System Or Combi

what about pressure?

 

A three storey house, any bedrooms on floor 2 going to be ensuite, I would go with a system boiler & unvented cylinder giving you hot water at mains pressure, presuming you have decent mains pressure.
Have a look at the Vaillant ecoTEC Plus system boilers.

 

flow rate seems poor. Did any of them check that the stopcock was fully open?

 

Stopcock in the house & the one outside your house.

Stopcock in house better replacing it with a full bore lever valve.

http://www.screwfix.com/p/full-bore-lever-ball-valve-15mm/80413

 

Its worth a check plus it might be better to measure the flow from something other than the kitchen tap like a ballofix valve or the likes of.

 

Good idea, but we don't know age of property, incoming mains could be lead for all we know.

 

If your water mains is lead some water companies offer a free lead mains replacement scheme,& replace usually with a 25mm or 32mm mdpe service pipe.

 

Ray, this is my understanding of these issues.

Combis - well, you know about them. Generally limited to only one outlet being successfully used at a time. And in your case, at 12 lpm, even one will only just be 'ok'.

So, unless you sort out your mains supply to improve wot comes in to your hoosie (yes, pressure is as important as flow - they are connected, but are different) then a combi is simply ain't gonna cut it. So if you told any plumber "I want at least 2 hot outlets to be able to run simultaneously..." and they still recommended a combi, then you should have serious doubts about them.

Ok, a System boiler is chust a boiler, one that is 'sealed' and doesn't need a wee F&E tank. It can be used with both vented and unvented hot cylinders. 'System' doesn't tell you what sort of hot supply you are going to have, but I'm assuming it's an unvented - pressurised - type the plumbers were talking about?

In which case, this isn't necessarily the solution either. Because an unvented cylinder is pressurised by the mains pressure only, so will only be as effective as the mains pressure. If your mains pressure is pants - if you can fairly easily stop your cold kitchen tap with yer thumb - then don't expect this solution to be totally effective. It'll be better than a combi, yes, but I suspect its 'effectiveness' could fall away rapidly after a 5 minute shower.

An unvented cylinder has a large 'balloon' inside it which is fill with pressurised air. The idea is that the rest of the cylinder fills with cold mains water under mains pressure and this compresses the air balloon right down to a much smaller size. That then creates a pressure 'reserve' in your cylinder - so when you open a hot tap you have both the cold mains pressure and this balloon shoving out the water! With only one tap turned on at around 12 lpm rate, then the mains will deliver this - the cylinder will remain 'full'. If you now open two taps to draw off, say, 24 lpm, then the stored pressure in that cylinder will drop rapidly 'cos the mains cannot keep it filled and pressurised, so the balloon will now expand and keep pushing out that hot water - until the balloon is fully expanded.

Ok? That's the principle (I think).

Right, the issue now is, what is your cold mains pressure? Because that is what ultimately pressurises your cylinder and gives you your flow.

Say your mains is 12 lpm (which it is...) and your pressure is good - eg 3 bar - then your cylinder will be fully pressurised (up to 3 bar) and will deliver LOTS of hot water to MORE than one tap with no issues (of course, ultimately the balloon will 'run out' and the pressure will drop accordingly, but you'll still have mains flow driving it at 12 lpm shared between the two taps). That's cool.

But if your cold mains flow is 12 lpm and with poor pressure - say less than 2 bar - then that balloon will never be fully compressed and the cylinder will never be at more than 2 bar pressure. When you then open two taps, you (a) won't get 24 lpm coming out and (b) the pressure capacity in that cylinder will fall off pretty rapidly as it empties.

The opposite would be the case if you had pants flow - say a pitiful 6 lpm mains - but GREAT pressure - 3+ bar. What would happen here is that your cylinder would take a relative 'age' to refill, but once full would be at 3 bar and then provide superb flow to two taps!

Bottom line, if you have barely adequate flow (yup - 12 lpm) and very poor pressure (we don't yet know), then even an unvented - pressurised - cylinder ain't going to be as good as you think.


Ironically, the best system for you (which I suspect you are trying to avoid) could be a CWS in the loft coupled with a 'normal' vented cylinder. With this, the ground and first floors at least will have unlimited supply, and even the top floor will be ok for anything other than a shower (in which case simply use a shower with a built-in pump).

So, as said in the posts above, you need a decent plumber who will first confirm whether your mains supply can be improved (dead easy - ask the neighbours...), test the pressure as well, and then give you some informed options.

 

I reckon his incoming mains is the issue, probably orginal lead,maybe iron, this needs to be sorted first.
But, a combi is the wrong choice here, definitely system boiler, but he needs to sort the pressure first.

 

Has no-one suggested an accumulator - big, expensive, and more to go wrong but can work out cheaper than a new mains pipe, assuming you have a good standing pressure and the space.

I'd always recommend a system boiler/unvented cylinder, but WB would be well down on the list of manufacturers to consider.

 

A accumulator is way down on my list,but as you say you need good standing pressure, if his mains is lead & his water company doing free lead mains replacement that's my first option.
I've known plumbers who have recommended accumulators, only to find after replacing mains, it's not needed.
Always liked Vaillant myself but as you say there are other makes to consider.

 

@JP. I did not believe unvented cylinders increased pressure as the forward pressure from the mains will be the maximum the system could attain ie 1 bar mains can't increase a tank beyond 1 bar. The flow rate would still sit at 12lpm and the pressure would be intake or 3 bar, whichever is lower?

Happy to be told that is not correct, just how I understand it.

 

Yes, I can't see any way an unvented cylinder can increase pressure, but what it can do is to maintain that cylinder's pressure for longer.

If you imagine a pressurised cylinder but one that has no 'balloon' in it, then the cylinder will be pressurised to the mains pressure - say, for example, a lowly 1 bar. Once an outlet is opened, however, that pressure will immediately drop, just as if a cold tap on the mains were opened. Open another outlet, and the pressure will drop further - so a much reduced flow. (Open a kitchen cold tap and then open another cold tap on the same mains; pressure - and flow - will drop.)

However, if you have a pressurised balloon inside that cylinder it will expand to fill that reduced pressure inside the cylinder as a tap is opened, so will therefore maintain that starting pressure.

 

I gave up on the third line...

 

Just for you, then:

So, unless you sort out your mains supply to improve wot comes in to your hoosie (yes, pressure is as important as flow - they are connected, but are different) then a combi is simply ain't gonna cut it. So if you told any plumber "I want at least 2 hot outlets to be able to run simultaneously..." and they still recommended a combi, then you should have serious doubts about them.

Ok, a System boiler is chust a boiler, one that is 'sealed' and doesn't need a wee F&E tank. It can be used with both vented and unvented hot cylinders. 'System' doesn't tell you what sort of hot supply you are going to have, but I'm assuming it's an unvented - pressurised - type the plumbers were talking about?

In which case, this isn't necessarily the solution either. Because an unvented cylinder is pressurised by the mains pressure only, so will only be as effective as the mains pressure. If your mains pressure is pants - if you can fairly easily stop your cold kitchen tap with yer thumb - then don't expect this solution to be totally effective. It'll be better than a combi, yes, but I suspect its 'effectiveness' could fall away rapidly after a 5 minute shower.

An unvented cylinder has a large 'balloon' inside it which is fill with pressurised air. The idea is that the rest of the cylinder fills with cold mains water under mains pressure and this compresses the air balloon right down to a much smaller size. That then creates a pressure 'reserve' in your cylinder - so when you open a hot tap you have both the cold mains pressure and this balloon shoving out the water! With only one tap turned on at around 12 lpm rate, then the mains will deliver this - the cylinder will remain 'full'. If you now open two taps to draw off, say, 24 lpm, then the stored pressure in that cylinder will drop rapidly 'cos the mains cannot keep it filled and pressurised, so the balloon will now expand and keep pushing out that hot water - until the balloon is fully expanded.

Ok? That's the principle (I think).

Right, the issue now is, what is your cold mains pressure? Because that is what ultimately pressurises your cylinder and gives you your flow.

Say your mains is 12 lpm (which it is...) and your pressure is good - eg 3 bar - then your cylinder will be fully pressurised (up to 3 bar) and will deliver LOTS of hot water to MORE than one tap with no issues (of course, ultimately the balloon will 'run out' and the pressure will drop accordingly, but you'll still have mains flow driving it at 12 lpm shared between the two taps). That's cool.

But if your cold mains flow is 12 lpm and with poor pressure - say less than 2 bar - then that balloon will never be fully compressed and the cylinder will never be at more than 2 bar pressure. When you then open two taps, you (a) won't get 24 lpm coming out and (b) the pressure capacity in that cylinder will fall off pretty rapidly as it empties.

The opposite would be the case if you had pants flow - say a pitiful 6 lpm mains - but GREAT pressure - 3+ bar. What would happen here is that your cylinder would take a relative 'age' to refill, but once full would be at 3 bar and then provide superb flow to two taps!

Bottom line, if you have barely adequate flow (yup - 12 lpm) and very poor pressure (we don't yet know), then even an unvented - pressurised - cylinder ain't going to be as good as you think.


Ironically, the best system for you (which I suspect you are trying to avoid) could be a CWS in the loft coupled with a 'normal' vented cylinder. With this, the ground and first floors at least will have unlimited supply, and even the top floor will be ok for anything other than a shower (in which case simply use a shower with a built-in pump).

So, as said in the posts above, you need a decent plumber who will first confirm whether your mains supply can be improved (dead easy - ask the neighbours...), test the pressure as well, and then give you some informed options.

 

Anyhoo, it was for my mate Ray, not yooooooooo