Low water flow

[Mal87]

Just had A Vaillant VIH GB 210 S unvented hot water storage cylinder installed to give us mains pressure hot water. When turning hot water on followed by cold water (on full) hot water totally dries up. Had the water board out who said I have 18 litres per minute coming out of tap at 3 bar. The instructions for cylinder state that there should be beteen 20 to 25 litres per minute with minimum of one bar. My in let pipe from the water board main in street is either 12.5mm or 15mm. If I lay a new pipe and increase the diameter to 25mm will I achieve a flow rate of over 20 litres per minute that will supply enough water to supply cold and hot tap simultaiously. Also if I installed the larger 25mm incoming pipe should both the cold and the hot take their supplies from the 25mm pipe?

 

[Agile]

The crux of the matter is that you need a good dynamic pressure.

Your cylinder needs 20 li/m whilst leaving 1 Bar pressure in the supply.

Your installer seems to me to have been seriously neligent not to test the supply and advise you of the limitations.

If I knew what I know and was in your situation I would be expecting him to upgrade the supply himself!

There are too many unprofessional people doing substandard work like this! Is he a member of the Institute and is he Certified under G3? If not certified then he should not have fitted the cylinder!

How would you rate the installer???

Tony

 

[Mal87]

Thanks for reply. Think my plumber/installer has realised this and we are now working to resolve. But would fitting a 25mm pipe cure the problem?

 

[chrishutt]

Had the water board out who said I have 18 litres per minute coming out of tap at 3 bar.

That doesn't sound right. I expect the pressure is static pressure, whereas what you need to look at, as Agile pointed out, is the dynamic pressure for a given flow rate (e.g. 18 l/min). Your plumber ought to have some grasp of pressures and flow rates. Presumably he doesn't have the "unvented ticket" and shouldn't be installing unvented cylinders anyway.

 

[Mal87]

How is dynamic pressure measured? The water board connected a pressure gauge to CW tap, I take it this was static pressure? The flow rate was measured using a Weir Gauge. But how do measure the prssure with the tap on? As you may gather I am not a plumber!