Very Loud hissing noise

Ah, I see your problem, you need to connect the taps to the water supply instead of the gas. Easy mistake to make.

Apologies. Should have clarified that they are connected to the water but the water comes out of the taps with this loud noise

LOL

1. add a restriction further back than the taps. A service valve partway closed will do it. This divides and moves the hissing, moves it to behind obstacles instead of by your ears.
2. Lag the pipes, this absorbs sound

NT

wrote

Could simply be that the plumber has opened the water stop c*ck further after doing the job than it was when he shut off to make the changes IYSWIM. Does water come out of the mains fed cold taps faster than before he started? Closing down the stop c*ck a bit may cure it, but may also affect combi performance - don't know about combis, don't have one!

Phil

Yeahrightbolloxmyarse.

A. 1. Find mains stopcock.

1. Turn c*ck slowly clockwise until an acceptable balance is reached between the amount of water coming out of the tap and the noise level. More water = more noise. Less water = less noise.

B Get plumber to fit flow restrictor on pipe to affected taps.

Owain

Let the air get out.

ISTR someone discovering that one of their washing machine inlet pipes was fed from the gas supply in a new house...