Are combi boilers rubbish for showers?

[lolawoo]

We currently have a vaillant system boiler, but want to fit an en suite where the hot water cylinder is and don't really have anywhere else to move the cylinder to. Currently we have one (fab) power shower over the bath - will a combi be able to match the pressure of the power shower (assuming no other water outlets being used at the same time)? I know we will need to replace the power shower. It's a 1980s house if that helps.

As long as you have high mains pressure a combi will give one pretty good shower (prob not quite up to power shower standard but still very satisfactory)

Only one at a time though. That is an issue with combis - need to alert the rest of the house not to flush loo/run tap while shower’s in use (With a proper thermostatic shower the temp stays the same, you don’t freeze or boil, but the flow reduces).

I love having a combi. Never run out of hot

Sorry to the above poster but water pressure, more specifically flow rate, has nothing to do with the strength of your shower when it's fed from a combi boiler.

The rate at which your water will flow is entirely dependant upon your wattage, ie how much water your combi can heat at any given time. The higher the wattage of boiler, the more flow rate you have, the more hot water comes out of the shower.

This is assuming you have decent water pressure/flow rate from the mains to begin with.

The higher the boiler wattage, the more powerful your shower.

www.boilerguide.co.uk/articles/what-size-boiler-needed

I'd go for a higher wattage than you think you'll need, but there is of course a cost implication.

Higher wattage, higher price.

what colour is your cylinder?

This is assuming you have decent water pressure/flow rate from the mains to begin with

Yes

Having had poor pressure previously I know the difference!

"As long as you have high mains pressure a combi will give one pretty good shower"

The point is that these two things have nothing to do with each other. The only time a high wattage combi will deliver a poor flow rate is if the mains flow is LOW to begin with, I agree, but as far as I can tell that's not what you were saying. A high (or even average) mains flow rate will not guarantee "one good shower" via a combi unless the wattage is high enough to heat the volume of water needed.

The vast majority of homes have adequate water pressure/flow rate from the mains. Where people get confused is the neccesity for adequate wattage of boilers.

This is why most properties with combos have a lower flow rate from the hot tap than the cold, because the combi is restricting the volume of flow.

Anyway, take it or leave it. :)

Well I suppose I was assuming OP wouldn’t install a boiler without adequate heating power...

people often install combis without having grasped the importance of an ample water flow into the house.

My experience is the opposite, most people I speak to don't realise the importance of wattage of combi affecting the flow from showers etc, but this is all subjective. Both factors should be taken into account.

In answer to the OP, yes, combis can be good for showers but as I've said, (given you have decent water pressure from the mains) the next thing is to ensure you don't get a combi with too low a wattage or no, they're bad for showers.

Most new builds have piss poor showers because the developers have skimped on the combi boiler wattage. Any time I replace a combi, I always go for the next level up in terms of wattage than is generally accepted as standard. This gives a much better (or more powerful) shower, which I like.

Just my 2p. :)

If your have a garage you could fit an unvented hot water cylinder there ( and probably keep you system boiler). Should give you main pressure hot water independent of other taps or heating demand.

@PigletJohn it's yellow, presumably the original one (at least we haven't changed it in the 18 years we've been here). Gives us about 15 mins of hot shower time with the power shower, we would like more really.

@LondonMischief no garage sadly, we converted to a playroom a while back.

So check water pressure from the mains by filling a bucket (what is classed as good pressure)? And buy a decent wattage combi if we do get one (again, what is decent)?

Thanks everyone, it's all just musing at the moment, it might be the cost and hassle outweighs gaining a second bathroom.

The bucket test measures flow, not pressure.

If you can get 20litres per minute from the cold water off the main, that's adequate for a combi or an unvented cylinder (which is likely to be better, depending on how many bathrooms, showers and people are in your house).

Old houses often have poor flow. This can usually be rectified by running a new, larger, plastic water pipe out to the main under the pavement. Digging a trench is not hard, unless there is a lot of concrete in the way.

p.s.

please measure the flow from your shower as well, to give us an idea of what you're used to. A yellow cylinder is often around 100 litres capacity, depending on size. If you got a new unvented one, I'd suggest bigger.

I had a vailliant 937 went for a bigger capacity as had a large shower head and it worked fab. Really powerful and always hoy

until I lived in a house with good water pressure (80 year old house too!) I had no idea what decent water pressure was!

In fact, despite having a well-specced boiler (which fills the bath quickly/gives us a good shower, and we can run the tap too!), we've actually had to have something fitted to reduce the pressure coming into the house, as the boiler couldn't cope with it.

we've actually had to have something fitted to reduce the pressure coming into the house, as the boiler couldn't cope with it

We’re in that position too, Micke - although we haven’t actually done it yet - our boiler’s had a leak every year, & this year for the first time the BG engineer said it was due to plastic parts & high water pressure so we need to fit a governor (or whatever they’re called)

Trouble with our set-up is that there’s no space to fit one anywhere near where the water comes into the house at the front, it’ll have to be in the boiler cupboard upstairs at the back

Before we had our new boiler, I did do the bucket test as outlined above.

We have a Worcester Bosch Greenstar 42cdi classic combi and it gives us a great shower. We have a thermostatic shower. If someone does turn a tap on or flush a loo the flow from the shower reduces but the temperature is maintained. But the flow recovers really quickly.

Something else to consider is that many showers are now fitted with flow limiters. So it might be worth checking out the flow rate of the proposed shower you’re planning to buy. Big shower heads or with more nozzles will affect your flow too.

Eg our shower does 15l/minute and the boiler can heat 17l/minute.

Well, that’s the process I went through.

One more thought. If you’re changing your cisterns, get a fast fill ones.