Salamander pump installed but reduced flow when mixing

Trebuchet95

Trebuchet95

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I've had a Salamander negative head pump installed in the airing cupboard, just above the HWC. The HWC has has an Essex flange with the required anti-gravity loop installed and the cold water tank is about a metre above the pump in the loft. The outputs from the pump go back up into the loft and there is a straight run of about 3m to the en-suite bathroom where it drops down into a Swirl mixer shower.

The issue I'm facing is I get very good flow when it's fully hot or fully cold on the shower mixer, but when trying to get a reasonable temp, the flow starts weakening & getting cooler and I gradually have to move the mixer towards towards the hot till it become warm enough. It'll stay at the correct temp, but the flow is now noticeably weaker.

Having looked around on the internet, I did think it was an issue with the mixer which I taken apart from check the cartridge and it seems to be ok. Strangely, when I take off the shower head from the hose, I get fantastic flow at the right temp coming out of the hose, even when it's up on the shower rail and not on the floor. It's only when I've got the shower head on that the flow is weak. I've tried a couple of other shower heads which I hoped would solve the issue, but haven't found one to completely solve the issue.

I have thought it's perhaps because it's a long run from the pump output to the shower mixer and I don't have an automatic air vent installed at the highest point, but not positive this will solve my issue.
 
is it a thermostatic mixer? which side is the hot pipe attached to?

where does the cold water come from?
 
JohnD said:
is it a thermostatic mixer? which side is the hot pipe attached to?
where does the cold water come from?
Click to expand...

It's not a thermostatic mixer, just a manual mixer which was originally in the en-suite when we bought the place this year.
I should have specified, the Salamander pump in a twin impeller and is used to supply both the cold and hot to this one shower only.
 
and where does the cold water come from?

the loft tank?

or the watermain?
 
The cold water is supplied by the cold water tank which is about a metre above the pump in the loft. It is only 50 gallon so we have had to have a water starvation unit installed, but the water in the tank has never fallen enough to cut out the pump while having a shower.
 
What pump is it? Usually the pumps have the pressure shared between the sides on a twin, so if the output increases then the available pressure can drop. The lower the total output of the pump the more noticeable the pressure drop will be.
 
Madrab said:
What pump is it? Usually the pumps have the pressure shared between the sides on a twin, so if the output increases then the available pressure can drop. The lower the total output of the pump the more noticeable the pressure drop will be.
Click to expand...

It's a Salamander RP50TU. That doesn't really explain why the flow is fantastic coming out the shower hose with no shower head.
 
Because the shower head is a restriction and will always impede the output of the pump, that's just the way it is.

You've really answered your own question, obviously the shower head is the restricting factor. All that can be done is obtain the highest flowing shower head possible and whatever the output is, is what it is.

Flow and pressure are 2 different things ..... the RP50 drops to 1.2Bar @ 8L/Min output and 1bar @ 16L/Min.
 
I see. Any suggestions on high flow shower heads? All the ones on Amazon seem to be "eco" and unlikely to make things better.
 
Going off on a tangent, the long run for the hot & cold outputs from the pump going across my loft to my shower is in 15mm. It disappears into the bathroom wall to the enclosed mixer valve, but would replacing the 15mm pipe with 22mm reduce the head loss even if it has to go down to 15mm for the mixer?
I'm planning to replace the output pipes from the pump to the shower as the plumber (this was after 3 visits to fix issues!) has put in so many bends to make it look "neat" I suspect I'm losing a lot of head through that. Also it's all in 15mm and he's also not put the automatic air vents in the correct place (after the output from the pumps, but the pipes continue up into the loft after the vents so obviously not at the highest point).
Wish I had the chance to read the Salamander manual fully before the plumber installed the pump so I could've told him all the things he was doing wrong.
 
Keithmac said:
Sounds like your new pump is just undersized, underpowered?.
Click to expand...
I have thought about buying a 2nd hand RP75TU from Ebay (not willing to pay £350+ for another pump), but I don't like the plumbing I've been left with.
Funnily enough, when the plumber originally installed the pump in the loft, the pipes to the shower were nice and efficient and the flow was good. The only problem was he neglected the required 60cm below the cold water storage so Salamander invalidated the warranty when I complained the pump won't stop after using the shower. Had to have the pump moved into the airing cupboard (and have water starvation unit installed) to restore the warranty.
 
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