Pressure problems... Help!

[BuGsBuNnY]

Bit of background:
We have purchased a newbuild property which comes with a gravity fed hot water system and a pumped central heating system. Bear in mind I am a complete plumbing novice, and this is my understanding from my research online and by asking other people. The boiler is an IDEAL HE 18 (I think that it is a condensing boiler) and there is a massive cold water tank in the loft, a smaller cold water tank next to it which I think is the header tank, a hot water cylinder in the airing cupboard, and a central heating pump in the same cupboard.
I will get some pics to show you exactly how the system is plumbed in tomorow.
In the property, there is one WC downstairs, 2 ensuite showers upstairs, and a bathroom upstairs.

The problem:
The pressure/flow on the ground floor is fine.
We have low pressure on the first floor.

The bathroom filler tap has more than adequate pressure/flow.
Both of the showers have minimal pressure/flow.
Both of the basin taps have minimal pressure/flow.

The builder's plumber checked the flow rate and said it's adequate, which it aint. The taps are providing 4litres of hot water (I assume that is per minute) but if you run the bath filler at the same time, that drops to less than half.

Notes:
1)I don't know what the mains pressure is, it's on my list of questions for Monday.
2)From my research, the solutions are:
i)A pump (salamander suggested a RHP75 for the whole house) However, I visited a friend's house to see/hear a pump in operation, and although it's quiet enough, the vibrations are horrible.
ii)Changing the system to a fully pumped solution.
The builder's plumber mentioned something about changing the hot water cylinder or adding something to it, and also adding an external vent which is a pain as the chipboard will need to be lifted. This is something I don't fancy doing to a brand new house. A friend also suggested that an unvented cylinder can be used? (I don't know anything about this)

Can you please help as to what the best solution would be and a rough idea on cost for the conversion to a fully pumped system?
I don't want to change the boiler, but have no problems with changing the hot water cylinder and/or isolating and throwing awaythe cold water tanks in the loft.

Many thanks!

 

[Elkato531]

The low flow on the bathroom taps is because you have a low pressure tank fed installation. I would not be surprised, as its a new build, if its all been plumbed in 15mm plastic. This is ok on mains pressure systems but will not deliver enough water on gravity installations.

I would get back onto builder and demand a system that works properly. Ask him if he'd be happy with it in his house.

You options are to repipe the system properly. This will give better flow but your shower may still be poor. Will mean lifting floors which with chipboard is a real pain or taking down ceiling and doing it from underneath another big pain.

Whole house pump. Probably cheapest option but as you've identified, could be noisy.

Unvented cylinder. Probably the best option but not cheap and may not be possible for it to go in your existing airing cupboard.

Install a combi boiler and adapt the system to suit. This may be the best solution in terms of cost and disruption but may not give enough hot water to run several outlets at once.

Both unvented and combi would require sufficient mains pressure and flow which you would have to check before hand.

 

[BuGsBuNnY]

The builder knows in no uncertain terms that we are not happy. Unfortunately, although the pressure is not to fully pumped levels, the flow rate from all outlets conforms to their minimum which is 4ltrs/min. I intend to challenge that as once a second outlet is opened, the flow rate is dropping to around 2lt/min.

I have been told that the water system is a mixture or 28 and 22mm pipe, which is what I can see underneath sinks at least. No way to check showers other than take the builder's word.

The central heating pipes are smaller in diameter from what i can see.

Apparently, combi is out of the question as it will never be able to supply all outlets (so I have ben told, I don't have sufficient knowledge to calculate requirements against a combi specification to confirm)

What mains pressure is considered sufficient?
Why would an unvented cylinder not be able to go in the airing cupboard? (If you are reffering to space availability, there is plenty of space in there.)

 

[dextrous]

An unvented cylinder may take up too much room - you really need someone round who knows what the final dimensions will be based on knowledge and experience. We don't know how much space you have, as you've not told us.

 

[Hugh Jaleak]

Basically as I read it you have bought a new house and the plumbing does not seem to offer the performance you would expect. Personally I dont see why you should be looking to spend any more money getting it sorted out. The builder has sold you a house where the plumbing is not fit for purpose, as Elkato531 has said, get them back to sort it out properly! I appreciate you dont really want to start dismantling a brand new house but can you live with the status quo? The builder should really sort out your concerns to your satisfaction and return the property to its original condition at his expense.

If its a new build then the Boiler will have to be the condensing type, its mandatory now. However Ideal boilers dont seem to live up to their name, a quick search on here will throw up all manner of unhappy Ideal boiler owners.... The central heating/hot water side will be a fully pumped system. Cold supply to the taps is mains fed, and the hot water supply to the taps is gravity feed. (The water that is heated by the boiler for the radiators and to heat the hot water cylinder is entirely seperate from the water than comes out the taps.)

I would assume a new build has reasonable mains water pressure and flow, so an unvented cylinder may go some way to easing your problems. However they are not cheap, need to be installed by someone with a G3 ticket for unvented work, and require an annual safety check, although this could be tied in with a boiler service if you can find an engineer who is Gassafe and G3 registered.

 

[Elkato531]

Unvented cylinder may go in the airing cupboard but it needs a safety discharge to run to outside with a continuous fall. This is what can give problems with siting them.

If your hot water pipework is in 28mm and 22mm then you should be getting better flow than you are. It is possible that there are air locks in the pipes.

Another possibility is that the taps are designed for high pressure and changing them could help. The manufacturer should be able to let you know recommended minimum pressure.

BTW fully pumped refers to the heating/hot water system. You should have this already as its part of building regs. It means that the heating pump pushes water round your rads and through the coil in your cylinder and is controlled by motorised valves. It doesn't affect the flow from your taps.

 

[Hugh Jaleak]

I would be extremely surprised if 28mm has been used anywhere other than from the cold storage tank in the loft to the cylinder inlet. 22mm would be used to supply a bath on a gravity supply, but for all other appliances then 15mm is the norm. Sink and basin taps are 15mm connections so in the rare event 22mm was used, it would have to be reduced down to 15mm before the taps.

 

[BuGsBuNnY]

I think I am starting to understand the installation a lot better.

Taps are upgraded mixer type, the builder has said that its is possible that they are at fault, and have escalated to the manufacturer for advice.
I will try to find the technical drawing and info on minimum pressure.

This would not affect the showers though, which are still poor.

What is the relation, if any, between flow rate / pressure ? Is there a formula that connects the two?

 

[Hugh Jaleak]

Mains pressure will only affect the cold taps. You said you have adequate pressure/flow downstairs, its the upstairs where you have an issue. Am I right in thinking the hot and cold taps upstairs have poor flow/pressure?

 

[BuGsBuNnY]

Quite right. Oddly enough, all upstairs are poor apart from the bathroom filler, which is fine and visibly better than any others. Then again, its about 30-40cm lower than the basin taps.

Having said that, cold is slightly better than hot throughout the house.

 

[Hugh Jaleak]

The bath should be fed in 22mm from the cylinder on a gravity supply, so seems ok. It does seem odd though the cold is only marginally better than the hot throughout, usually cold is mains fed which will give superior pressure/flow than the hot. I can only suggest you continue to argue the toss with the builder, something isnt right and he needs to sort it out to your satisfaction at his expense. Without seeing the pipework, most of which is no doubt buried under the floors, its difficult to ascertain what might be causing the poor output at the taps.

 

[BuGsBuNnY]

The taps require a minimum of 0.5 bar of pressure according to the manufacturer's website.

Is there any way to accurately measure mains pressure?

 

[WDIK]

Is there any way to accurately measure mains pressure?

yes.
but the difference, between, standing pressure and full flow pressure, is radiclly different.
if the standing pressure is high but falls at flow then the pipework is under sized.

 

[TicklyT]

To calculate the static pressure of a gravity system, measure the vertical distance from the base of the cold storage cistern to the water outlet in Metres, and divide by 10 (1 Bar = 10.19716 Metres of water).

A typical gravity system (storage tank in loft above first floor bathroom, kitchen on ground floor) will give about 0.15 - 0.2 Bar at the bathroom taps, and about 0.4 - 0.5 Bar at the kitchen taps.

The pressure at a shower head in a bathroom may be lower than 0.1 Bar.

 

[Elkato531]

TicklyT is correct. If the basin taps require a minimum of 0.5bar, the cold water storage would need to be approx 5m above the taps. This is very unlikely to be acheivable with an upstairs bathroom in a 2 storey house.