Combi boiler or boiler and separate water tank

[user1471462428]

Just looked round a house and the estate agent tried to convince me that having a boiler and hot water tank is preferable to having a combi boiler??? Isn’t that rubbish or did he have a point??

Boiler and unvented hw cylinder - good pressure for showers, hot water when needed but no problems when another tap etc turned on in the house plsu no tanks in the loft. I think this is preferable to combi or boiler and loft tanks.

beware of comparing a modern system of type X with a 30-year old system of type Y.

X may be better than Y, not because X is superior in concept, but because it is more modern and powerful.

Modern boilers are often twice the power of old ones, but modulate their power down automatically according to demand.

Heat losses from a modern insulated cylinder are negligible. You actually lose more from a combi because every time you turn a tap on it heats up the boiler, and then all that hot metal cools down again.

This is really interesting I’m glad I asked. Think I may well ask the neighbors whether they have kept the system and have any problems getting parts. My bull shit radar was blinking as he’d contradicted himself several times about how many viewings there has been but he might be right with this.

tank if you have the room. provides backup if bolier goes ( immersion), still have hot water if you get a power cut and had warning ( not unknown here) and hotter water. not hard to set a timer for hot water.

My current boiler is about 17 years old and engineer told me gradually the parts do become harder to replace as they are stopped being manufactured. I’m looking to replace the boiler with a new, more efficient one and a new hot water tank, but we don’t really NEED a new hot water tank, I just want it all done at once.

After having lived in 2 houses with combis & 2 houses with a separate hot water tank I'd always go for that option.
You get a hot airing cupboard, if your boiler fails you can still have hot water if you use the immersion heater. This has happened a couple of times & I have always been so grateful for it

20yr old hot water tank Vs new combi - personally I'd far rather the combi.

I lived in a house with an old water tank - it was a bloody nightmare - couldn't get spare parts and had to do patch up jobs with parts that weren't quite right, the immersion no longer worked and the seperate boiler was temperamental at the best of times. We had no heating and no hot water quite a few times.

An ordinary hot water cylinder has practically no working parts in it, and you can still get parts to fit cylinders 50 years old.

Perhaps you had a special one.

Doesn’t it have the heater inside it though? I thought the newer ones had heaters with much greater surface area to heat it much more quickly? If not, I’ll scrap that idea!

The cylinder (usually) has an electric immersion heater inside it. This screws in. It can be removed and replaced with a new one if it goes wrong. I've seen them still working after 50 years. The thermostat that fits inside it is also replaceable (without needing to drain any water). They last less long.

The cylinder (usually) has a copper tube in it, coiled. The boiler heats the inside of this coil, and the heat passes to the tapwater in the cylinder. The coil (almost) never goes wrong. If it does, you buy a new cylinder.

Modern cylinders come pre-insulated, and have a bigger coil than old ones so they heat up faster (modern boilers are usually much more powerful than 50-year-old ones so can supply more heat). They are sized so that a powerful boiler can notionally take the cylinder from cold to hot in 20 minutes (but in practice they usually take longer).

The modern unvented (high-pressure) cylinder is usually chosen to be larger than the old ones, so it can run at least a bath and a couple of showers, and a day's washing up, without running cold. But as they heat up quickly, by the time you've run your bath, wallowed in it, got out, towelled dry, and brushed your teeth, it will be replenished.

It is a bit more economical on gas to heat it once or twice a day rather than continually, because the boiler runs less often. In winter it doesn't matter, if the boiler is running anyway to do the radiators.

We currently have a boiler with a HW tank. Coincidentally I had BG out today as the heating wasn’t coming in (but we thankfully had HW) and I was chatting with the guy about replacing it and when looking at the flow rates of a Combi, they are far less than what we current have (20litres versus 12/13 litres) so I don’t think we will be swapping any time soon as we have two showers which can operate at the same time currently, which is handy!

I know there are high flow combis available but they are eye watering my expensive in comparison to the standard ones.

We have just moved into a property that needed a new boiler (old owner had jammed the previous one so it worked 🤨) we opted for a tank as the old boiler didn't actually fill the bath and we intend on putting in 2 more ensuites so a standard combi wouldn't have been enough for our needs

We used to have a boiler and a separate hot water tank in the airing cupboard. When we updated the boiler, the plumber persuaded us to have a combi. Bad mistake.

It is bloody awful. Not only do we not have a proper airing cupboard any more, you have to run the hot tap for ages and waste a load of cold water before it runs hot. And our combi is only about 2 feet from the kitchen tap.

Never again - we are thinking of changing back to a traditional set-up.

We have a tank. Dh is a plumber and gas engineer and he says the tank is more preferrable as if the boiler breaks you still can have hot water.

Many parts on boilers are special order only and therefore if your boiler breaks and its a combi that can mean sometimes 10 days with no hot water or heating as its quite often the case that when boilers break it requires a special part then it can be real inconvenience.

If you have a tank then at least you can have a shower whilst you wait for the boiler to be fixed

I used to have a separate water tank and boiler. Now I have a combi. There are pluses and minuses to both. The combi works better and is cheaper to run but makes a bit more noise. Whereas the old boiler and water tank was better because if the boiler stopped working I could still get hot water via an emersion heater, so the boiler breaking during the warmer months wasn't a problem. Both of them made the water hot enough.

How big or small are these tanks ? We have a combi but in the future could move to a tank set up. We don't have much spare space mind.

@NameChanger22

when you say the combi is cheaper to run, are you comparing a modern to an old boiler? Modern boilers are much more efficient, regardless of type.

@NameChanger22

A bath takes about 100 litres of water. If you are a trifle portly, less because you use up more of the space. In summer, particularly, you will add a certain amount of cold. Cylinders don't heat right to the bottom, so I'd say the minimum size is 125 litres. But 250 litres and larger are more usual, especially if you have multiple bathrooms and shower enthusiasts.

There are some examples on here

The white ones are unvented, they have a double case, with insulation between. To get the best out of them, you need very good incoming water flow from the watermain. In an old house this may mean some re-piping. The blue ones are vented and are supplied from a cold water tank, typically in the loft. Although they can deliver water at a high rate (maybe 20 litres per minute depending on your pipes and taps) the pressure will be low leading to weedy showers unless you add a shower pump.
www.screwfix.com/search?search=cylinder#category=cat830950
Height and girth vary to give the different capacities. Horizontal ones are not as good.

when you say the combi is cheaper to run, are you comparing a modern to an old boiler? Modern boilers are much more efficient, regardless of type.

Yes I am. When I got our new combi boiler my gas bill nearly halved. But that was a long time ago and my gas bill has never risen since then. I'm still paying a lot less now than I was 15 years ago, when I had the old boiler.

Our combi might use less gas than the old one, but we waste a hell of a lot of water waiting for the taps to run hot.

Lived in a house once with combi boiler. Hated it. Had to run the tap in the kitchen for ages to get hot water. What a waste of water and time. No airing cupboard.

Had to have new boiler a few years ago. Insisted on one with tank and airing cupboard. Essential in the summer to air off clothes and bedding that have just been ironed since you don’t want them bone dry before ironing and no hot radiators to use as you can in the winter. Washing never smells right if not properly dry and aired.

WE have a Combi, runs a very good shower but we are not shower conessoirs, even if someone turns on a hot tap it doesn't affect it noticeably but i ran separate pipes to each outlet.
We never use the bath so we don't care too much about flow rate, but it does take longer than we'd like to get hot water at the taps in summer. You can set a preheat mode to keep the boiler warm all the time but that wastes more gas then having a hot cylinder.
For those who think an airing cupboard is important, just put a towel rail in a wardrobe and you've got the same thing only with more space.

Combi are really only for ease of installation, when space is thight, if you live alone, have low flow through you mains, or if you have lower expectation on what a good shower is. Also if your boiler fails, your out of hot water and heat.
If you have the space a system boiler and an unvented hot water cylinder will give instant hot and cold water both at mains pressure. And you can have hot water and heating at the same time. A thermostat in the cylinder will ensure hot water is always ready to go. The cylinder does not have to go in the loft, you can have it the garage or anywhere else.

I’d be interested to know what people have paid for system boilers? I’m definitely not replacing mine with a combi but I have been quoted around £2.5k for a Worcester combi to service a 4 bed/2 bathroom house

My plumber told me what to order online and he fitted it. ViessmannVitodens system boiler ( he was Austrian and would only recommend German made boilers) was about £1000 and a 300l unvented cylinder was about £600. Took two of them 2 days to fit and commission for £800. Our boiler is it the garage and water tank in the loft for a short run to the bathrooms in the upper floors ( hot water is as instaneous as you can get). Some extra for copper piping and fittings.

We've been told to go for a megaflo which is apparently a bit of a tank and a combi boiler. Anyone used one? Any good? They seem pricey but we are heating 3 floors of old house plus 3 bathrooms....,