HW under bath pump

[DarkKnight]

Hi,

My electrician has gone AWOL, so I'm going to have to do the work myself and then retrospectivly get him to approve it.

The how water pressure upstairs in my rental home is very week (gravity fed from loft). It has a mixer tap with a built in shower hose. I wanted to beef up the pressure by fitting a a pump to this tap feed. My specific goal is to increase the Hot water shower pressure.

I think my water system is a gravity fed one, hence the poor pressure.

The pipe work for the water to pump is straightforward enough (T off Hot water to Pumps inlet and outlet) however, I need some advice on the electrical work. I haven't purcahse the pump yet, but I expect it to be a regular 13 amp fused plug.

I was planning to drop the cable from the loft to provide the power supply to this pump. I need advice on the following : - Should the Pump be wired directly to the electrical spur I'm dropping from the loft ? (i.e. remove plug ?) and be encased in a water proof box ? - What IP rating junction box should I be using if it's under the bath ? (Whether it's a junction box for above bullet point, or an electrical socket) - Are there any guidelines about trunking or where the electrical cable should be 'tacked' ? - I plan to have an isolation swtich outside the bathroom, above the entrance door. Would this be compiant with electrical guidelines ? Or should I use a pulley switch from within the bathroom ?

The guys I have doing the pipe work are working on it today, so a prompt response would be much appreciated.

Rest assured, I plan to have the electrical work fully approved before I switch it on.

Thanks

[TheScullster]

"DarkKnight" wrote

Decline to comment on the electrical side - others will be along. On the plumbing, you need to give some thought to where the hot supply is taken from. Most shower pumps require (or at least prefer for longevity) to have a separate take off from the hw cylinder. Either that or the take off needs to be in a specific place on the main hw supply from the cylinder - recommend you look at shower and shower pump sites to check this. Also many showers will prefer similar feed pressures on both hot and cold. So you *may* need a twin impeller pump with gravity cold feed to one side and gravity hot to the other. I'm sure others will be along to expand on this, provide links or completely disagree

Phil

[jgharston]

You don't get weak pressure "because" it's a gravity-fed system. You get weak pressure because there is insufficient pressure, either due to a gravity feed system having insufficient head (ie, the tank is not high up enough) or because a pumped system is not pumped to a high enough pressure.

You can get perfectly good pressure from a gravity system, though when feeding a shower, the cold should be fed from the same tank as the hot, to ensure the pressure matches.

If there is room, an adequate gravity head can be made by raising the hot water system's feeder tank. If it's on the floor of the loft, you'll only have about two feet of head to the shower. Raising it five to six feet off the loft floor is adequate.

-- JGH

[DarkKnight]

Thanks for the plumbing advice.

I would imagine raising the gravity head would be more 'ball ache', simply because of the amount of re-plumbing that would be expected.

The HW is turned off at the moment, but from what I can recall, standard pressure on the taps was adequate. But going up the mixer tap to a built in shower hose, is where the HW pressure supply is p*ss poor. (quite literally).

Hence why I'm trying to concentrate solely on the HW bath tap mixer.

I see your point about taping from from the HW storage, but I don't want to fix what's not broken.. i.e. If other taps are fine, then I would prefer to leave the pressure as is.

Are there any sparky's out there who could advise on the electrical work ?

Thanks

[Roger Mills]

I'm not a sparky - but I do all my own electrical work - and plumbing - and installed a shower pump under the bath many years ago. Unless your plumbing is faulty - and you'll have lots of other problems if it is - the under bath space should be completely dry - so you don't need anything fancy in the way of high IP numbers for electrical connections. The pump should have a built-in flow switch, which switches on the motor as soon as water starts to flow by gravity - so all you need is a live feed. My bathroom backs onto a bedroom with a fitted wardrobe. Inside the wardrobe - and so completely outside the bathroom - I put a fused switched spur box, with a neon indicator - with the output from that going down through the stud wall and emerging under the bath. Simple!

As others have said, if you're feeding a shower mixer, you really need a twin impellor pump with hot *and* cold gravity feeds at the same pressure as each other. So you need a cold feed from the header tank to the pump in addition to tapping into the bath's hot feed. If you take things *really* seriously, the cold feed needs to be *below* the cold take-off to the hot cylinder. That way, in the event that you empty the cold tank, the hot stops before the cold so the shower runs cold rather than scalding you.

[TheScullster]

"DarkKnight" wrote

Problems with using a existing supply for the feed to the pump won't necessarily be obvious simply by observing tap behaviour. When you run a shower pump you evacuate the pipe upstream of the pump. If the feed is not adequate, or the hot take off from the cylinder is taken in a way that will tend to include entrained air, then the pump will cavitate, resulting in noise, poor performance and premature failure. Check out your piping against recommendations made by the pump/shower people or you may live to regret it. In this instance, the quickest way may well not be the best in the long term.

Phil

[DarkKnight]

Hi,

Looks like a change in plan. From everyone I've spken to so far, I should be tapping from the storage tanks / cylinder.

Problem is, how is this done if the cold water tank is in the loft and th cylinder is downstairs ? ((Yet the swer is upstairs!) Is there a cold water feed comign / in / out of the cylinder which could be connected to a double inlet pump ?

I assume all pumps are designed for connecte 'at source' in this way (rather than conecting to taps directly) ?

Thanks again

[TheScullster]

"DarkKnight" wrote

The important issues on the hot side are to avoid entrained air and to have an adequate (probably 22mm) supply - check the pump requirement. If you cannot satisfy this condition with a take off locally, then the optimum solution is an "essex flange" into the side of the cylinder. This of course means also bringing a dedicated cold feed from the loft storage tank down to the pump and then taking feeds back up to the shower. The advantages of doing all this are: More accessible pump (probably) Reduced noise from pump as it is likely to be on a more solid base at ground floor level rather than on the first floor where sound will be broadcast around the house.

Phil

[Rod]

We have something of the same situation (in principle). Our problem was poor shower performance. So we fitted a power shower (nothing fancy).

Our cold tank has two 22mm outlet pipes - one to HW cylinder, the other feeds (mainly) CW in bathroom. Being wimpy, our power shower is happy being connected to the H & C feeds to the bath. We simply do not run the bath taps and the shower at the same time.

This side-stepped unbalanced pressure issues. Was quite simple and cheap. Works fine at our level of expectations.

HW pressure from gravity alone is fine for everything else.

[Bob Mannix]

The dedicated sold feed from the loft is a "requirement" for power showers in the sense that it is recommended and the outlet from the loft tank must be BELOW that for the hot water feed. This is to prevent scalding if the header tank in the loft is exhausted (the hot water will run out first and you will get frozen instead.

[Roger Mills]

I can't see any point whatever in siting the pump next to the cylinder, and having to take a cold feed all the way down to it - and hot and cold shower feeds all the way back up again. With the pump under the bath, as originally planned, the cold feed only needs to come down to it from the attic. Putting an Essex flange in the cylinder with a dedicated hot feed to the pump is also an overkill in my view. With the cylinder on the ground floor, you've got a *lot* of head in the vent pipe at the takeoff point, and are very unlikely to suck it dry unless you've got an exceptionally powerful pump. I would simply take the hot feed from the existing 22mm pipe feeding the hot bath tap. That's what I did - and my cylinder is on the same floor as the bath rather than below it - and it's worked perfectly for nearly 20 years.

[Ian_m]

In my last house I acquired a shower pump under the bath, obviously fitted to try and improve the existing gravity fed mixer tap shower. It was a complete waste of time, issues were

- It was connected to the 22mm bath tap feeds but was only 15mm bore pump

- Made temperature uncontrollable, as was only a mixer tap, not thermostatic. Always too hot or cold.

- Used to cavitate very loudbly as I suspect the long lengths of supply pipe could not supply enough water.

- When cavitating temperature went all over the place.

- Would just start cavitation and going hot or cold just after applying shampoo.

- Could stop cavitating by turning taps down a bit, but then temperature fluctuated.

- If you flushed the loo or used a tap in the bathroom, temperature went all over the place again !!

- Pump was connected to the ceiling light electrics of the kitchen below the bathroom with no isolation switches or RCD's !!!!

- I got better showering success by removing the pump, fitting a new wider bore shower hose and bigger spray head.

Eventually replaced with a proper thermostatic shower valve on its own 22mm pipe work circuit. However first fit I put the pump in the loft and had cavitation/air lock issues ie shower wouldn't start immediately until all the air got out of the loop and had problems trying to keep it quiet as it vibrated the ceiling. Best success was placing it on paving slab in the loft.

However doing it properly, placing the pump on floor of airing cupboard (on a peice of paving slab + carpet to keep noise down), + appropriate air release valves fixed it once and for all..

So basically do it properly and you will have no issues......