Low mains pressure (or flow rate) with INSTALLED megaflo

Postby mark_doherty » Mon Sep 10, 2007 5:59 pm

We were unfortunately advised 18 months ago to go for a megaflo system. I have recently installed a shower and am VERY disappointed with the lack of either flow or pressure. I realise the best option would be to replace the mains pipe as a neighbour has done but wondered whether there was an alternative fix, such as a extra tank (coffin tank or similar) that I can install to increase the pressure and flow. The old header tank is still in the attic, though redundant. I have plenty of space to use up there. Neighbours say they have a power shower, allegedly with pumps installed... is this the case? I was under the impression that this was not possible with a megaflo.

BTW the mains pipe is a 25mm lead pipe. to replace it will be a nightmare, hence my question above. It runs under walls, through a narrow alley that I will have a job getting a digger of any sorts into and frankly the pebblyest soil i have ever come across, making hand dig it a right pain as it runs for over 100ft...

Any help here would be gratefully received
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Postby ynwa » Wed Sep 26, 2007 10:58 pm

If your water pressure is low then why did you go with a unvented direct system ? sounds like your were ill advised
low mains pressure surely means that you should of fitted an indirect vented system with cold water storage in the loft. Then you can add your pump on for the power shower.
"Unvented cylinders are limited by the 'power' of the mains water supply that feeds them, and in order to function properly require both adequate mains pressure and flow rate. Supply pressure should typically be in the region of 2 bar , preferable more, and capable of supplying the required flow rates."
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Postby mark_doherty » Thu Sep 27, 2007 9:05 am

thanks for your reply. The pressure is in the correct zone... its the flow rate. The leadpipe is approx 27mm and i have just discovered it joins a 15mm copper pipe, then goes through 2 90˚ bends within a foot of the lead and then through a stopcock (which could reduce down to 10mm within) and then into 22mm until the boiler and megaflo... I have purchased a straight lead to copper connector and a stopcock that stays 22 mm when open. This, hopefully with the loss of the bends will help. Worth doing before committing to a new mains pipe...

As for the recommendation, I am furious about it. Little I can do when a local, well reputable company advises you as to what to get and then, 18 months later you find it was terrible advice that will only mean extra cost to me... What do you do... I am a graphic designer... not a plumber... :(
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Postby bobplum » Thu Sep 27, 2007 7:09 pm

i would install a hot cylinder in the attic along side the cold tank and use the pump on this to power the shower
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Postby mark_doherty » Fri Sep 28, 2007 10:47 am

Didn't think I could do that...

the Megaflo is in the basement. the boiler on the grnd floor directy above it. I had heard that it may be possible to add a tank. That would be ideal. If so, there is space, right next to the megaflo which is right next to the shower.

Can I add a tank? Will it work with the megaflo and can I pump water from the extra tank to the shower?
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Postby ollie83 » Fri Sep 28, 2007 6:44 pm

you can use your old cold water storage tank to feed a neg head pump witch in turn feeds the megaflow. this is a good solution but the pump is around £300
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Postby rosebery » Fri Sep 28, 2007 9:45 pm

The Megaflo is mains fed therefore operates at mains pressure and if the mains pressure is OK then there's something else wrong somewhere.

Let's look at the shower then. Somewhere in the blurb it will tell you the minimum pressure that it is happy operating at. What is it's requirement compared with the 2 bar coming out of mains? What's to bet it's iro 3 bar?

Replacing your mains pipe seems a bit extreme it's not going to change the pressure your supplier is pumping it at or it's delivery rate either. I must say 2 bar seems a bit on the thin side irrespective of a megaflo installation. Don't have Thames Water as your supplier do you? They are using pressure management as a means of reducing leaks (of which they have gazillions) and energy consumption.

Is your stop cock fully open?

If you've measured the mains you must have a pressure guage. What is the pressure at the taps at bath and basin? What is the pressure at the shower? They should all be similar or thereabouts allowing for minor pressure drops across the different piping runs.

Has the flow out of the taps changed perceptibly as a result of installing the megaflo or is it the same as before?

Did you install a "full bore" iso vv on the shower or one of the standard ones?

Have you got a long run of 15mm to the shower or did you use 22mm reducing to 15 near the shower?

Change of tack - you can't pump mains. It's against the water regs and actually, technically, a pressure washer is illegal!! That's the limitation because the megaflo is mains fed - it's not the megaflo's fault you aren't allowed to pump it's output!

In short, I think you need to gather a lot more data to isolate the problem before taking decisions. Be careful it's not something you've done in relation to installing the shower otherwise any rocks you throw will come back with interest!

Talk to your water supplier and then your supplier/installer of the megaflo. I'm sure they'll be helpful. Did you tell the supplier / installer you were contemplating adding a shower later or discuss the possibility with him. Frankly you really can't blame him for "terrible advice" in this way if you've changed the rules downstream.

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