average house.

 

[jaydebruyne]

What size is the one in boiler? MI's usually tell you. Generally an 8L vessel will suffice for average house.

Yeah I'm picking up an 8ltr vessel so all good then cheers Graham

 

[plumben]

How do I go about double checking???

Theres apps like Mr Combi https://itunes.apple.com/gb/app/expansion-vessel-calculator/id646104473?mt=8

Or as said check what size the boilers got fitted although depending on the system some boiler expansion vessels can Be to small for the job but that's rare

 

[Best]

I usually use a 12litre vessel minimum for fairly small systems - semi detached 3 bed home about 8 or 9 rads, for example. Any house slightly bigger I use 18litre. Obviously much bigger houses I need to go larger and you have got to think of underfloor heating pipes as well as rads & pipes & boiler (as oil boilers can have a fair bit of water). You can't go wrong slightly oversizing & probably is better that the vessels membrane is having to stretch less & last longer. They are cheap anyhow.