Electric Shower Pressure Query

[Dave1UK]

Hi,

We are renting and have a electric shower downstairs (extension) - a 9.5kW Triton T80Z fast-fit electric shower as well as a combi boiler Viessmann Vitodens 100-W B1KC 35 kW. Upstairs is a standard shower/bath direct from boiler.

Our family members tend to use the downstairs electric shower and have been recently complaining about the water pressure. We are well aware that if any water outlet is being used in combination then there is a drop in pressure at both ends - for whatever reason. This has occurred at times when only the shower is being used though. I performed a approximate water pressure test using a 1L jug and a time of 6 seconds, results where when the electric shower heating element is essential off not operational i.e. cold then the pressure is 7.5L/min @ 0.75 bar. When at a reasonable temperature it is 6L/min @ 0.6 bar.

The electric shower is rated for 8L/min @ 1 bar. So I guess we are slight off?

The main query is whether there is anything that can be done to increase the water pressure, I read that due to having a combi boiler a water pump isn't possible, hence the electric shower route I'm assuming?

Also would an upgrade to the 10.5kW version with everything as is just a swap out make any difference as it's rated with a higher flow rate? I am aware that a new electric cable may need to be fed depending on the current setup however if there would be no improvement due to being bottle necked by the water pressure there wouldn't be a point.

Appreciate any help/advice.

 

[OnlQQker]

It's impossible to know your complete set up, but if you are sharing water mains with a neighbour then everything they do will also affect the pressure. This could explain why pressure drops for no reason when you're not using anything and somebody is showering.



I have fitted these before now in cases like yours and they work well. HomeBoost Mains Booster Water Pump | Salamander Pumps - https://www.salamanderpumps.co.uk/products/mainsbooster/homeboost/#compatibility

 

[Pretty Mouth]

Your water pressure probably isn't the problem here.

(Assuming you are always using the high setting rather than economy) the shower element heats at a set output, this doesn't change. When you turn the dial to adjust the temperature, you adjust the flow rate of water: the slower the water passes over the element, the more heat it absorbs, and so the warmer it will be when it leaves the unit.

So a particular water temperature should always have a corresponding flow rate (all other things being equal. For example, in winter the water entering the unit will be cooler, so would need to spend more time with the element to heat up to that particular temperature).

I assume you're using the shower on the high setting rather than economy? It may be that one of the elements has died, so it's not heating the water fast enough, and you have to lower the flow rate to compensate.

Alternatively, it may just not be living up to expectations, and maybe a 10.8kW shower would be better.

 

[Darkwood]

The regulator in the shower could be on its way out too, (the temp dial), not common but agree with other suggestion that common water supply or you're close to industrial or commercial with regular demand that could drop pressure, this would result in the shower getting hotter yet less water output.

 

[Bob Geldoff1234]

Is the cold tap pressure ok in the bathroom where the shower is? Where the shower connects to the cold water pipe there is often a filter in the incoming tube.If grit from the water starts to clog up the filter then the water pressure will reduce.Might be worth checking the filter(if there is one).

 

[pirate]

One query I have here is why, when you have a combi boiler, do you have an electric shower downstairs?
Most combi boilers,in my experience, output enough pressure for a shower of the normal type having hot and cold inputs.
A purely electric shower is useful in case the boiler fails, or if it's tricky to plumb it in to hot and cold supply, but that is unusual. Assuming the pressure is fine at the main bathroom, I suspect it's a low cold water pressure overall that is the problem. I say this because the OP suggests it is the flow rate that is the problem, not the temperature. There are other solutions if the flow rate is the only problem.

 

[Dave1UK]

It's impossible to know your complete set up, but if you are sharing water mains with a neighbour then everything they do will also affect the pressure. This could explain why pressure drops for no reason when you're not using anything and somebody is showering.



I have fitted these before now in cases like yours and they work well. HomeBoost Mains Booster Water Pump | Salamander Pumps - https://www.salamanderpumps.co.uk/products/mainsbooster/homeboost/#compatibility

I don't believe we are sharing water mains with a neighbour, we have our own water meter in our front drive. It's a mid-terrace property.

Just had a look at the link, why do companies (Viessmann) state combi boilers aren't compatible with water pumps yet this states it's compatible with a combi boiler? I will do a check on our other taps and upstairs shower in terms of flow rate, as it is generally "stronger" than the electric shower. As this unit is fit essentially directly onto the boiler there may be little to no benefit of the boost of advertised (12L/min) if the house is already getting close to that but the electric shower being an isolated case if that makes sense.

Your water pressure probably isn't the problem here.

(Assuming you are always using the high setting rather than economy) the shower element heats at a set output, this doesn't change. When you turn the dial to adjust the temperature, you adjust the flow rate of water: the slower the water passes over the element, the more heat it absorbs, and so the warmer it will be when it leaves the unit.

So a particular water temperature should always have a corresponding flow rate (all other things being equal. For example, in winter the water entering the unit will be cooler, so would need to spend more time with the element to heat up to that particular temperature).

I assume you're using the shower on the high setting rather than economy? It may be that one of the elements has died, so it's not heating the water fast enough, and you have to lower the flow rate to compensate.

Alternatively, it may just not be living up to expectations, and maybe a 10.8kW shower would be better.

Yes shower is generally being used on high setting mode instead of economy mode however even on high setting mode the temperature dial would only be set to about 50% as 100% is almost kettle temperature. Aware the hotter you put it the slower the water trickles through. However was wondering whether as on cold we are only getting 0.75 bar whether there are gains of 0.25 being lost somewhere/make much of an improvement? As on cold no heating elements are used therefore no bottleneck, should be a straight flow through.

I will have a go and experiment with the settings again, good point about a potential heating element being bust, would there be a way to test this? I believe the unit is dated 02/14, most likely manufactured date however it most likely is 3-4 years old now?

The regulator in the shower could be on its way out too, (the temp dial), not common but agree with other suggestion that common water supply or you're close to industrial or commercial with regular demand that could drop pressure, this would result in the shower getting hotter yet less water output.

Is there a way to test this/isolate the problem?

Is the cold tap pressure ok in the bathroom where the shower is? Where the shower connects to the cold water pipe there is often a filter in the incoming tube.If grit from the water starts to clog up the filter then the water pressure will reduce.Might be worth checking the filter(if there is one).

We have a sink in that bathroom and the flow is the same as elsewhere in the house. Just the shower being an isolated issue. However will check flow rates on all the taps just to get an idea. Will also check your filter suggestion as not sure whether one is present will check in the manual.

One query I have here is why, when you have a combi boiler, do you have an electric shower downstairs?
Most combi boilers,in my experience, output enough pressure for a shower of the normal type having hot and cold inputs.
A purely electric shower is useful in case the boiler fails, or if it's tricky to plumb it in to hot and cold supply, but that is unusual. Assuming the pressure is fine at the main bathroom, I suspect it's a low cold water pressure overall that is the problem. I say this because the OP suggests it is the flow rate that is the problem, not the temperature. There are other solutions if the flow rate is the only problem.

According to some research prior to posting here it is quite common practice for a second bathroom (no clue why just what I read)? We have an upstairs main shower regulated by the boiler. The house had an extension whereby for the 2nd bathroom now a electric shower was installed. The boiler itself is situated literally 4m from the electric shower (small utility room next door) so running pipes would have been easy.

Judging by the extension workmanship lets just say a lot to be desired, I wouldn't be surprised if everything was just done on the cheap and ASAP.

 

[brianmoooore]

Looking back at your original post, you say there have been complaints about "water pressure". I don't quite understand what this means.
Do they mean that the water flow rate is insufficient at a normal showering temperature? If so, this is nothing to do with water pressure, and is the result of a faulty shower, an incorrect shower head having been fitted, or unrealistic expectations of electric showers.

 

[Dave1UK]

Looking back at your original post, you say there have been complaints about "water pressure". I don't quite understand what this means.
Do they mean that the water flow rate is insufficient at a normal showering temperature? If so, this is nothing to do with water pressure, and is the result of a faulty shower, an incorrect shower head having been fitted, or unrealistic expectations of electric showers.

Yes the flow rate being lower on normal showering temperature. The advertised specs for electric showers what sort of temperature range are they based on (asking as nothing seems to be specified anywhere)? i.e. 8l/min @ 1bar for a 9.5kW, if that's the output on cold water sure (in our case), but on the max it would be half that even less if that makes sense.

 

[DefyG]

Is scale a problem where you live (ie hard water). De-scaling the unit/hose and head can often make it seem like new!

 

[Pretty Mouth]

Yes shower is generally being used on high setting mode instead of economy mode however even on high setting mode the temperature dial would only be set to about 50% as 100% is almost kettle temperature. Aware the hotter you put it the slower the water trickles through. However was wondering whether as on cold we are only getting 0.75 bar whether there are gains of 0.25 being lost somewhere/make much of an improvement? As on cold no heating elements are used therefore no bottleneck, should be a straight flow through.

I will have a go and experiment with the settings again, good point about a potential heating element being bust, would there be a way to test this? I believe the unit is dated 02/14, most likely manufactured date however it most likely is 3-4 years old now?

The only thing I can think of is run it on high setting, then change down to economy setting and see if there is any difference in the water temperature.

If no difference in temp, then I'd expect an element has gone completely. If it runs cold, without any heat at all in economy, then I'd also expect an element to have gone. If it is noticably cooler in economy setting, but there is some heat, then I'd expect the elements to be working as they should be.

 

[brianmoooore]

Electric showers follow a simple equation: Power input = flow rate x temperature.
Rearranging, temperature = power input/flow rate, so, if the temperature is correct and the flow rate is low, the power input must be low as well.

The only thing I can think of is run it on high setting, then change down to economy setting and see if there is any difference in the water temperature.

If no difference in temp, then I'd expect an element has gone completely. If it runs cold, without any heat at all in economy, then I'd also expect an element to have gone. If it is noticably cooler in economy setting, but there is some heat, then I'd expect the elements to be working as they should be.

 

[Avo Mk8]

As above, the flow and temperature you get from an electric shower is determined by the laws of physics.
Mira published the graph below to illustrate the performance of their showers.
(from this publication: https://www.mirashowers.co.uk/media/1453/miras-guide-to-electric-showers.pdf)

Assuming cold water is coming into the house at say 15 degrees, and you like a nice toasty shower to be at 40 degrees, you need the shower to heat the flow of water by 25 degrees.
The graph indicates that to achieve a flow of 6l/min, you need at least a 9.6kW shower element.

The original post #1 suggested the shower is rated at 8l/min at 1 bar. That may be the max flow you can get out, but the rise in water temp you would get from a 9.8kW shower would be about 18 degrees, so would feel cool! If you then compensate by turning the shower temperature up (which just reduces the flow) you would be down to about 6l/min to get a comfortable temperature.

From the OP's observations I am wondering if the shower is actually performing more or less consistently with the graph below?
If so, maybe the conclusion is that a more powerful shower would improve everyone's showering experience!

 

[brianmoooore]

Pretty Mouth's tests that I quoted above will determine if both elements are working, and if they are, it's likely that the problem is just unreasonable expectations.
I've also had the odd complaint of poor electric power flow which turned out to be tht the supplied shower head had been replaced by one intended for showers fed from a hot water system. Electric showers give the illusion of flow by using very fine jets in the head. If this is replaced by a head with larger jets, you get to see how poor the flow really is.

 

[Dave1UK]

Is scale a problem where you live (ie hard water). De-scaling the unit/hose and head can often make it seem like new!

Yes we do have a bit of a scale problem but nothing serious. Yesterday I took the unit apart, and checked the piping also the filter and they are spanking clean, 0 signs of any scale. When initially performing the flow test I tested it with the shower hose and head and also without i.e. just directly from the electric shower itself just to try and rule out any bottle necks with the hose/head.

The only thing I can think of is run it on high setting, then change down to economy setting and see if there is any difference in the water temperature.

If no difference in temp, then I'd expect an element has gone completely. If it runs cold, without any heat at all in economy, then I'd also expect an element to have gone. If it is noticably cooler in economy setting, but there is some heat, then I'd expect the elements to be working as they should be.

Tested this yesterday, put it on economy mode and about 80% temp turn and that's a reasonable heat although very poor flow rate in comparison to max/high mode and about 60% temp turn for a bit of a hotter heat.

As above, the flow and temperature you get from an electric shower is determined by the laws of physics.
Mira published the graph below to illustrate the performance of their showers.
(from this publication: https://www.mirashowers.co.uk/media/1453/miras-guide-to-electric-showers.pdf)

Assuming cold water is coming into the house at say 15 degrees, and you like a nice toasty shower to be at 40 degrees, you need the shower to heat the flow of water by 25 degrees.
The graph indicates that to achieve a flow of 6l/min, you need at least a 9.6kW shower element.

The original post #1 suggested the shower is rated at 8l/min at 1 bar. That may be the max flow you can get out, but the rise in water temp you would get from a 9.8kW shower would be about 18 degrees, so would feel cool! If you then compensate by turning the shower temperature up (which just reduces the flow) you would be down to about 6l/min to get a comfortable temperature.

From the OP's observations I am wondering if the shower is actually performing more or less consistently with the graph below?
If so, maybe the conclusion is that a more powerful shower would improve everyone's showering experience!

View attachment 109616

Will take a look at the link and graph appreciated.

Pretty Mouth's tests that I quoted above will determine if both elements are working, and if they are, it's likely that the problem is just unreasonable expectations.
I've also had the odd complaint of poor electric power flow which turned out to be tht the supplied shower head had been replaced by one intended for showers fed from a hot water system. Electric showers give the illusion of flow by using very fine jets in the head. If this is replaced by a head with larger jets, you get to see how poor the flow really is.

I personally rarely use the electric shower downstairs but have previously and to me it worked fine. However after the complaints from family members thought I'd investigate.

________________________________________________________________________________________________________________________________

To add I wanted to check the whole setup and cabling. So I did yesterday and to me it seems like a possible cowboy installation? As trying to figure if installing a higher kW unit would be possible but it wouldn't with the current cabling. I'm dubious if even the current setup is appropriate and not currently overloaded!

So we have the 9.5kW electric shower which is using a 6mm cable connected approximately 1.5m through the wall going to a isolating switch outside the bathroom (switch between the electric shower and mainboard power panel). This then feeds through the kitchen going to the utility room just outside under the stairs into the mainboard this is approximately a further 5.5m so total of 7-8m of cable. It's fused to a Crabtree B32 61 MCB breaker (rated 32A?).

The 9.5kW unit according to the manufacturers spec should have a 40A breaker? Heck even the 8.5kW needs a 40A unless I'm not understanding something along the lines. The 7.0kW/7.5kW would of been fine for the 32A and 6mm cable.

I have also read conflicting views elsewhere whether a 6mm cable under a certain total length is suitable as a replacement for a 10mm under certain conditions?

So now I'm wondering whether enough power is even being delivered to the unit to operate at it's full potential? Or would the unit not operate at all otherwise?