Bloke tells me “There’s no combi Boiler in the world that’ll let you run the bath AND a shower.

Brian_Pamo

Hi all

I’m guessing that we have a problem that millions of families have. We are a family of 7 and are all working. That means we all need the shower/bath at similar times in the morning. However, we’ve all been there. While I’m running the bath the shower goes weak. So, I asked Bloke down the pub which boiler we should upgrade to to get round this. I tried to tell him the make of our boiler but he simply said “It wouldn’t mater what domestic combi you have. You just can’t do it. The only way you can do this is a pressurised system”. Therefore, can anybody advise me further? What do we need to look at? If a pressurised system is the answer is that how we heat the house? What happens to the existing combi? 

Any starting advice would be appreciated please. 

Murmansk

I think he is probably correct that a combi can't do it. When he says a pressurised  system it means you have non-combi boiler ie one that just heats, gently, water for the central heating AND water for the hot taps; the hot water is stored in a cylinder rather like the one a lot of people get ripped out to have a combi boiler.

As I understand it, the cylinder in a pressurised system contains hot water that is under roughly the same pressure as mains water, this means it can potentially give a good flow of hot water to your bath, shower etc but a power shower might drain the cylinder quite quickly, depending how big it is. You'd need to wait for the boiler to heat up some more water were that to happen.

grumbler

https://www.worcester-bosch.co.uk/products/boilers/explained - see the picture in the middle.

An electric shower is usually suggested as a much cheaper option that also doesn't need extra space for the cylinder.

daveyjp

It is possible with a combi, but you need an excellent flow of cold water and a boiler sized for the flow.  Some also store hot water.

https://www.vaillant.co.uk/homeowners/products/ecotec-plus-combination-store-1152.html#specification

ComicGeek

The only way to guarantee it is to have a cold water tank and pump set to ensure high mains water supply rate, and an unvented hot water cylinder.   

Doesn't matter what the hot water supply system is without the guaranteed cold water flow rate, as it still won't work.

grumbler

daveyjp said:

 Some also store hot water.

https://www.vaillant.co.uk/homeowners/products/ecotec-plus-combination-store-1152.html#specification

And how much water do they store? Obviously not much. We are talking about a bath here.

Rosa_Damascena

grumbler said:

daveyjp said:

 Some also store hot water.

https://www.vaillant.co.uk/homeowners/products/ecotec-plus-combination-store-1152.html#specification

And how much water do they store? Obviously not much. We are talking about a bath here.

I think that needs to stop, its far too wasteful of water.

A standard boiler with hot and cold water storage tanks plus pumps wiill do the job. Am guessing with a combi the tank and option of immersion heater has gone?

Spank

Can't somebody have a bath in the previous evening?

scottishblondie

I would agree with "bloke".  Combi boilers aren't up to the task for scenarios like that.  If we run hot water in the kitchen sink the flow to the bath drops right down.  If I had the choice I'd have an unvented/pressurised heating and hot water system - a system boiler and a huge water tank, which we had at our old house.  2 showers at the same time no bother, and we never ran out of water cos the tank was huge.  Of course all that is rather expensive, and your current pipework might now be up to the task.  So the simplest solution here is probably an electric shower.

Soot2006

We have an electric shower for the very rare situation when two showers are needed at the same time. I say "rare", as the advantage of the combi is that the hot water never runs out, so with a bit of bathroom organisation everyone gets their turn and equally hot water.  Ship showers, my dad used to call them. Water on, drench, water off, lather/shampoo, water on, rinse, water off, done.

Jeepers_Creepers

Hi Brian. To sum up pretty much what's been said above...

1) There are some combis powerful enough to supply two hot outlets at the same time, and they would typically need to be 38kW or over, to supply DHW at 16 litre per minute or more. That will provide for two showers, but bear in mind that showers don't just work off hot water, but blend with cold to provide a stabilised temp. What this means in effect is, your incoming mains water flow rate would really need to be very decent, around 20 lpm or more. And also at a reliable pressure - at least 2 bar, ideally 3+.

2) If you really want to go 'combi' and your incoming mains ain't that brilliant, you can install a mains water booster tank which stores the incoming cold water and then delivers it at the required flow and pressure to your house. These work a treat, but it's another 'box' to find room for, tho' they can go in the garage for example. And this booster will add around £2k to your costs. 

3) The most usual approach would be to store your hot water (so no 'combi') so it can be pre-heated and delivered as needed. Two basic ways of doing this - one is 'vented' and uses the cold water storage tank mounted above it to provide the flow; the higher this is placed the better. If you don't have enough 'head', then you can use pumps to each shower/bath. Personally I hate pumps as they can be noisy and gushy... The alternative way of delivering a good hot flow to two outlets is to use an unvented hot cylinder. This type is sealed and pressurised by the incoming mains, so delivers its hot at that rate (so it needs a decent incoming too). 

4) Folk have suggested instant electric showers in one shower to be run alongside a different shower supplied by a combi. Yes, this will work, but there will be a mad rush for the 'combi' shower because electric ones are pants, especially in winter when it'll struggle to heat a satisfying flow from chilly water. The best instant showers are around 10.8kW (I think that's the max) but that still pales against a 30+kW combi... There are some clever technologies such as air induction (or something like that) used by Mira and others and they claim it gives a better shower, but I have no idea how well these work.

Soooo, if you want to keep your existing combi, then fit an electric shower in the cubicle, and leave the combi for the bath. (I'm guessing you have one bath and one shower?)  If you love combis and want one to supply two outlets simultaneously, then fit a biggie if your incoming mains is great. If it isn't, get ready to fit a mains booster tank.

Alternatively, forget combis and go 'stored'.

Get hold of at least two recommended local plumbers to come out and look at your stats and provide suggestions. (Report back please - it'll be interesting :-)  )