underwhelming shower

You'd need to speak to someone who is familiar with this particular model, but in general if the primary loop temp is high enough (is it practical to get a thermometer on it to check?) but the DHW is not, then poor heat transfer does seem likely. Either scaling or a weak pump.

Depending on the location of the DHW thermistor I would expect it not to modulate down if the PCB thinks the DHW temp is too low, but at the same time it will *have* to modulate if the primary loop temp goes too high, for obvious safety reasons, so your call... At least the DHW plate is reasonably cheap, I *think* this is the right one, but you'd need to check, obviously:

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(I have used this company in the past). Don't know if that price includes the 4 seals, you'd have to check that as well :)

Obviously you have to partially drain the primary loop to remove the DHW plate, how easy that will be, will depend on where the various shut off's and drains are...

Reply to
Lee
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snip

thanks again for your help here Lee

I will call the people who service it tomorrow and pass it over to them Considering I was going to the trouble and expense of fitting an electric unit, I may come out of this ok

Cheers

Pete.

Reply to
pete.r

I was rather thinking that this means you have a spare way in the CU, making it slightly less of a job.

Reply to
newshound

The cost of fitting an electric shower depends a lot on your house layout (sometimes quite easy). One advantage it provides is an independent source of hot water if the boiler fails. More expensive to run, of course.

Reply to
newshound

Interesting - we aren't getting the expected flow rates through the combi and although reluctant to add any more infrastructure this may be an option.

However all the blurb gives me the impression that they may be bloody expensive.

As far as I can see they are more or less a very large expansion vessel such as you have on a central heating system.

Cheers

Dave R

Reply to
David

With most installations, the limitation on combi flow rate is the speed it can heat the water rather than the mains supply rate. Accumulators really only solve the problem of a mains supply with good pressure but very poor flow rate.

Probably - they are mains pressure vessels - so probably similar money to an unvented cylinder.

Yup, expansion and storage. So you can use water at a much higher rate than the mains can supply for a time. (if sized right - for as long as you need for any typical use)

Reply to
John Rumm

I think that would depend upon a few things. Other things being equal*, combi wins over stored water, which could reduce or even remove any extra running costs for the OP.

  • The *experience* of a decent flow shower. Does it make you stay under longer?!
Reply to
RJH

Picking this up again, I have done a few quick tests to confirm that it isn't the boiler running out of heat.

It shouldn't because it is a WB Greenstar 38 CDi Classic which should be able to raise 19.1 litres/min by 30C. It was sized to be able to (just) run two showers at once.

As a simple test I put the shower on running at full chat (for this shower) and then turned on the wash hand basin mixer on to hot only. Flow rate of the shower dropped but the shower stayed hot and the basin tap also yielded toasty hot water. To me this suggests that the issue is probably the total flow of water through the pipe work and not the heating capability of the boiler.

I have realised that I can't easily measure running pressure inside the house because I don't have a single "real" tap to attach a meter to - everything goes through some kind of mixer.

I can't even confidently measure full flow rate because I don't know if the mixer taps are throttling the flow.

Between the incoming mains and the house plumbing I have a pressure limiting valve (which I am waiting to remove) and a water softener.

I can bypass the water softener but I suspect the pressure limiting valve (fitted as part of the water softener install) may be throttling the water flow.

Anyway, I do seem to have a limit on the flow from the boiler to the upstairs bathroom shower.

A rule of thumb might be to add 10 minutes of higher pressure to the shower flow, so a minimum of a 190 litre capacity vessel?

Or do you have to size for say 80% of the capacity being available before the flow enhancement tails off?

Unfortunately I can't do much active investigation at the moment as I'm embroiled in lounge flooring.

Cheers

Dave R

Reply to
David

You'll probably fine the heat exchanger in the combi is limed up. May be possible to remove and descale with vinegar or similar.

If you have a softener don't neglect it. Only the ones you add salt to work. The others are snakeoil.

Reply to
harryagain

Have you read anything I have written?

Heat is not the problem.

Further:

The boiler is almost brand new. You may (in your haste to post your wonderful solution) have missed the mention of the water softener - so pray enlighten me, how does softened water "lime up" a heat exchanger?

Read a bit more?

Or post a bit less????

Reply to
David

Just looking back at this thread, I can't see any background on your specific problem here. Could you recap the main problem?

I used to have a 35kW combi, and it could just about do two showers. The mains in that place could only do about 17 lpm tops anyway.

Some combis have flow regulators and some don't. Those that do will restrict the flow to what can be heated to a resonable level. Others will allow unlimited flow (up to the pipe and supply capacity), but allow the temperature to fall should you exceed the power requirements.

Not sure what yours does. Hence the drop in flow you are seeing might be you reaching the capacity of the supply or the boilers flow regulator kicking in.

How about a washing machine / dishwasher tap?

Outside tap?

(to be fair, many of the pressure test kits you get from the plumbers merchants have an adaptor widget that lets you clamp the gauge onto a mixer tap as well)

They may well limit it a bit - depends on the size of the input pipes - many mixers that are "single hole" fixing use micro-bore pipe to feed them which will limit them a little.

You could use multiple taps and buckets for an estimate...

Perhaps - but IME if they are working right, and they are not reducing the pressure massively, they ought not have much effect on flow rate.

Do you see this when running just that shower, or that shower with other uses of water at the same time?

What about at a basin in the same room?

You would have to download and read the specs on the accumulator in question - you may not get the same performance (or even method of operation) from all of them.

Reply to
John Rumm

Well if it's brand new, get whoever installed it back to fix it. Magnetic/electronic water softeners are bollix. Only the ones you put salt in work. And if you don't put salt in, even they don't work.

Reply to
harryagain

I was tagging onto someone else reporting a disappointing shower. I had (as far as I can recall) the same shower fitting in another house with a smaller WD combi and I got a powerful shower. This one seems to be less powerful.

The mixer is Triton Unichrome Aire Thermostatic Bath/Shower Mixer with Riser Rail.

I am scouring the documentation and it says that the minimum flow rate for optimum operation is 8l/minute. I can't find what the maximum flow rate is, though. It would be nice to see maximum flow rates graphed against running pressure.

My test of hot flow and pressure drop was in the bathroom - shower and wash hand basin both on. When I have the TUIT I will take maximum flow measurements of hot and cold at various taps.

I am assuming that the maximum possible flow at a mixer shower is the maximum hot water flow plus enough cold to bring the temperature down to comfortable.

The specifications for the boiler are perhaps a little confusing as it states:

DHW specific rate - 30C rise is 19.1l.

Max DHW flow rate - 40C rise +/- 15% 14l.

So...ummm...in the Winter, if the cold water is at 5C in the mains then to raise it to 45C you should get a flow rate of roughly 14l/min of hot water. Mixed with a bit of cold to bring it down to the red button 38C that should be a fairly decent flow.

Put it another way as the boiler is rated at maximum 40kW heat output then it should be 4 * as powerful as a 10kW electric shower.

I need to do a load of tests to find maximum flow rates in various locations but at the moment I am just thinking about it as I go about my boring flooring.

Cheers

Dave R

I see also it needs 1.7 bar working pressure for maximum flow.

Reply to
David

I haven't been reading all this thread so excuse me if its been said earlier..

nobody has put one of those eco disks in the shower somewhere have they? They restrict the flow a lot to save water. The one they sent me free only had a hole in about 2-3 mm wide so it just went in the bin. My shower can put out about 25 l/min if on full with the soaker on but I seldom do that as I prefer some pressure in the jets.

Reply to
dennis

The "power" of a shower is really the multiple of the flow rate and the pressure. The higher they are, the more water hitting you per minute - the more force you will feel.

IME bar mixers tend to give slightly less flow rate than some other mixer types - but most will do a reasonable shower at around 8 lpm, and a "good" one with about 12 lpm. However you need adequate dynamic pressure to be able to get those flow rates. It may be that this house has less pressure than the last.

Indeed. You ought to get a more than adequate shower out of a boiler of that power.

Power in heating terms yes, but if the water system can't squeeze water through the shower head fast enough you simply won't be able to use all that power available from the boiler.

Note that choice of shower head can also make a big difference. It might be worth testing the flow from just the shower pipe without the head attached.

Yup, even a static pressure reading would be good to at least understand the starting point. Let's face it, if you only have 1 bar of static pressure, then any shower is likely to be a bit disappointing.

Something like:

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on a washing machine tap or an outside tap if you have one would be a good start.

Reply to
John Rumm

I have a pressure test meter in stock (somewhere) and IIRC static pressure was around 2.7 bar. Somewhere just under 3 bar anyway because that was the maximum pressure for the water softener. I think.

I know I did a rough static pressure and flow rate test before all the work was done but that is over 2 years ago now and memory is somewhat hazy.

I have adapters for old style mixer taps but they seem to rely on a (roughly) right angled outlet so you can clamp a rubber seal against the outlet by applying pressure on the back.

These fancy basin mixers are a slightly bent tube, all elegant curves and no point to apply a clamping pressure.

I'm starting to wonder if there is something unusual about the install of the bar mixer on the bath - which is leading to sods law which says I'll have a struggle getting the bath panel off for a look see. Could even be something silly like the wrong isolating valves or the isolating valves not being fully on.

Anyway, very helpful to discuss this as it helps new ideas settle in.

Cheers

Dave R

Reply to
David

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