noisey when hot water comes out of taps

[goateater]

hi
last year i replaced a lot of 15mm hot water pipes with 22mm pipes
now when i open the hot taps down stairs it sounds as if air is trying to get out
if we use the downstairs shower for a few weeks the water coming out seems to reduce, so i have to turn the shower/bath mixer tap on to bath and it sounds as some air is coming out, when i switch shower/bath mixer back to shower water is normal again
i have only changed the pipe work after the leg that feeds my downstairs pipework
all stopcocks are open fully
i can't see any leaks, there are no doglegs in new pipework, just can't see what probelm could be

 

[Cpplumber]

Have you modified anything near the cylinder? I'm assuming you have an indirect vented cylinder?

The Hot water pipe leaving the top of your cylinder (the one bang in the middle, right at the top) should be angled slightly upwards towards the vent. The vent goes up to the cold tank and hangs over it. Any air in the hot water then finds its way out the vent on its own. What can happen if this isn't the case, is, aerated water in the cylinder releases air when it's heated. The air bubbles then get trapped in this piece of pipework at the top and cause problems with air and supply. If the section between the cylinder and vent pipe runs down hill then the bubbles form above the cylinder. You can often hear this as a churning bubbling sound at the cylinder when a tap is running.

This is a stab in the dark but might be worth a minute of your time to check.

Cheers
Carl

Hopefully this makes sense?

 

[goateater]

carl

thanks
air vent from cylinder is ok,
so i'll check to see if i can hear bubbling at cylinder with tap running

don't know why i would have aerated water in cylinder.
gives me something to think on

 

[twgas]

if we use the downstairs shower for a few weeks the water coming out seems to reduce

that is some shower you're having surprised it's not cold after that.