About to buy a new house that needs a bit of modernisation work. The house has a standard bolier/hot water tank set up (ie, not a combi high pressure system)

First up are the bathrooms – I thought I would be fitting power showers but the plumber has suggested a pressurised hot water tank – he says we can then just use thermostatic shower heads and we’ll still get showers similar to a power shower.

So – are they any good? And experiences?

Depends on the water pressure to the house. My understanding is that these basically work off mains pressure for both hot and cold water. If you’ve got good mains pressure you’ll get good hot water, if poor , poor.

Pumps for showers are noisy, expensive, and fairly unreliable – pressurised hot water a far better solution if you can get it to work.

Yes and what he said.
Don’t get a Megaflow even though they are market leader (read expensive) as the internal bubble/baffle arrangement needs recharging at least annually. Simple task but nobody ever does it. The cheaper units with separate expansion vessel are better IMO.

It’s the French standard so I have them in all my properties. I can’t think of any disadvantages but a few advantages:

The water is never exposed to the atmosphere (or dead rats etc.), there’s no ball valve to leak or overflow to flood the place, all the mixer taps work fine and showers run at mains pressure, it’s easier to run the solar hot tank and the normal hot tank in series when the solar tank isn’t warm enough.

We had one in a fairly new build house.
It’s like an ‘inside out’ hot water tank – i.e the tank stores hot water, but the ‘useable’ water passes through it to heat that up.

It was very good I found, as you never ran out of hot water, it was mains pressured and could run all three showers without any noticeable loss of pressure, and you can drink the hot water/use it for cooking, as it’s not been stored in a tank.

The downside – not every plumber can fix them when they break, and they are pricey to fix when this happens….

DrP

Similar situation for us. Our plumber has said a modern combi will have a high enough flow rate to be good for up to 3 bathrooms (inbound supply dependant).

Might be worth a look as either combi or presurised tank are dependant on the flow to the house and with a combi you don’t have a tank to worry about and have unlimited hot water as well.

Our water pressure is rubbish so we had a pump fitted

my mum had one installed – excellent, but they live near the water tower and pressure mains pressure is fab..

did free up space though by consolidating the hot and cold tanks

Some great responses so far – really thank you all.

The reasons I am considering one are:

– Free up space in the main bathroom.
– After living with a combi boiler for the last 13 years I don’t want another (even when flow is at its best it isn’t ‘like a power shower’, despite it being a very new one (had a Worcester Bosch fitted 4 years ago).
– The new house has recently fitted WB traditional boiler so seems a shame to rip it out.
– Got two young girls so, with the future in mind, I want a system that the whole family can use at the same time.

I guess I need to monitor water pressure at the new house though – it is detached and on a 1980s development so I *assume* it will have a dedicated feed (unlike our current house that shares with 5 other properties!)

We have one, powers two good showers no problems(both can run together in the morning). We do have very strong water pressure.

You need to measure pressure AND flow.
Low flow can be overcome a lot easier than low pressure

– After living with a combi boiler for the last 13 years I don’t want another (even when flow is at its best it isn’t ‘like a power shower’, despite it being a very new one (had a Worcester Bosch fitted 4 years ago).

I’m not a plumber so someone may correct me but as I understand it…

If your boiler is correctly sized then the presure/flow rate from a combi boiler will be the same as can be achived with a presurised hot water tank. i.e. mains presure/flow rate.

So if the showers from the combi wern’t to you liking the presurised system won’t be any better. Its not like the presurised system has a pump to increase the presure in the tank. So if you want the full pressure washer style shower effect you may be better sticking with the traditional system and adding pumps to each of the showers.

jfletch – this is exactly what i need to know…

So if the showers from the combi wern’t to you liking the presurised system won’t be any better. Its not like the presurised system has a pump to increase the presure in the tank. So if you want the full pressure washer style shower effect you may be better sticking with the traditional system and adding pumps to each of the showers.

Not correct, a pressurized tank will have a better flow rate than any combi.

Edit; If there is a decent incoming pressure/flow rate.

If there is a decent incoming pressure/flow rate.

I guess I need to check this when we move in (and I assume I can get the plumber to do checks too)

Their are 2 main advantages to a pressurised hot water tank over a combi boiler.

1. You have a large tank of water heated to a certain temperature also at mains pressure to feed into a shower this will remain constant all year around. A combi boiler has an ability to raise the temperature of the incoming mains water by a certain amount for a certain flow rate this tends to mean that with a correctly specified combi boiler you can have a nice powerfull hot shower in summer but in winter when the mains water can be as low as a few degrees your shower is either cooler or less powerfull.

2. The second point is that a combi boiler can react badly to sudden alterations in the demand for hot water so another tap being turned on can affect the amount of hot water going to the shower causing a spike in temperature either up or down.

I would dispute that if you are unhappy with a combi boiler run shower that you will also be unhappy with a pressurised shower. Their is a lot more to a good shower than just the boiler. From our experience a pressurised hot water system properly fitted with a decent supply of main water through simple unrestricted large bore pipe work is far superior to a combi boiler.

If your boiler is correctly sized then the presure/flow rate from a combi boiler will be the same as can be achived with a presurised hot water tank. i.e. mains presure/flow rate.

Even if this was correct (which I’m unsure of) but I doubt a combi could produce enough hot water for two showers simultaneously.

Also remember that you can have the best pressure/flow but if the pipework to the showers is too small diameter you’ll not get the full benefit.

I had a Megaflo installed 8 years ago and it’s great. You need to regenerate the air gap at the top of the tank occasionally but this only requires that you hold a valve open by hand and is done in less than 5 mins.

I fitted a thermal heatstore recently.

I had the supply pipe from the edge of the property upgraded to handle it.

Infinitely better than my experiences of a combi boiler.

We have had unvented systems installed at our last two places. Bloody excellent if you have sufficient pressure.

Ours is a Megaflo too – recharging them is very easy. You’re supposed to get them serviced annually but TBH, that’s the main component of it, and you can do it yourself in five mins.

Not correct, a pressurized tank will have a better flow rate than any combi.

My plumber is giving different advice. So please explain how a tank at mains presure can have a better flow rate than the mains themselves?

Surley the presure/flow can only be as good as the supply into the tank, its not like you can empty the tank faster than it fills as its a sealed system, hence why you can’t have a pump.

This however does make sense

Their are 2 main advantages to a pressurised hot water tank over a combi boiler.

1. You have a large tank of water heated to a certain temperature also at mains pressure to feed into a shower this will remain constant all year around. A combi boiler has an ability to raise the temperature of the incoming mains water by a certain amount for a certain flow rate this tends to mean that with a correctly specified combi boiler you can have a nice powerfull hot shower in summer but in winter when the mains water can be as low as a few degrees your shower is either cooler or less powerfull.

2. The second point is that a combi boiler can react badly to sudden alterations in the demand for hot water so another tap being turned on can affect the amount of hot water going to the shower causing a spike in temperature either up or down.

I would dispute that if you are unhappy with a combi boiler run shower that you will also be unhappy with a pressurised shower. Their is a lot more to a good shower than just the boiler.

This makes more sense to me but having a combi in the current place I can’t say I’ve experienced these issues. A thermostatic shower solves the winter/summer temperature issues and if the flow rate is less in the winter its impeceivable. The only issue with the combi is the supply to the house being crap but that would also affect a presurised system.

My plumber is giving different advice. So please explain how a tank at mains presure can have a better flow rate than the mains themselves?

Surley the presure/flow can only be as good as the supply into the tank, its not like you can empty the tank faster than it fills as its a sealed system, hence why you can’t have a pump.

For starts the pressurized cylinder will have a 22mm inlet and 22mm outlet (more flow). There’s a few other reasons which i cant be arsed to explain, you need to understand the difference between flow rate and pressure.

18 years experience tells me a pressurized cylinder is way better in every aspect than a combi.

Run two taps on a combi system and two taps on a pressurized cylinder and you can see the difference.

So Mr Bean – assuming good water pressure to the house, is a pressurised system going to give us a ‘power shower’ experience? We are looking to install a walk-in shower with a big head something like this

http://www.bathstore.com/products/cloud-300-brass-round-single-function-fixed-shower-head-with-300-wall-arm-2976.html

Would it give us a good ‘drench’ experience?

assuming good water pressure to the house

Flow is as important as pressure (as is all the pipework to/from the cylinder. AFAIK you’re never going to get a power shower experience with a large headed shower unless you live under Niagra Falls.

Okay, so I need good flow and pressure. FWIW, the house is almost at the same level as the water tower and the house we now live in (pretty much on the other side of the street) gets decent flow even though it is the last in a line of six houses on a shared feed using very old lead pipework. The new house should have a much better supply given that it is a 1980s build.

johndoh, a megaflo or equivalent will give you the best shower. In my experience these ‘deluge’ showerheads are not that great from a combi.

Well I won’t be using a combi – my consideration is a pressured HWT against pumps.

You are forgetting one of the big bonuses of a mains cylinder over combi.

Back up hot water supply if the boiler goes wrong as you can heat with an immersion heater, or the right cylinder could have solar added too (I know you can add solar to boilers too before it is pointed out).

If you want really good flow with multiple outlets look at accumulators. And can I recommend Oso as an alternative to all the Megaflo fans. If more of a budget then look at Gledhill.

We had one fitted a couple of years ago…it’s ace. No pump noise, loads of flow for showers and baths and a lot cheaper to run than the old boiler. Can’t find any downsides (so far).

We’ve had an Ozo unvented cylinder for 15 years now, works really well. The cylinder is 2 floors below the shower.

I would suggest you get it all designed & installed by a thinking plumber anyway.

I would suggest you get it all designed & installed by a thinking plumber anyway.

Hopefully that is what he is – the idea came from him based on listening to our requirements.

I have gone from 3 bar shower pump and gravity fed hw to a santon premier plus in my own home, far better shower and i don’t run out of hw like i did with the pump. I also have a deluge head and a 22mm thermostatic mixer shower, which was an improvement in flow over the 15mm mira valve which was in before.

I will possibly be changing to a thermal store in the future, once i get some feedback from the few that i have installed.

And yes, oso are great, way cheaper than a megaflo. In fact, i can’t remember the last time i installed a megaflo.

We have a Megaflo system and it copes with 3 showers running at the same time, they all have deluge heads, no problems at all.

What’s this about recharging Megaflow every 12 months? Ours is 3 years old and it doesn’t seem to perform any differently to when it was new.

mtbmaff, it’s just random, some can go years without needing recharged some can go less. a tell tale sign is water constantly dripping at the tundish from the prv or tprv.

Thanks supremebean for your reply, what’s the tundish? Prv, pressure relief valve?

Yes, pressure relief valve, or tprv temperature pressure relief valve.

Tundish is the black bit with gaps which is connected to the tprv. 15mm pipe in the top 22mm coming out bottom. Tprv is a brass fitting usually sited about 3/4 way up the tank and has a lever or a red knob attached.

When recharging, all you have to do is switch water main off and open lever on tprv till the gurgling stops, then turn water back on.

Ah yes! It has the instructions written on the front 😀 thanks again for taking time to explain.

For starts the pressurized cylinder will have a 22mm inlet and 22mm outlet (more flow). There’s a few other reasons which i cant be arsed to explain, you need to understand the difference between flow rate and pressure.

18 years experience tells me a pressurized cylinder is way better in every aspect than a combi.

Run two taps on a combi system and two taps on a pressurized cylinder and you can see the difference.

I understand the difference between flow rate and pressure thanks.

What I don’t know is the differences of how the flow into the house manifests its self as flow out of a shower head for the two different systems. Just the basic you get from the boiler manufacturers sites, such as “combi and pressurised systems both give mains pressure hot water”. Hence my comments before.

So are you saying that the pipe out of a pressurised cylinder can be bigger than the pipe out of a combi boiler? Therefore giving a better flow rate. What happens when the hot water is used since the boiler can’t fill it back up with hot water as fast as it is being used?

Not being arguemenative, just want to understand how it works so I can have this discussion with my plumber in a couple of weeks when he recommends me a massive combi!

Read the flow rate from a combi boiler – industry standard is 9 litres / min at 35 deg C rise.

Most are higher these days but still only around 10 or 12 l/min, unless you are on a big combi.

The boiler regulates the flow with a restrictor in the inlet normally.

Spread 10 l/min across two showers and reduced flow.
also incoming main at 8 deg in winter or lower then to achieve a decent temp you need to shut the flow down even more.

Unvented cylinders do not suffer from the same restrictions of flow, they may go through a pressure reducing valve, but when heated the pressure increases anyhow.

Doesn’t need to fill it up as it is not an instantaneous heated but has a store, modern cylinders re-heat very quickly too.

Did a bit more reading and now I understand where the difference comes. (The combi boiler heats the water that comes out of your shower, but in the pressurised system the boiler heats some water, that heats the water that comes out of your tap via a heat exchanger)

So some questions for the plumber then!

But what flow rate do you actually need for two simultaneous showers?

Our plumber is saying a 16l/min 35 deg C rise combi is fine.

I was happy before and I’m still sure it would be OK if it wasn’t for the wife’s penchant for very hot showers meaning that we wouldn’t get the desired flow rate. We don’t experience these limitations in our current house with one shower despite a very low spec combi becuase the flow into the house is the limiting factor, its so crappy the combi can heat all the water coming into the house to any temperature we want.

TBH I’d prefer the pressurised system but the isn’t a hope in hell the wife will listen to me over a qualified tradesman, unless I can convince her that she may end up with a luke warm shower!

We have a Pressurised hot water tank & reasonable mains pressure. It will supply enough water for 2 showers (at the same time) easily & fill a bath very quickly. Also the temperature of out hot water is not enough to scold, which I see as a good thing. I cannot recomend it enough.