Water connection upgraded

[liquidfusionv]

I'm have no experience in plumbing so please don't bite

My builder suggested I upgrade my existing 15mm water connection to 25mm which has been done and fitted, however looking at the internal stopcock it receives at 25mm MDPE connection however drops back down to 15mm again and goes to wherever I'm not sure.

Can someone tell me why a 25mm x 15mm stopcock was used, doesn't this defy the purpose of the upgrade as my previous water connection was already 15mm.

My boiler is vaillant 837

 

[Tibbot]

You would generally convert to 22mm after the 25mm pipe. However upgrading your supply is never a bad thing and means you have spare capacity should you ever re plumb the property, eg for a mains cylinder. 15mm is OK for your combi.

 

[liquidfusionv]

You would generally convert to 22mm after the 25mm pipe. However upgrading your supply is never a bad thing and means you have spare capacity should you ever re plumb the property, eg for a mains cylinder. 15mm is OK for your combi.

Thanks, is there any reason why you could think of for them to drop from 25mm to 15mm, instead of what you said from 25mm to 22mm?

It seems like such a big drop, and can't think of a reason why

 

[Tibbot]

Your combi boiler would usually require a 15mm supply because of limitations of it's hot water production (about 15l/m for the 837). Unless you had major cold draw off required before the combi eg external water features, sprinklers etc. that should be all you need. Even storage combi's such as the old Worcester Heatslave oil boilers that featured a 22mm hot outlet only required a 15mm inlet.

For a combi good pressure will be more important than extra incoming flow rate of 22mm.