New mains or not

Chunkster · 14 Jan 2016

Greetings and Salutations.

Looking for some advice really, I've had a look around the forum for some ideas but would appreciate your help.

We need to replace our boiler and gravity fed hot water system. Now, I'd like to go for an unvented system but we don't have enough flow rate or pressure, British Gas were the only firm of 3 to actually check this.

So as expected I'm considering replacing the lead mains with a new, now there's 2 reasons for this:

1. Potentially solves my issues regarding the above.
2. Allows me to re-locate the stop cock which is currently under the hall floor.

Additionally, we're looking to convert the loft at some point this year with an en-suite so figure this will also have an impact. I understand that replacing the main may not solve the issue, I read a thread yesterday that suggested contacting the water board and asking them "to measure the flow rate in the street at your isolation point and put it in writing, this will be in litres/minute".

Thus, my question is this. If I can't have an unvented system for pressure/flow reasons, what are my options? BG suggested a Worcester Greenstar Highflow 440 CDi but I'd be interested in other opinions. The other 2 firms I got in, to be honest I wasn't overly impressed, as I mentioned, neither measured the flow rate/pressure and BOTH were quite happy to quote for an unvented system.

Thanks in advance, apologise if I've missed off a raft of information needed, ask away and I'll provide.

muggles · 14 Jan 2016

You'd be best off starting by finding out your static pressure. If that is very low then upgrading the main won't make much difference. If it's high then upgrading the main has more chance of success. Your local water authority may be able to measure the flow rate at the stopcock but it depends how good the access is to it.

If you're looking to have more than one bathroom running at once a combi would be inadvisable. Get the main properly investigated first and then it'll be easier to understand your options

Chunkster · 14 Jan 2016

Thanks for the reply.
I'll get in touch with the supplier, though looking at their website it seems they guarantee 7m Static head.

Would being on a water meter affect their ability to measure the pressure at the stopcock?

Madrab · 14 Jan 2016

Then they only guarantee .7 bar which for an un-vented system wouldn't be adequate, you're looking for at least 1.5bar and above.

No, it shouldn't affect the static pressure reading at your internal stop tap, checking the flow at the meter would be done if the static pressure reading was suitable. Did BG give you a note of their readings?

muggles · 14 Jan 2016

Not interested in what they guarantee, just what you've actually got. You can measure static pressure off an outside tap, or a washing machine valve

Chunkster · 14 Jan 2016

Madrab said:
Then they only guarantee .7 bar which for an un-vented system wouldn't be adequate, you're looking for at least 1.5bar and above.
No, it shouldn't affect the static pressure reading at your internal stop tap, checking the flow at the meter would be done if the static pressure reading was suitable. Did BG give you a note of their readings?

muggles said:
Not interested in what they guarantee, just what you've actually got. You can measure static pressure off an outside tap, or a washing machine valve

Unfortunately I can't remember accurately, but I think it was around 15 l/m and 1bar. I certainly recall him saying it wasn't sufficient.
So, with that taken into consideration and a combi a non-starter do I have any available options?

muggles · 14 Jan 2016

Chunkster said:
Madrab said:

Then they only guarantee .7 bar which for an un-vented system wouldn't be adequate, you're looking for at least 1.5bar and above.
No, it shouldn't affect the static pressure reading at your internal stop tap, checking the flow at the meter would be done if the static pressure reading was suitable. Did BG give you a note of their readings?

Click to expand...

muggles said:

Not interested in what they guarantee, just what you've actually got. You can measure static pressure off an outside tap, or a washing machine valve

Click to expand...

Unfortunately I can't remember accurately, but I think it was around 15 l/m and 1bar. I certainly recall him saying it wasn't sufficient.
So, with that taken into consideration and a combi a non-starter do I have any available options?

Find out what your STATIC pressure is. You appear to have quoted dynamic pressure, which is pressure when you have a tap running. What we need to know is the pressure when no taps are turned on

Chunkster · 14 Jan 2016

muggles said:
Chunkster said:

Madrab said:

Then they only guarantee .7 bar which for an un-vented system wouldn't be adequate, you're looking for at least 1.5bar and above.
No, it shouldn't affect the static pressure reading at your internal stop tap, checking the flow at the meter would be done if the static pressure reading was suitable. Did BG give you a note of their readings?

Click to expand...

muggles said:

Not interested in what they guarantee, just what you've actually got. You can measure static pressure off an outside tap, or a washing machine valve

Click to expand...

Unfortunately I can't remember accurately, but I think it was around 15 l/m and 1bar. I certainly recall him saying it wasn't sufficient.
So, with that taken into consideration and a combi a non-starter do I have any available options?

Click to expand...

Find out what your STATIC pressure is. You appear to have quoted dynamic pressure, which is pressure when you have a tap running. What we need to know is the pressure when no taps are turned on

Sorry, this is all quite new to me.
Will speak to the Water Board and see what they come back with.

Thanks again.

Madrab · 14 Jan 2016

You'll need to get someone in that can do a static test for you at one of the locations that muggles mentions, a reputable un-vented installer should be able to confirm if you have a suitable supply as part of their survey and then advise.

simond · 14 Jan 2016

If the pressure and flow was as you suggest, then the Highflow 440 will be a disaster.

Ironically, an unvented cylinder would work somewhat better than the Highflow with low pressures because the Highflow has a high resistance multi plate heat exchanger for the mains to fight its way through, whereas the cylinder has virtually no flow resistance.

If I've understood your post correctly, BG spotted the problem, and then shot themselves in the foot and reloaded. Nothing new there. BG are very good for the independents like me, with their advice.

You could fit an accumulator with a charger pump, then you can have the unvented and lots of water. The low static pressure is unlikely to be remedied by your water supplier, and a new pipe will not make any difference either in this regard.

Agile · 14 Jan 2016

Better not to "think what it was" as decisions should only be made based or facts.

An open pipe flow rate of 15 li/min becomes a dynamic flow rate of about 8 li/m @ 0.5 bar which as BG says is insufficient.

But you might be able to improve the flow rate with a 32 mm plastic supply to replace the lead. But you do really need a static of at least 1.5 bar.

The normal guidelines to get reasonable performance from an unvented are a minimum of 22 li/min @ 1.0 bar.

Tony

simond · 14 Jan 2016

Yes, the normal guidelines..... but the fact is that if you have 15 litres in, you get nearly 15 litres out.

The guideliines, as you put it, are purely there to manage the expectations of customers and some of the trade - who expect some magical impulse will push the water through faster than it normally comes up the road in the pipe.

I tell my customers that an unvented is a tin with a hole in the bottom where the cold water main is attached, and a hole in the top for the heated water to come out. That's it, there's no magic going on inside, whatsoever.

So, just like Hi-Fi systems, what you put in is what you get out.

Chunkster · 15 Jan 2016

Thanks again for all the information.
I've actually struggled to find a local independent that has the knowledge and expertise to have this conversation with.

I'm great at research and figuring out what I think I need, but of the firms I've had round so far 2 were happy to install an unvented system without checking pressure/flow rate.
BG were the only ones to check but then recommended the Highflow (which I now learn isn't so great), and the 4th told me a normal combi would suffice!! Even I know that normal combi won't be sufficient.
Add to that, the same bloke added that I could keep my gravity fed power shower with the new combi, he was quickly ushered out.

Chunkster · 12 Feb 2016

Update from me. Water company came out today and stated:

70m Head at the stop cock.
7bar at the tap and in excess of 25L pm at both!!

Kinda goes against what BG stated.

muggles · 12 Feb 2016

Sounds like you're fine for an unvented cylinder then!

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