Another negative head shower problem!

[adamwest]

Lucky me, half way through an MFI installation of a negative head shower and they go bust. The originally plumber was having troubles, but now no-one seems to know what to do. Can anyone help?

- CWS level with the pump, in the loft
- HWS about 2 metre below the pump, in spare bedroom
- Shower about level with HWS, head usually about 1 metre above HWS, 1 metre below CWS/pump
- After problems with air, plumber fitted air valves (?) before and after the pump on both hot and cold. Worked for a week.
- Now, no hot water is pumped. Pump (salamander 1.5bar) selects negative head mode, inflow pipes run hot, but outflow pipes stay cold.
- Salamander say air valves un-necessary, and that the pump should be below the CWS...

But surely that's what a negative head pump is for? I don't want to put the pump in the spare room as it will wake the baby.

Any ideas before I spend even more on this wild goose chase? Hope this description is logical/makes sense?

 

[Richard C]

- Salamander say air valves un-necessary, and that the pump should be below the CWS...

But surely that's what a negative head pump is for? I don't want to put the pump in the spare room as it will wake the baby.

Any ideas before I spend even more on this wild goose chase? Hope this description is logical/makes sense?

Salamander is correct I’m afraid; it seems to be a common misconception that a negative head pump can be mounted above the CWS tank, not so. Negative head means the shower head can be located above the CWS tank (as in loft conversion), the pump itself must still have a positive head on the CWS tank to operate i.e. be mounted below the tank. The minimum positive head specified on the CWS tank varies depending on make 200mm for Stuart Turner but Salamander say 600mm.

Have a read here it may help you understand a little better;
http://www.salamanderpumps.co.uk/Download/instructions.pdf
http://www.stuart-turner.co.uk/PDF/18059-20-11.pdf

 

[adamwest]

Thanks Richard - that makes sense and is useful. Does the lack of CW head explain the inability to pump HW? If so, before doing major surgery might it be worth raising the CWS a few inches (can't do more).

 

[Richard C]

Does the lack of CW head explain the inability to pump HW? If so, before doing major surgery might it be worth raising the CWS a few inches (can't do more).

I would say almost certainly yes the cold water has got the easy route so wins every time. I take what you’ve already said about not wanting the pump in the spare room & they are never as quiet as you imagined but by far the best place to install the pump is around the bottom of the H/W cylinder as it gives a really good positive head for the pump to feed from.

If you’re going to stick with an elevated pump & raise the CWS tank, I would try & ensure you can get around 1m rather than the minimum 600mm if you can otherwise you may still be dissapointed. Don’t forget the anti-gravity loop & if you’ve got up & over pipe work to the shower head, you will need air vents on the top of the loops; the shower will work initially but will eventually grind to a halt as air builds in the top of the loops to eventually form air locks.

Funny stuff water!

 

[adamwest]

Gotchya, thanks Richard. I think I can raise my HWS by about two feet so I might just be alright. My current install has vents in what looks like might be an anti-gravity loop but Salamander said take them out - it says never use vents in the installation guide - which seems odd if the anti gravity loop needs them and if you'd always need the loop if the pump is above the shower. You're right - water is not a simple thing!

 

[Richard C]

I think I can raise my HWS by about two feet so I might just be alright.

How is that going to help or do you mean the CWS tank?

My current install has vents in what looks like might be an anti-gravity loop but Salamander said take them out

If you’re saying there is a vent in the h/w cylinder anti gravity loop I don’t understand why it’s been put there

it says never use vents in the installation guide - which seems odd if the anti gravity loop needs them and if you'd always need the loop if the pump is above the shower.

However, I’m a little confused that you say Salamander have said that you don’t need vents in up & over loops down to the shower valve; where exactly in the installation guide does it say you should not have vents? I believe it states the opposite!

 

[adamwest]

Richard - you're a smart guy! You even spot my mistakes as well as my plumbers...

Yes I meant I could raise the CWS...which to my eye isn't really the problem but the original plumber said it might help to get more head on the CW (which you seem to agree with?)

The vents are before and after the pump on HW and CW - actually I don't think we've got an AGL at all as that would normally be between the storage and the pump yes?

Sorry if I'm not clear - Salamander say never fit vents in the system with the pump - unless I've missed a reference to fitting them in an AGL?

I now have a plumber who is recommending moving to an unvented system and disposing of the pump altogether! More googling for me!

Thanks for all the advice Richard!

 

[Richard C]

Richard - you're a smart guy! You even spot my mistakes as well as my plumbers... Yes I meant I could raise the CWS...which to my eye isn't really the problem but the original plumber said it might help to get more head on the CW (which you seem to agree with?)

The vents are before and after the pump on HW and CW - actually I don't think we've got an AGL at all as that would normally be between the storage and the pump yes?

You should not have vents before the pump; the h/c water pipe work should be installed such there are no inverted loops before the pump. An anti gravity loop should be formed between the HWS cylinder & the pump.

Sorry if I'm not clear - Salamander say never fit vents in the system with the pump - unless I've missed a reference to fitting them in an AGL?

See the Salamander installation guide;
http://www.salamanderpumps.co.uk/Download/instructions.pdf
Yours should look somewhat similar to figure 13, including the vents at the top of the up & over pipe loops to the shower mixer; I think there is confusion somewhere!

I now have a plumber who is recommending moving to an unvented system and disposing of the pump altogether! More googling for me!

What’s he proposing? It seems a rather radical & expensive approach considering you’ve already got the pump & most of the other components in place; it seems to be just the pipe runs & installation that needs sorting out! I don’t think a sealed, presurised system, even with a hws storage cylinder will match the performance of a decent sized, dedicated shower pump.