Combi modulating water flow?

[David]

WB combi and potential slow flow - still not got round to comprehensive diagnostics.

I've just (duh!) noticed that if the upstairs shower is turned to full cold then the water fairly blasts out - so there is pressure and flow at least in some of the cold side.

Boiler is a WB Greenstar CDi Classic 38CDi. Manual says 19.i lpm 30C temperature rise, 14 lpm 40C temperature rise. It was sized to be able to run two thermostatic mixer showers at the same time. Well over specified to heat a 3 bedroom semi.

I'm still not clear if it throttles the water flow to enable it to meet the chosen temperature setting.

If it does, I assume that if I turn the boiler off and just run cold through it this should show if there is something in the pipework on the hot side which is restricting the flow?

Still puzzled, because a smaller version with the same shower mixer in a previous house managed a much higher flow rate when filling the bath.

As mentioned a while back, I don't currently have an unrestricted hot take off - everything goes through a mixer tap or a thermostatic shower.

One day I will find time to do some proper measurements.

Cheers

Dave R

[Bob Minchin]

If it is anything like my WB (non combi) the documentation is all there on WB website including the service manual, all parts listed etc so you should be able to see if there is a modulating valve in the water flow from the comfort of your armchair.

[David]

Looking more and more like some kind of restriction between the boiler and the thermostatic shower mixer.

I think I'm just looking for excuses to avoid taking the bath panel of (if it will come off).

[dennis]

You haven't got one of those shower savers fitted on the flexible hose have you? They are designed to restrict the flow and are just a disk with a very small hole.

[David]

Not as far as I am aware - restriction is also on filler for the bath as this is a combined thermostatic shower mixer/bath tap mixer.

Wondering if the wrong type of isolation valve has been used (i.e. not full bore).

Cheers

Dave R

[Tim+]

Distinctly possible. Can you post a link to a picture?

Restricted bore ones look "waisted" whereas full bore ones are fatter in the middle, though not by as much as you might imagine.

Narrow bore:

$p$&layer=0&size=281,281&layer=1&size=281,281&src=ae235/65251_P

Full bore:

$p$

Tim

[John Rumm]

However at (high) combi pressures you are unlikely to notice the difference - its more of an issue on gravity fed systems.

[Capitol]

Is the shower hose kinked? I fitted a new 11mm id one last week and its rubber pipe was almost completely blocked when removed from the packaging. Never seen that before.

[David]

I suspect one issue is that the pressure is only medium at best. But then again the pressure limiting valve for the water softener is showing 3 bar.

Another great mystery of the sea where I can't get it to the top of my priority list. Only high enough up to grumble occasionally. :-(

Cheers

Dave R