15mm or 22mm HW pipes runnign from combi?

[macadonald]

Hi guys,

Have another post running, which started with a dif question, so worried it will get missed, hence the new topic.

Just had a combi installed in the loft and it has 22mm HW and CW pipes running from it. The pipes remain 22mm to the bath and basin in the bathroom, but appear to be 15mm in the kitchen sink downstairs. Someone else in the forum mentioned that the HW pipes should be 15mm throughout and indicated the plumber had not done it correctly with 22mm pipes.

I will be installing a thermostatic shower diverter in the bathroom as well. Not sure if it's at all related to pipe diameter, but I am a little disappointed in the bathroom when I have the hot running and turn on the cold. The hot turns to a trickle. I know this can be expected with combi, but it concerns me that my new mixer taps might not work expected.

Any thoughts?

 

[Whitespirit66]

22mm is fine for hot and cold pipework. Sounds like you need to do the obvious first, and check that the main outside stop tap is fully open, and any other internal stop taps or isolation valves are fully open.

 

[macadonald]

Thanks for the response, but to be honest I am getting very confused. I have some people responding to my other post saying that HW must always by 15mm, and other saying either will do.

My boiler is a vailant 28kw pro.

Sorry, just don't want to approach my plumber if what he has done is fine.

 

[Andygasman2010]

I've not read your other post so sorry if i'm repeating anything. Ideally the hot and cold pipework should be all the same size preferably in 15mm. If you use 22mm the flow rate is too great for the combi and you get cooler water than you should. (You will have to restrict the flow at the tap)

I supose this could be made worse by having a mix of the two sizes and especially if it goes all the way to your loft then back down.

Also, you end up with quite a delay before getting hot water as there is more volume within the pipe.

Remember, the boiler has 15mm hot and cold connections for a reason.

 

[Morris40]

Andygasman is quite correct should be 15mm pipe from combi on HW not 22mm