Gravity fed water supply ... to switch or not

Discussion in 'Plumbers' Talk' started by Donut80, Sep 17, 2016.

  1. Donut80

    Donut80 New Member

    Hi,

    Recently bought a flat and considering options to improve shower and water pressure.

    Current setup is vented hot water cylinder with cold tank relatively low down in the 1st bathroom which isn't helping pressure (say 8ft height). Ideal Mexico standing boiler in the kitchen.

    One electric shower (mira sport) in flat right now that is dribbling out water. It is a 4 bed 2 bathroom flat so could use 2 showers or at least 1 working shower.

    Current thinking:

    1) Replace everything with combi boiler. Install thermostatic shower in 2nd bathroom.

    Pros: frees up some space and gives instant hot water. More efficient boiler

    Cons: possibly more expensive to maintain a combi, very expensive to install and flow will suffer if two showers.

    2) Switch flat onto cold water mains supply, bypassing cold water tank, to improve flow to taps, toilets and electric shower. Install a thermostatic shower in 2nd bathroom but keep this fed by cold water tank to avoid unbalanced water supply issue.

    Pros: cheaper option. Could do this as a temporary measure before combi switch later down the road.

    Cons: water pressure in 2nd shower likely to be poor without installing a pump

    Any thoughts on these ideas would be great, my plumbing knowledge is severely lacking so these options have just been cooked up over the last 2 weeks.

    It's quite an old flat so also bit worried about increasing pressure to the old pipes whether it be using a pump or connecting to mains. Any way of finding out whether a leaking disaster is around the corner without using the "wait and see" approach?

    Many thanks
     
  2. Hi Do.

    Can you explain more clearly where the cold tank is - is your flat on two levels? Is there a bathroom on each level?

    Also, why does your instant leccy shower only 'dribbling' out water? Is it because that's what they do, or is it because you cold mains water (which is what feeds them) is poor?

    What is you incoming cold mains pressure and flow like? For 'flow', open your kitchen cold tap fully into a pan for 10 seconds, measure the litres, times it by 6 to get 'litres-per-minute'.

    For 'pressure', post a photo of how much splashing occurred to your troos during this process. (Assuming you don't have a gauge).

    Do you 'want' to replace your current system? Ie - is it coming to the end of its life anyways? Or do you chust want to boost general performance?
     
    Donut80 likes this.
  3. Donut80

    Donut80 New Member

    Thanks for quick reply DA.

    The cold tank is in the first bathroom with the electric shower and the flat is all on one level, albeit it is a top floor flat which possibly doesn't help. The tank is a couple of feet above head height with no possibility of going higher.

    Thanks for clarifying re electric shower being mains fed, I thought it was coming through the cold water tank hence poor flow, this points towards poor mains or shower?

    Cold water tap in the same bathroom can be stopped on full power with a thumb. The one in the kitchen is more powerful and sprays when this is attempted - will post some embarrassing wet pants photos and measure flow tomorrow when I'm back home.

    What would be a good result? Ie is there a flow rate that would end up only leaving one viable option (or none!)?

    I only moved in recently and my instant thought was to want to replace the system as the Mexico "looked old", but having read up on similar issues (including posts on here) it doesn't seem like that was the smartest reaction.

    My overall goal is to have two reasonable showers available in the flat. I will check in with neighbour on same floor as me as well.

     
  4. I'd say there is no chance whatsoever that the leccy shower is supplied by the cold tank - certainly not unless it's pumped. Leccy showers generally require a min of 1 bar pressure (thereabouts) and that in turn requires around 10 metres of 'head'.

    The cold tap in the bathroom suggests it's supplied from the storage tank - stop water with thump - but I'd imagine that the shower has its own 15mm supply from the rising main.

    The pressure in the kitchen sounds more promising, so that does suggest a combi boiler has potential (it needs a decent mains pressure and flow) but bear in mind that a combi will only supply one item at a time in any case - so only one shower or hot tap running at any one time.

    A pressurised 'unvented' hot cylinder is another possibility. This is sealed and has no cold water tank supplying it, and is also pressurised using the mains pressure and a expansion vessel. The idea is that you have a ready supply of ready-heated hot water delivered under mains pressure backed up with the 'stored' pressure in the cylinder.

    Possibly the best solution, but will cost.

    Something you may wish to consider is to keep your existing system pretty much as it is but to gently boost the hot and cold supplies using 'home' pumps such as made by Grundfos. They are about £150 each and work automatically to boost the pressure by around 0.75 bar.

    You'd have one fitted on the cold tank's supply and another on the hot outlet from your existing cylinder (can you post a photo of these two items?). They should make your system almost like a decent vented system you'd get in a house - ie one where the cold tank would be up in the loft providing a good 'head'.

    With this, you'd replace your leccy shower with a normal thermostatic mixer type, and the new shower in the other bathroom would also be this type.

    You can fit much more powerful pumps, but my personal feeling is that they can feel artificial and be too 'gushing'; you turn on a tap and a trickle comes out, open it a bit more and a thrummmm starts in a nearby room and the tap starts to spray everywhere... :)

    That's probably unfair, but I understand these 'home booster' pumps are more natural and simply 'add' the pressure that would be there in a decent normal system.
     
    Donut80 likes this.
  5. Donut80

    Donut80 New Member

    So the kitchen tap (mains) is 12 litres per min. Bath tap in 2nd bathroom is also almost 12 litres per min despite coming off the cold tank. I'm basing whether or not something is connected to the tank based on whether I can hear it refilling or not.

    Seems strange that results are similar but I it looks like my flat is connected to lead mains supply which is reducing water flow significantly to the mains.

    The electric shower (mira sport 9kw) is 3 to 4 litres per minute. Is that just a function of the fact the supply is 12 so the electric shower can only provide 25pc of supply?

    Thanks for the pump tip. My hot water cylinder has a grundfos alpha 2 15-60 attached to it but not sure if that's doing the same thing, looks to just circulate water in the cylinder. Will a home boost pump help given supply pipe issue?

    Is a thermostatic shower in either bathroom a non starter given extra height that will create?

    Oh and pics are too large to upload apparently, will need to resize later.

    Thanks again.

     
  6. KIAB

    KIAB Super Member

    Rip the lot out & fit a combi or system boiler & unvented cylinder.

    PS: Valliant.:)
     
  7. Ok, so the cold 'rising' main is supplied at 12lpm (kitchen tap)? That is 'ok' but not great. It'll just about supply a combi boiler, but bear in mind there will be no flow left available to other taps as it does so - with two taps turned on, expect a very significant drop in flow from each.

    (NB - changing to a combi system usually means removing all your old stored water systems, cold tank and hot cylinder, so every tap is supplied from the mains.)

    I'd be hesitant in going for a combi system with such a borderline flow, so you'd need professional advice before doing so - a GasSafe plumber coming out and doing some tests. (Eg - the pressure this water is being delivered at is also important. Also, whether the flow drops at high demand times such as mornings).

    I forgot to ask - what storey level is your flat at?

    Photos - they need to be less than 2MB. If you are using a normal camera, chust set it to 3MP resolution. Otherwise use bit of software to reduce them - I sometimes use this: http://jpeg-optimizer.com/ It's free, doesn't have malware (that I'm aware of!) and seems to work well.

    The Grundfos pump your see at your hot cylinder is almost certainly your normal CH pump - it's the one that circulates the hot water from the boiler to the cylinder and the rads. Is there a 3-port motorised valve near it?

    Pumps - yes you can boost the incoming mains supply - there are special pumps for this - but they are restricted to what they can boost them by, and I think that's probably less than what you currently have anyway. (They aren't allowed to 'suck' too much 'cos they could affect the pressure in your neighb's flats...)

    The reason your leccy shower is only delivering 3 to 4 lpm is because that's all they can do - 9kw can only heat that much 'instantly'. It doesn't matter what its supply is at, it will only ever give a 3-4 lpm shower at that temp.

    So, you probably have three options:

    1) Possibly a combi boiler - but a pro would need to carry out flow and pressure tests to confirm. Also you'd need to discuss the pros and cons of such a system. Likely cost would be around £2.5k upwards to convert, including new boiler.
    2) A 'Megaflow' type system - a new sealed hot tank which is under mains pressure and which would replace your current cold tank and hot cylinder. It should be usable with your current boiler but a GasSafe would confirm. This needs a specialist installer - not every GasSafe can do 'pressurised'. Likely cost £2k upwards, I think (keeping existing boiler - add another £1k+ for a new one).
    3) If your existing cold tank and hot cylinder are suitable, then you could try boosting the flow from them using pumps. Likely cost around £500 upwards depending on the type of pump you'd go for. (The hot cylinder will almost certainly need a special take-off flange in the top too).

    Anyhoo, if you post photos of your current system, then hopefully pros on here can advise further, but at some point you'll need to call in the pros to check and advise further (but watch out for them 'pushing' their favourite system - listen carefully to what they have to say and ask Qs...)

    If you are a competent DIYer, you could fit the pumps yourself - leccy supplies needed to each (could be via an extra mains socket) and a bit of pipe cutting to fit the pumps. And the fitting of a Surrey/Essex/Whatevs flange (don't know the difference) in the top - the trickiest part.
     
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  8. KIAB

    KIAB Super Member

    Is your stopcock fully on, worth checking. can make a differnce.
     
  9. Donut80

    Donut80 New Member

    Thanks both for replies and summary of options. Pics attached of the boiler for info, cold water tank, hot water cylinder and pump. Stopcock is fully open (unfortunately). Flat is on the top floor (third) so I imagine that does not help at all.

    Neighbours are adamant that they have reasonable water pressure on combis. Given the cold water tank and the mains are similar flow rate, does it make sense to fit a thermostatic bath shower mixer and see how that flows? Would be relatively cheap test and give me an idea of how good the pressure would be on a combi after spending a small fortune.

    Bit confused about the lead piping. Neighbours again adamant that supply is no longer lead but the restricted flow and home report reference would suggest there might be an issue.

    I will take the advice and get a professional out to have a look. Advice on here has been invaluable, DA if you are based in Scotland and looking for a job then let me know ;)
     

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  10. Third floor will make a difference - the rising mains pressure will drop off significantly with height. However, yours seems to be pretty decent.

    When you say 'neighbours', are they on the same level as you, or below? If the same, then that's promising for fitting a combi.

    I wouldn't start fitting a thermo bath shower mixer until you have decided what sort of system you are going for - high (combi or unvented) or low (similar to what you currently have, perhaps with pumps to help) - because it will almost certainly not work properly.

    The reason for this is that you reckon your cold tank is at a height of 8'? Ok, when you stand in your bath, the shower head will be at a height of - ooh - 7' off the ground? So that means you'll have a shower 'head' of 1'. You gotta ask yourself, do you like being spat upon in a shower?

    It'll be a dribble at best, man. It'll only 'flow' if you sit down in the bath and hold the showerhead close to your chest...

    Time to call out a couple of pros, and listen carefully to what they suggest. They should hopefully be able to tell you if your rising mains is lead and, if it is, whether changing to MDPE will improve matters.

    They'll also test your mains pressure and flow and give an indication of the likely success of a combi - pretty good chance, I'd hope.

    You can discuss with them the pros and cons on an unvented 'pressurised' hot tank instead - will the extra cost be worth it?

    It would be nice to get that lump of a boiler off the floor anyway, wouldn't it?! It's exactly the type I had here when I moved in - a giant cast iron lump with a furnace under it. Nothing to go wrong - it'll last forever. But, man, it's hardly efficient - don't touch that flue unless you want to lose your skin...

    Oh, and - soz - I'm not in Scotland. And I'm not a plumber either :p
     
  11. Crowsfoot

    Crowsfoot Screwfix Select

    If you have poor mains pressure at times of peak usage the last thing you want is a combi boiler or unvented cylinder because both are dependant on a good consistent mains flow/pressure.
    A lot of todays sink taps are restricted so your type of test could give a false indication that the mains pressure is good when it really isn't.
    Like devs says you need to tread very carefully, get a experienced tradesman in before deciding what to do.
     
  12. Donut80

    Donut80 New Member

    Plumber came round earlier who agrees mains supply is poor but invited himself into my neighbours (again, also on top floor) and is confident based on their pressure that it would work. The old lead supply has been shut off and there is a new mains pipe (but this seems to be smaller than he was expecting).

    He said if it didn't work he would take the hit on installing a pressure booster directly to mains with a non return. I'd read that this wasn't possible but a quick google suggests there are options.

    Will keep you posted, thanks again :D

     
  13. Donut80

    Donut80 New Member

    Update on this: gravity system has been removed and replaced with combi. Thermostatic shower also installed. Water pressure is pretty borderline for the shower but does the job much better than the electric :D

    If I wanted to keep the electric shower but improve performance (was about 2 litres per mn earlier today) are my options speak to a plumber to check mains supply or upgrade to a 10.8kw (currently 9kw)? Or is that project doomed from the start...

    Thanks for all the advice.
     

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