Pump for Gravity-fed HW - for bath/show mixer only

[wjotner]

Please help, total novice at plumbing:
The cold feed in the bathroom is direct mains. And very powerful.
The hot water in gravity fed. the pressure is rubbish. Its only 0.3 head at the bath taps.

I need to fit a reasonably powerful thermo mixer shower.

So i realise i need a single impellor pump for HW to match high powered cold feed.

But where is best place for the pump? I don't want to pump the hot water into the kitchen or bathroom sink. I only want to pump the HW for the bath/shower mixer. So don't want to fit pump in airing cupboard as it#ll effect HW supplies to all outlets.

Would like to fit near bath taps, even under them. Can the pump be fitted lower than the taps? Will i need Negative pump? Aren't they more expensive than normal pumps? Any advice much appreciated, as really can't afford expensive plumbing labour. Would like to do myself if installation is relatively simple.

Thanks

 

[twgas]

You would need a twin impellor pump and the cold would need to be rerouted, with its own dedicated supply, from the cold tank in loft, through pump to shower. The hot would, ideally, have a seperate tapping from the cylinder, again, through the pump and on to the shower.

 

[wjotner]

Hi Mick

Thanks for the reply. But not possible. My tank is not in loft. I live in a top floor flat in a block. My tank is in airing cupboard. And its not big enough to supply cold and hot water for a shower of any power. It would drain in a couple of minutes.

Not to mention the expense and hassle of routing piping from my airing cupboard, through the kitchen, and then through kitchen wall into the bathroom.

I need simplest, cheapest option. Any ideas?

 

[Whitespirit66]

You can't pump from your hot cylinder as it stands, because as well as drawing water from it, you will also pull air down the vent pipe (cavitation). This will affect the pump.

You need to either;

A) Fit a Surrey or Essex flange to the HW cylinder and pump directly from this new outlet to the bath/ shower. This will obviouly need a new dedicated HW supply pipe from the flange to the pump then onto the bath/shower.

B) Fit a Surrey or Essex flange to the HW cylinder, and pump from this to the whole flat through the existing HW pipe that leads from the cylinder at present.

 

[rojaca]

I'm imagining that you've got whats called a combination or "fortec" cylinder around here. If this is the case I doubt you will be able to pump off this. I think you will find that the header would be depleted to quickly by the pump.

 

[twgas]

electric shower springs to mind - I know, you can't get a new cable through for that either.
Or stick to baths.

 

[ChrisR]

I've seen it done by putting a pressure reducing valve on the cold under the bath, set very low, and a small pump in the hot, and two float valves in the CW cistern to get it to fill faster. But the guy who did it was a plumber and he lived there, and he was constantly fiddling with it!

 

[wjotner]

Hmmm. Much to ponder. Thanks for your advice. I think the mostly likely solution is simply fitting the flange on the cylinder vent and pumping hot water to all outlets. Not ideal, but might have to do.

Electric shower will be absolute last resort. I can't stand them. But better than bath all the time i suppose.

Cheers

 

[ChrisR]

simply fitting the flange on the cylinder vent

Eh?

A Flange on the cylinder, not the vent, would be your best bet but it'll still possibly suck air down the vent pipe. An Essex flange is normally easy and best but may be hard to fit on your tank.
But if you pump out at say 20 litres/minute and the mains is filling the cistern at 10 and the cistern's a Fortic it'll run dry pdq.