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Original poster

Is there a combi boiler that can give water for two showers at once?

34 replies

snowgirl1 · 09/05/2014 15:01

We're looking at replacing our boiler before we start on a kitchen re-fit. I've had two central heating engineers out. Told both that we'd like a boiler that can deal with two showers at the same time. First guy has given a quote for a Worcester Bosch 42 CDi; the second guy has said that there isn't a combi boiler on the market that can really deal with water for two showers at once - you will get reduced temperature. Second guy is recommending a Megaflow.

Does anyone know whether the Worcester Bosch 42 CDi (or any other combi) would cope with two simultaneous showers?

If it makes any difference the second guy measured our water flow and said it was AMAZING. He actually stopped before turning the tap to max as it said there was no point - the flow was good enough for whichever option we went for.

OP posts:

Blu · 09/05/2014 15:08

Don't know, but will watch with interest, as our shower off a combi boiler goes off or cold if any other tap in the house is running. Can't shower whil eh washing mmachine or dishwasher is on, or if someone has flushed the toilet

sauvignonblacks · 09/05/2014 15:15

Combi boilers heat cold water on demand I.e if you're in shower and DP runs the tap in the kitchen you will lose your temperature. You can overcome this by using a thermostatic shower valve. This regulates the temperature to the shower.
I'd be more worried about the water pressure turning in a trickle. Perhaps an electric shower with a pump might help

Original poster

snowgirl1 · 09/05/2014 15:20

First guy advised that you can't have a pump with a combi. We have a shower with a pump and he advised that it would need to come out .

I know combi boilers heat water on demand, but thought that if you had a larger capacity combi boiler it would be able to heat more water therefore heat enough water for two simultaneous showers.

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sauvignonblacks · 09/05/2014 15:29

You can't pump a combi this is true but some electric showers aqualisa I think pump themselves

Original poster

snowgirl1 · 09/05/2014 15:35

sauvignonblacks you sound like you know what you're talking about. Can I ask you a question? Am I correct in understanding that the combi system is pressurised (ie. could cause inadequate old pipes that aren't up to the pressure to leak) and with a 'normal' boiler and megaflow, the entire system isn't pressurised, but the hot water tank cylinder is pressurised? We have concrete floors on the ground floor, so not too keen on the idea of a system which may cause leaks in pipes that are in the concrete...

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TeenageMutantNinjaTurtle · 09/05/2014 15:35

We just had our boiler replaced and were basically told we couldn't have a combi with 2 simultaneous showers. We have an Eco boiler, a 200ltr tank with mega flow and excellent mains pressure and we're still limited to 1 shower at a time...

sauvignonblacks · 09/05/2014 15:44

snowgirl1 you flatterer!
My understanding is combis work on mains pressure only and that is limited to 3bar in the UK but can be anything from gravity 0.1 bar upwards
Your pipe work will be either 1/2" or 3/4" the smaller the pipe work requires more pressure to increases the flow rate

Original poster

snowgirl1 · 09/05/2014 15:48

Thanks sauvignon

Teenage that's interesting - I'm not sure what the advantage of a megaflow is then... It's making me want to just stick with a 'standard' boiler and hot water tank - at least I kind of know what the deal is with that set up as it's what we've currently got; plus it's cheaper than combi or megaflow.

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ManWithNoName · 09/05/2014 15:58

We just fitted at Worcester Bosh 42 CDi (floor standing version).

We have a hot water tank and then we have a pump shower running off that. It is an old house and we wanted to be able to run a bath tap and a shower and a kitchen tap all at the same time with no pressure drop.

Our heating engineer fits factory systems and he said if you have a big enough tank and pump showers and a big enough boiler like a 42 CDi the tank plus the boiler should have the capacity to keep multiple outlets going.

Our system works just fine.

beaufontboy · 09/05/2014 23:13

rule of thumb for combi is that they only do one outlet at a time, if you were looking to have a shower and do the washing up then I would be looking a system boiler with tank. A Combi is convenient as they are on demand but the boiler suffers and it does shorten its life but you don't need a tank ! I would have a system boiler in a larger house/family situation

Swanhildapirouetting · 09/05/2014 23:34

We have the Worcester Bosch model combi (for last 8 years?)and a megaflow, and it only does one shower or outlet at a time. I always thought it was to do with the water pressure rather than the combi as the cold water is the same - ie if you run the cold water tap to brush your teeth you cannot run the shower too.
Houses in our street alter the diameter of the pipe feeding the house, as the original pipes were never designed to cope with so many outlets running at once. (Edwardians were more restrained!)

What we do is, never flush loo if someone is having a shower, run a bath for one person, then run the shower (so two people can wash at same time if necessary)

Our showers are all thermostatically controlled too, and very high pressure (but no pump that I know of (ie not electrically connected)

ouryve · 09/05/2014 23:40

I knew someone who had 2 bathrooms who had their heating system overhauled and they had a system with a combi and a tank installed. Even a high output combi can't maintain the pressure for 2 outlets at once.

springlamb · 09/05/2014 23:47

I think it is a combination of the mains pressure and how many litres per minute the combi can actually heat. I suspect trying to run 2 showers direct from a combi (and of course, you can't have a pumped shower) could be very dangerous - a sudden division if the mains pressure when you turn on another cold water appliance could end up with very hot water only in the first shower.
I used to get around this by having a thermostatic electric shower for one of ours.
The system we inherited when we moved last year is strange. There is an upstairs immersion and a downstairs immersion and the boiler only controls the heating. We have good water pressure and we can use both showers at the same time. Due to have a third shower out in shortly, but that will be an electric one.

PigletJohn · 10/05/2014 08:16

Snowgirl has a very good but undefined flow. If she has room and funds for a Megaflo or other pressurised cylinder, it will give better HW than a combi, and will be more reliable.

In most houses, the constraining factor will be the amount of water (flow, measured in litres per minute), delivered to the house from the water main. Usually this is limited by the size of the pipe between the pavement and the boiler. Very often you can greatly improve things by digging a trench and laying a new, larger one. This can be more or less difficult or expensive depending on distance and how much concrete is in the way. Older houses traditionally have small pipes and low flow.

Usually, a combi is fine if there is only one person in the home at a time running a shower or bath, and increasingly less fine as the number of users increases.

The traditional cold water tank in the loft has the purpose of allowing the flow of water from all the taps in the house at any one time to exceed the flow of water delivered to the house at any one time from the water main.

ManWithNoName · 10/05/2014 10:01

Piglet - your advice is very similar to the choices were facing.

In a large tall old house with a conventional hot water tank and an old fashioned boiler and cold water tanks up in the attic were told we could either:

a) rip everything out and install a combi and a large megaflow tank next to the boiler with a sealed system and run the showers off mains pressure; or

b) keep everything in but buy the biggest conventional oversized condensing boiler we could find to refill the hot water tank almost as fast as it drains and then install pumped showers.

We chose option b) especially as ripping out the old system was a job we could not contemplate in a listed building.

If I had a modern house I would have chosen option a) every time.

ManWithNoName · 10/05/2014 10:05

In fact we installed an extra electric shower at the far end of the house to ease the load on the boiler and because water travelling a long distance would have cooled too much before reaching a conventional shower.

The electric shower is 10.5 kW and powerful so is also a handy back up if the boiler fails as it runs straight of the cold mains feed which comes into the house just a few metres away.

shobby · 10/05/2014 10:19

We had our bathroom completely gutted in December, and went from a pathetic electric shower to a fab combi boiler powered one, and the flow and difference in amazing, miles better. We were told if we wanted another shower in the house it would have to be an electric one, no option. I'm not sure why that was though, we had a new combi boiler 2 years ago and live in a 1929 3 bed semi.

Original poster

snowgirl1 · 12/05/2014 12:33

Thanks everyone for your feedback. I think I have officially gone off the idea of a combi boiler!

Another couple of questions, if you don't mind...

if we go for a bog standard boiler can we add a megaflow (or equivalent) at a later date?

can anyone recommend a good (and aesthetically pleasing!) electric shower (thinking of electric for the 2nd shower now)

OP posts:

PigletJohn · 12/05/2014 14:00

yes

PigletJohn · 12/05/2014 14:02

(but if you don't have a Megaflo, you will need at least an ordinary cylinder. If for some reason you need to buy or change your cylinder, consider getting one that can be pressurised later.

Original poster

snowgirl1 · 12/05/2014 15:27

Thank you PigletJohn!

I was thinking that we could keep our current cylinder and maybe upgrade to Megaflo at a later date.

Another question (sorry!), as you seem to know your stuff, are there any boiler makes you'd recommend or suggest avoiding?

OP posts:

ManWithNoName · 12/05/2014 15:36

snowgirl - we had this SPORT 10.8KW&section=Electric showers&resultPageKey=152403053-0&category= Mira Sport electric shower fitted.

It works, its hot, its powerful and it doesn't look weird.

ManWithNoName · 12/05/2014 15:39

Sorry that link doesn't work for some reason.

Anyway its a Mira Sport 10.8 kw. Google to find the Mira page.

Original poster

snowgirl1 · 12/05/2014 15:42

Thanks ManWithNoName

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Deux · 12/05/2014 16:02

Have you considered installing a smaller combi boiler just for your main shower? It was something that was suggested to us but we didn't do it in the end.

The previous occupants of this house had removed the cold water feed system and it would have been a major job to reinstate it.

We have a Worcester Bosch combi, fitted last year, don't remember the model. We did an experiment where we ran both showers together, both are thermostatic, and amazingly both delivered but at a reduced flow. That said, even with the reduced flow, they were better than any electric shower I've been in.

In practice we haven't had a showering clash yet.

If a loo is flushed or another outlet used there is a reduced flow, but not temperature, but it is minimal. The toilet cisterns are fast fill ones which helps.

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