Low mains water flow stumped!

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Hello,
Since moving into a different house we have had an issue with the mains water low flow which is so bad the shower running off combi boiler will turn to a trickle if anything else is using water e.g. toilet cistern, washing machine etc. I also can barely use my pressure washer as the garden tap can't supply enough for it.

Bear with me I'll detail what i've found/done so far.

1) First thing I noticed when we moved in was the stop tap on the meter under the pavement had moved so that you couldn't turn it off, contacted water company and they had it replaced with a modern 1/4 turn plastic one. I had hopes the old one wasn't fully opened but this made no difference.

2) Water company sent "a guy" out to test flow, he took off the meter and put a tap straight on it and there was loads of flow. Visually it was obviously a lot more than what I get in the house. I can't remember the figures but it was basically maxing out the little measuring device they have where the water pours out the side. Ok so good pressure up to that point.

3) Replaced our internal stop tap with a new one. Once removed, the old one it was gunked up with plumbers mate or something and the inlet side was 3/4 blocked. Brilliant I thought that must be the cause. No change. Balls!

4) I then bought a water pressure gauge - measured static 3 bar at the garden tap. Not bad but good enough as far as I understand?

5) I then measured flow at the garden tap so I could put a number on it - 6.5LPM consistently, across multiple measurements at different times of day.

6) I then put a hose straight onto the outlet side of the internal stop tap to measure flow there in case there was some blockage in our internal pipework - again 6.5LPM.

7) I then removed the internal stopcock completely and measured flow directly from the mains pipe (20 or maybe 21mm external diameter black plastic pipe) where it was slightly better at around 7.75LPM (makes sense as it's not having to go through any 15mm copper pipe or bends).

Just to see if there was any obvious blockage I shoved some stiff washing line wire down the mains line and gave it a good wiggle around. Each time I got to around 5m before it seemed to come to a stop. However there was a lot of friction at that point so hard to say if it was a definite stop or just too much friction for the wire to take without buckling. This would take it to roughly just outside the exterior wall of the house.

By process of elimination it seems the issue must be between my stop tap and the mains meter, right?

Now this is where it gets weird.

When I turned everything back on - loads of flow. It was obvious visually but I measured twice at the garden tap and got 9.75 and 9.5LPM. However, the flow doesn't stay that high! Over the course of a few hours of normal use, it will drop back down to 6.5LPM again.

The same thing happened when I first changed the stop tap, and when I have turned the water off other times I have also thought the flow seemed better. However as I wasn't measuring flow back then I didn't think too much of it. I've not managed to narrow it down to whether it's the mains stop tap or the internal stop tap which does it.

So, what gives! I am not a plumber but I am absolutely stumped. Why would turning off the stop tap increase flow, but only temporarily?

My next step was to possibly dig up the water main in the front garden to see if it is plastic all the way or whether it goes into lead (house is 1930's) somewhere between the two (for some reason).
 
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When I turned everything back on - loads of flow. It was obvious visually but I measured twice at the garden tap and got 9.75 and 9.5LPM.
9 litres/minute is not loads of flow - it's rubbish.

I can't remember the figures but it was basically maxing out the little measuring device they have where the water pours out the side.
Most of those go up to around 20 litres/minute, so it was more than that.

Most likely is that the pipe from the meter to the house is restricted in some way, such as blocked internally or crushed. There is also the possibility of it leaking underground.
 
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It would be useful to know the diameter and material of the suspect pipe.

Especially if it is lead, since the house is 1930s

There may be an old forgotten stopcock just inside your garden, probably buried or paved over

Simplest cure may be to dig a trench and lay a new piece of plastic pipe in a larger size, with new larger stopcock to suit.

The trench need not follow the same route as the old pipe.

Some water co's offer assistance when replacing lead pipe
 
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Should have asked the water guy what the flow was and then you would have had an idea of actual flow losses from boundary box to stop cock
 
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Did they change the meter ?
We had a similar problem, water board did flow test said we had a leak from road to house. Replaced pipe from pavement to meter in kitchen,still low pressure .
Water board came back out to find grit in meter. Replaced meter with new one,pressure now fine.
Work had been carried out in the street few weeks prior and deposited grit in my meter.
 
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2 things that you need to check again, for the poressure gauge to the outside tap and whiilst that's open, open 1 internal tap then 2 and see how it drops, that gives you a dynamic figure which is a key reading. Same with measuring the flow, test it with than one outlet open at a time.

If you say that the flow drops after a little while, then as suggested it sounds like a blockage/restriction somewhere between the outside tap and the internal pipework.

It would have been good to ask the supplier to give you flow and pressure figures on the mains to allow for a direct comparison.
It would be useful to know the diameter and material of the suspect pipe.

20 or maybe 21mm external diameter black plastic pipe
 
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The flow cup used would be 25 litres per minute, If your getting 9 litres per minute at best there is a big difference and definitely something wrong with the pipe coming in, have you checked for any other stop taps on the pipework, underfloor boards, it may have been moved in the past and the old one left in or maybe another one in your garden as black poly pipe normally gives a better flow unless there is a leak on the line which you can check if you have a water meter fitted (it would constantly move even if no water was been used in the property) or the pipe has been squashed or kinked.
 
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I came across this a few months ago, after a lot of pain, I found a hidden stopcock buried behind kitchen units.
As someone said above.
 
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2 things that you need to check again, for the poressure gauge to the outside tap and whiilst that's open, open 1 internal tap then 2 and see how it drops, that gives you a dynamic figure which is a key reading. Same with measuring the flow, test it with than one outlet open at a time.

If you say that the flow drops after a little while, then as suggested it sounds like a blockage/restriction somewhere between the outside tap and the internal pipework.

It would have been good to ask the supplier to give you flow and pressure figures on the mains to allow for a direct comparison.
I would suggest to let a dribble of water flow from where the P.gauge is attached because if a non return valve fitted then the pressure reading may not be accurate due to trapped pressure.
 
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Did they change the meter ?
We had a similar problem, water board did flow test said we had a leak from road to house. Replaced pipe from pavement to meter in kitchen,still low pressure .
Water board came back out to find grit in meter. Replaced meter with new one,pressure now fine.
Work had been carried out in the street few weeks prior and deposited grit in my meter.

That must have been very frustrating for you, but interesting to know. I did think that there could be a restriction in the meter as the water board removed it to do their flow test. I also know next door have changed their supply pipe (prior to us moving in) so there has been the opportunity for debris to be introduced.

2 things that you need to check again, for the poressure gauge to the outside tap and whiilst that's open, open 1 internal tap then 2 and see how it drops, that gives you a dynamic figure which is a key reading. Same with measuring the flow, test it with than one outlet open at a time.

If you say that the flow drops after a little while, then as suggested it sounds like a blockage/restriction somewhere between the outside tap and the internal pipework.

It would have been good to ask the supplier to give you flow and pressure figures on the mains to allow for a direct comparison.

Thank you I will test dynamic pressure/flow tomorrow and report back. I will also try and get flow/pressure figures on the meter from water board.

The flow cup used would be 25 litres per minute, If your getting 9 litres per minute at best there is a big difference and definitely something wrong with the pipe coming in, have you checked for any other stop taps on the pipework, underfloor boards, it may have been moved in the past and the old one left in or maybe another one in your garden as black poly pipe normally gives a better flow unless there is a leak on the line which you can check if you have a water meter fitted (it would constantly move even if no water was been used in the property) or the pipe has been squashed or kinked.

I think due to being able to put 5m of wire down the incoming main which takes it to outside of the property if there is an old stop tap it must be buried in the garden/under the patio which is no good.

I have checked for leaks and the water meter did not move over night when the internal stop tap was closed which I think rules that out.

The other small detail is that there is a 5m tall apple tree in the vicinity of where I would expect the supply pipe to run, I don't know how resistant poly is to crushing with roots but I imagine not very as nature tends to win fights like that over time?

Thanks for the other replies. Think I will get the water board back out to get pressure/flow readings and check for a faulty meter first as that doesn't cost me anything!
 
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More pressure/flow readings:

Flow from garden tap - 6.5LPM
Flow from garden tap when toilet is refilling - 4.75LPM
Flow from garden tap when kitchen tap is on - 4.75LPM

Pressure always measured at garden tap:
Garden tap only - 3 bar
When kitchen tap is on - 2 bar
When downstairs sink is on - 1 bar (this is on a shared 15mm spur with the garden tap)
When kitchen tap and downstairs sink is on - 0.5 bar
When toilet is refilling - 0.7 bar

Not sure what this means for my issue?
 
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Means nothing unless someone on this site understands and can calculate frictional head loss along lengths of pipe whilst taking flow and fittings and pipe size into account which nobody does. Pressure and flow rate at boundary box is your starter for 10
 
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I've got a 1952 iron main with 40 litres a minute and 4.5 bar of pressure theres a 225mm main one street over
 
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Your numbers indicate a restriction in your supply pipe somewhere. 3 bar static pressure is good but your flow rates are completely inadequate.
The apple tree is a bit of a red herring- placcie pipe (being flexible) will generally move around root growth.
You'll end up either digging the old pipe out (to find an old stoptap or a corroded coupler) or just digging a new trench for 25mm mdpe. Once you've done that you can look again at internal supply arrangements.
 
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Water board sending someone out in a couple weeks, I guess the only thing I can see if they can rule out is the grit in the meter. Seems unlikely but worth doing I think before I start with the disruption and expense of laying a new supply/digging.

Your numbers indicate a restriction in your supply pipe somewhere. 3 bar static pressure is good but your flow rates are completely inadequate.
The apple tree is a bit of a red herring- placcie pipe (being flexible) will generally move around root growth.
You'll end up either digging the old pipe out (to find an old stoptap or a corroded coupler) or just digging a new trench for 25mm mdpe. Once you've done that you can look again at internal supply arrangements.

When you say corroded coupler do you mean where someone would have left a section of the original lead supply in and joined it onto the plastic pipe I can see? Is it not unusual to do this?
 

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