Lowering water flow at mains, lowers pressure?

[sharpears11]

Apologies for asking a question which has probably been asked a hundred times (Google search didn't filter for me what I was looking for), and for not having basic physics knowledge, but...

If I lower the flow at the mains outside (Thames water installed stop cock) outside my property boundary for my house, will that lower the water pressure going around my system?

Some context:
I have a unvented system, with some type of 'megaflow' copy connected to a expansion vessel (no gauge so cannot read pressure), using a system boiler, of which I know is a Valiant.

During the times set for the hot water to heat, and for the first time of use of the hot water after that cycle I hear a bang coming from the Expansion vessel and its pipe. I dont know 100% for sure if its coming from the vessel but its around that area.

I'm not sure if it is of importance but I'll mention that the boiler is on the ground floor, and the unvented cylinder and the expansion vessel is on the first floor.

Thanks for taking the time to read and respond.

 

[picasso]

No closing the stopcock a bit makes no difference to the pressure of your system, all it does is reduce the flow rate, have your unvented cylinder serviced/repaired rather than trying to mask the symptoms.

 

[Madrab]

Are you talking about the central heating system is un-vented or just the hot water system? Is the expansion vessel you're talking about on the cold inlet into the cylinder? If so, the unvented hot water system should have a pressure reducing/combo valve on the cold inlet prior to that expansion vessel. It may be that valve or the pressure relief valve that's causing it if the pressure's getting too high.

If there are any issues with your unvented hot water circuit then it's really important that a qualified G3/UVHW cert holder does the work and ASAP.

 

[sharpears11]

@Picasso: Thank you, the system is 3 months old from new. I'm waiting for a water pressure gauge to arrive so I can check my water pressure, and will need a plumber to check the expansion vessel by the sounds of it.

@Madrab: Thank you also, Yes we are talking about the hot water system (the boiler for the central heating also heats up the water in the cylinder indirectly). From what I can see, the expansion vessel is off the pipeline supplying cold water to the water cylinder, and yes there is also a PRV on the very pipeline into the water cylinder (the PRV has a seperate out pipe to a waste pipe).

Thank you both, while I'm not a qualified plumber/engineer, it does sound like the root cause of my problems is cold water pressure related seeing that I (think) the noise is coming from the expansion vessel+connecting pipes, going into the water cylinder.
The thing that baffles me is why am I hearing the noise when I open the hot water, and not the cold water?

 

[Madrab]

When you open the hot water tap the cylinder draws cold in from the mains, through the PRV, past the EV, that's how it gives you high pressure hot water. If the PRV combi is clicking then it will need checked.

All that being said, I would suggest it's time to get the guys back in who installed it, if it's only 3 months old!! Get them to check their installation and that should encompass all the safety devices including the EV.