Unvented system low pressure in low

[Ricky786]

New unvented system fitted however all the taps on the ground floor and middle floor have 12l per min but in the loft is 4L. A considerable drop to what was before around 8L per min. Any ideas what can be done to cause this drop and what can I do to improve the flow rate. Really appreciate it

 

[flameport]

Pipe to loft restricted / blocked, some valve not fully opened or broken internally, loft taps are defective / blocked / junk.

 

[Ricky786]

Pipe to loft restricted / blocked, some valve not fully opened or broken internally, loft taps are defective / blocked / junk.

Is there anything you would recommend to fix ?

 

[Madrab]

what can I do to improve the flow rate

Get the installer back in and get him to sort it. If it's a new install then that really should be their responsibility. They should have checked tested all the outlets before the job was signed off.

Another query, do you know your mains dynamic pressure and flow, 12L/Min is rather on the low side for an unvented especially one that size, how many bathrooms/showers?

 

[Ricky786]

Get the installer back in and get him to sort it. If it's a new install then that really should be their responsibility. They should have checked tested all the outlets before the job was signed off.

Another query, do you know your mains dynamic pressure and flow, 12L/Min is rather on the low side for an unvented especially one that size, how many bathrooms/showers?

I’m not sure as the main dynamic pressure. But middle floor taps and bath taps are about 12l and upstairs is really considerably low. They are saying that it’s nothing that they have done. I’ve explained to them that the pressure just can’t just miraculously go down that much. They also mentioned that it could be a potential pipe sizing issue and that 22mm pipe needs to be installed instead of the 15 that leads up to the loft taps.

 

[Madrab]

They are saying that it’s nothing that they have done. I’ve explained to them that the pressure just can’t just miraculously go down that much. They also mentioned that it could be a potential pipe sizing issue and that 22mm pipe needs to be installed instead of the 15 that leads up to the loft taps.

Wrong Wrong Wrong Wrong.

15mm pipe will happily deliver well over 12L/Min (approx 21L/min @ 2m/s) as long as there is suitable dynamic pressure to drive it. What does happen as the flow exceeds 1.5-2m/s then it does start to get noisy. If there isn't enough dynamic mains pressure to drive it upstairs properly then a question would be raised as to the suitability of an unvented cylinder being installed in the first place. It is normally a critical understanding before work should proceed at it should be known.

You are correct, flow (not pressure) shouldn't just miraculously drop if nothing else has changed.

That being said if they haven't done anything to the system and if everything was installed correctly then that shouldn't affect the flow to upstairs either but given the only thing that has changed is the addition if the unvented then with everything being equal it has to be something to do with the install.

They should at least come and investigate and not just dismiss it out of hand, as suggested it could be something as simple as a restriction, valve half closed or similar

 

[Ricky786]

Wrong Wrong Wrong Wrong.

15mm pipe will happily deliver well over 12L/Min (approx 21L/min @ 2m/s) as long as there is suitable dynamic pressure to drive it. What does happen as the flow exceeds 1.5-2m/s then it does start to get noisy. If there isn't enough dynamic mains pressure to drive it upstairs properly then a question would be raised as to the suitability of an unvented cylinder being installed in the first place. It is normally a critical understanding before work should proceed at it should be known.

You are correct, flow (not pressure) shouldn't just miraculously drop if nothing else has changed.

That being said if they haven't done anything to the system and if everything was installed correctly then that shouldn't affect the flow to upstairs either but given the only thing that has changed is the addition if the unvented then with everything being equal it has to be something to do with the install.

They should at least come and investigate and not just dismiss it out of hand, as suggested it could be something as simple as a restriction, valve half closed or similar

The only thing they said to have done was extended the blue pipe to were the cylinder now is and changed the route slightly of the hot and cold downstairs. Everything else was as it was before. How the flow is considerably low. Is there anything I can do to test the pressure and then I can say to them that this is the issue and needs sorting for example. Or just anything you would recommend I can do to show and tell them that’s it’s an issue that they have caused

 

[Madrab]

Is the blue MDPE the mains for the house? I really don't know why installer don't install a pressure gauge on the supply when an unvented is going in.
If you have an outside tap, then you could buy a screw on gauge and do some testing. Also use that to test for flow. TBH though, all this should have been done before any works started.

To get the best out of an unvented system I would never recommend it to be installed on anything less than 2.5bar @ 25L/min dynamic, especially if it is feeding more than one shower/bathroom

 

[Ricky786]

Is the blue MDPE the mains for the house? I really don't know why installer don't install a pressure gauge on the supply when an unvented is going in.
If you have an outside tap, then you could buy a screw on gauge and do some testing. Also use that to test for flow. TBH though, all this should have been done before any works started.

To get the best out of an unvented system I would never recommend it to be installed on anything less than 2.5bar @ 25L/min dynamic, especially if it is feeding more than one shower/bathroom

Yes that blue pipe is for the house was extended to the cylinder. I can a gauge and I can do the testing. If the pressure at the mains is low how would that be that the both floors have a decent flow rate but the loft don’t? It’s really weird how they didn’t install a gauge

 

[Madrab]

If the pressure at the mains is low how would that be that the both floors have a decent flow rate but the loft don’t? It’s really weird how they didn’t install a gauge

If everything is as it should be i.e. no blockages, pipe works all clear, nothing else has been changed etc then the defining factor is all to do with pressure really. As water is pushed vertically, it requires more pressure to maintain a given flow as the height increase.

To give an basic example - if there is 1 bar of sustained (dynamic) pressure at ground level (10m Head) on an open ended pipe, then @ 5M height there will be a reduction of 0.5 bar dynamic of available pressure from that same open ended pipe, as it has used 0.5bar (5m head) to push the water vertically that high. Therefore the pressure exiting that open pipe would now be 0.5bar and that's not taking friction/turbulence into consideration

That also doesn't take into consideration any fittings, bends valves, lengths/diameter of pipe etc - every fitting, bend, valve, meter of pipe, outlet etc will sap some of that available pressure due to turbulence/friction, reducing the pressure and flow at the outlet further. So the higher and further you go, the less there will be at the outlet. Hence why unvented cylinders really have a lower limit to where the available mains pressure and flow is no longer suitable.

All that being said though, that still doesn't take away from the fact that there was 9L/Min before the install and now there isn't.

 

[Ricky786]

If everything is as it should be i.e. no blockages, pipe works all clear, nothing else has been changed etc then the defining factor is all to do with pressure really. As water is pushed vertically, it requires more pressure to maintain a given flow as the height increase.

To give an basic example - if there is 1 bar of sustained (dynamic) pressure at ground level (10m Head) on an open ended pipe, then @ 5M height there will be a reduction of 0.5 bar dynamic of available pressure from that same open ended pipe, as it has used 0.5bar (5m head) to push the water vertically that high. Therefore the pressure exiting that open pipe would now be 0.5bar and that's not taking friction/turbulence into consideration

That also doesn't take into consideration any fittings, bends valves, lengths/diameter of pipe etc - every fitting, bend, valve, meter of pipe, outlet etc will sap some of that available pressure due to turbulence/friction, reducing the pressure and flow at the outlet further. So the higher and further you go, the less there will be at the outlet. Hence why unvented cylinders really have a lower limit to where the available mains pressure and flow is no longer suitable.

All that being said though, that still doesn't take away from the fact that there was 9L/Min before the install and now there isn't.

Thanks for that really detailed answer and helps a lot to understand. Would there be anything I can do help increase the pressure to then get a better flow rate for hot and cold in the loft taps and bath

 

[Madrab]

As suggested - you need to know what you have to start with. If you are getting 12L/min on the ground and 1st floor then a drop of 8L/min over another say 2m is a lot.

The pressure figures are important to know and then it's down to why there is such a drop in flow up to the second floor. Again as suggested in post #2, time to check for pipe blockages/restrictions, failed valves etc but that still comes back to the installers and they should be fault finding and not just saying, oh install a larger pipe!