Low flow rate (5L/min) at electric shower, 30L/min at stopcock

[UserSteve]

Hello,

I have quite low flow rate for my electric shower (a piddling 5L/min), and would like some tips or advice about how to solve or find the cause. I would like a flow rate of about 12L/min.

Here is my set-up:

Standard gas boiler (not a combi) in the kitchen, have cold water tanks in the loft, and have the hot water tank & immersian heater in one of the upstairs bedrooms.
Bottom of loft water tanks are 1 meter above the shower pipe.
Mira 9.5kW electric shower.
10mm cabling to the electric shower, and the circuit can handle up to 14kW.

Here is what I have found out so far:
Anglian Water measured the pressure and flow rate at the outside water meter at 2.2bar and 40L/min (which is very good).
Anglian Water engineer suggested the low flow rate was due to a corroded stopcock.
I replaced the stopcock which did not change the flow rate anywhere in the house.
I measured the flow rate at the stopcock under the sink to be 30L/min (ran a hose off it into a bucket. 7.5 litres in 15 seconds).
The mains pipe is a standard blue plastic 22mm pipe.
All the pipework after the stopcock is 15mm.
With all appliances turned off and all possible valves turned off, the flow rate at the outside tap is 18L/min.
With all appliances turned off and all possible valves turned off, the flow rate at the kitchen sink cold tap is 10L/min.
Distance between stopcock and kitchen sink is less than one meter.
The flow rate of the cold water tap at the bath is 12L/min.
The flow rate of the cold water tap at the bathroom sink is 8.5L/min.
The flow rate of the cold water inlet pipe into the electric shower is 5L/min.
The bathroom & electric shower is about 4-5 meters above the stopcock.

Between the stopcock and kitchen sink, the water flows through two 15mm isolation values (the standard ones with the flathead screw), and five 90-degree bends.

Can anyone suggest why there is such a drop (from 30L/min to 5L/min) in flow rate?

I have had a plumber suggest that a better flow rate could be achieved be replacing the 15mm pipework up to the bathroom with 22mm pipework. But he could not guarantee that after this work was completed that the flow rate would be any better.

So it seems a black art. Any suggestions welcome.

 

[ShaunCorbs]

Kitchen tap 10lpm restricted ?

Electric shower they are around 5-6lpm because it’s like a big kettle trying to heat up the water etc

 

[UserSteve]

Kitchen tap 10lpm restricted ?

Electric shower they are around 5-6lpm because it’s like a big kettle trying to heat up the water etc

Shaun, I measured the flow rate is 5L/min at the shower cold water inlet pipe. That is BEFORE the water goes into the shower unit itself. So any effects of the shower unit and its heating method itself is irrelevant to my measurements.

What do you mean by "Kitchen tap 10lpm restricted"?
The kitchen tap is about 2 years old, and both the hot and cold taps have those flexi pipes connected to the 'main' 15mm pipe via 15mm isolation values.

 

[ShaunCorbs]

Shaun, I measured the flow rate is 5L/min at the shower cold water inlet pipe. That is BEFORE the water goes into the shower unit itself. So any effects of the shower unit and its heating method itself is irrelevant to my measurements.

What do you mean by "Kitchen tap 10lpm restricted"?
The kitchen tap is about 2 years old, and both the hot and cold taps have those flexi pipes connected to the 'main' 15mm pipe via 15mm isolation values.

ISO in the loft half shut, piped up in 10mm , flexi behind the wall piped off the cold tank ??? Need to trace every inch of the pipework

And modern taps are restricted try removing the airrator

 

[UserSteve]

More information about my setup:

The electric shower has only a cold water feed.
The cold water pipe into the shower is a 15mm pipe that is fed from a 15mm riser pipe that comes from the downstairs kitchens sink cupboard.
The riser pipe goes from the stopcock in the kitchen cupboard up to the water tanks in the loft.

 

[ShaunCorbs]

What do the tanks get lpm wise ?

 

[UserSteve]

ISO in the loft half shut, piped up in 10mm , flexi behind the wall piped off the cold tank ??? Need to trace every inch of the pipework

And modern taps are restricted try removing the airrator

Thanks for the reply, but I don't understand some of what you are saying here (I'm a complete newbie to plumbing. Biggest plumbing DIY job I've done was replacing the stopcock this morning

ISO in the loft half shut

What does this mean please? What is ISO?

piped up in 10mm

Not sure what this means. The riser pipe from the stopcock to the loft water tank is 15mm if that is what you mean?

flexi behind the wall piped off the cold tank

Not sure that this means. Which wall? The cold water inlet to the shower is fed via a 15mm copper pipe which passes thru two 90-degree 15mm copper bends, and then joins the riser pipe via a 15mm copper T connector. The total distance from the T connector to the shower unit is about 50cm.

And modern taps are restricted try removing the airrator

Ok, good to know. Lets assume mhy kitchen tap has an aerator. Would removing the aerator on my kitchen tap improve the flow rate at my electric shower cold water inlet?

 

[UserSteve]

What do the tanks get lpm wise ?

How would I go about measuring the lpm into the tanks?

The two 90-degree bends in the piping going to the shower appear to be pushfit. So perhaps I can easily disconnect one of them, measure the flow rate, and just re-connect it without any drama?

I have just done another useful measurement. I connected my 15 meter garden hose (15mm width) to the out pipe of the stopcock under the sink, and ran it up to the bathtub. The flow rate into a bucket was 16lpm (4 litres in 15 seconds). So the water pressure from the stopcock is quite capable of pushing at least 16lpm up 4 meters of height through a 15 meter length 15mm diameter hose tubing with many curves and kinks.

 

[snowhead]

Between the stopcock and kitchen sink, the water flows through two 15mm isolation valves (the standard ones with the flathead screw), and five 90-degree bends.

The standard quarter turn 15mm service valves are very restrictive especially if there is more than 1 in the same pipe run.
Replace with full bore or better still eliminate.

Flexi hoses to taps are restrictive.

But as Shaun has said, shower flows are limited due to the amount of heat they can get into the water.
What's the manufacturers spec for flow rate for your shower model?

 

[Timmy D]

Just to add to this, with a 30c temp rise, a 12kw shower won’t be able to put out more than about 5.5 LPM. It doesn’t have the power.

So even when you’ve sorted out the flow restrictions and upgraded the shower, you might only gain 1LPM.

 

[UserSteve]

So it appears my bathroom and electric shower are gravity fed from the water tanks in the loft.
The bottom of the tanks are about 100cm above the electric shower.
So a height of 1 meter means I only have about 0.1 bar of pressure for the electric shower.
The pipe from the water tank to the electric shower is 15mm.
Would there be any increase in flow rate in replacing the 15mm pipe with a 22mm pipe?
If so, what would the increase in flow rate be?

According to this flow rate calculator (Flow Rate Calculator - Pressure and Diameter | Copely - https://www.copely.com/tools/flow-rate-calculator/):
I should get about 7.8 LPM thru 15mm at 0.1bar from 1 meter
I should get about 24 LPM thru 15mm at 0.1bar from 1 meter

So it seems I could double (at least) the flow rate to the electric shower by going from 15mm top 22mm pipe.
Can anyone comment on whether this is feasible or sensible?

 

[ShaunCorbs]

Better off piping it off the mains

 

[UserSteve]

Better off piping it off the mains

How much work is involved to do that?
I am guessing that to pipe the electric shower off the mains (about 4/5 meters from downstairs to the bathroom upstairs) is a lot more work that changing the 15mm pipe from the loft tank to the bathroom outlet (about 1 meter from bathroom straight up to the loft tank directly above)

 

[Timmy D]

Tye shower should be fed from the mains, not tank.

Is the shower feed a dedicated feed from the loft tank? Or does it tee off of the bathroom feed?

I ask because you could take a mains feed off of the loft tank feed. If the shower has a dedicated feed from loft, quite easy to connect to tank feed.

If its off the bathroom feed, you could run a new feed from tank feed, along loft and punch down through ceiling to shower.

But like i said, even if you get the shower feed up to 20lpm, the shower still only has enough power to provide shower temp water at around 6lpm.

 

[Essaboy]

Sounds to me that the 15mm pipe that you are calling the riser and tee’s off to feed your shower is in fact the cold water bathroom supply coming from the tank in the loft. Go in the loft find the 15mm pipe feeding the cistern valve in the tank and tee off a new pipe to the shower from this pipe before it goes into the tank. Full mains pressure now available at your shower heater