Pressursied water system

[cpizzey]

New house with a pressurised water system (new to me).

All OK until builder replaced a radiator.

Central heating still OK, hot water taps still OK but shower now either cold or tepid even on full heat.

Should I open the line between the red vessel & the white precharge vessel? Indicator on red cylinder presently reads approx 0.8 bar.

Thanks,

 

[Spike295]

Its probably just coincidence that the shower is not working properly around the time a rad has been installed but the most likely cause is that cold mains is passing thru the shower & over powering the hot. To cure this you need to fit non return valves on the hot & cold supplies to the shower.

 

[Alanka]

Re: Pressurised water system

If the system is 'pressurised' it would normally mean that the hot and the cold water are both at the same (or nearly so) high 'mains' pressure. So the cold water would not be overpowering the hot supply within the shower, as they are both at similar (high) pressures.

Fitting non-return valves would not help even if the cold supply was at a much higher pressure than the hot supply -- you would still only get cold water out of the shower because the hot water nrv would be clamped shut by the cold back-pressure!

The problem may be crud in the shower mixer or handset, or an airlock in the hot supply to the shower.

 

[Spike295]

Yes the cold will over power the hot on a pressurised system, although the hot & cold are high pressure they are not equal pressure! The cold will be higher but not to the extent of jamming a non return valve shut!

The mind boggles sometimes with peoples way of thinking!!!!

 

[Alanka]

Not so. The cold water pressure would have to be substantially higher to overpower the hot flow -- I mean like mains cold water versus tank-in-the-loft-fed hot water! With most pressurised systems the pressures are fairly close (though not exactly the same of course.)

Think about it: if the cold water pressure is high enough to cause reverse flow back up the hot water supply pipe, the hot water nrv WILL shut off. That's why it's called a non-return valve, and that's how it works.

Non-return valves are not a way to cure unequal pressure problems. They simply prevent water flowing in the reverse direction (which is usually flouts water regs). They do not help the water to flow in the correct direction.

Think clearly and logically, rather than boggle!