New boiler advice - to go combi or not?

[ShhTryingToSleep]

Currently got a 20 year old Ideal Standard Classic boiler with Megaflo hot water cylinder in the airing cupboard. Both are starting to give us problems - various leaks in the airing cupboard, a few repairs on the boiler over the last couple of years. I really want to switch to a combi boiler but everyone keeps trying to talk me out of it. The way I see it is, we currently have TWO troublesome appliances - why not switch to one (that will be under guarantee until we probably sell the house in 5 years!)? Otherwise, if we have a nice shiny new boiler then we still have to deal with the crummy old leaky water tank. And I'd imagine it would cost a lot extra to replace the water tank as well. Plus we'd gain a nice big cupboard for other stuff (water tank is huge).

We live in a medium sized 3 bedroom house with 2 bathrooms. 2 adults and 2 kids. Am I really being so unreasonable to want the combi, and am I right in thinking it would be cheaper to do that?

We went to a combi about 3 years ago, and we use around 1/2 of the gas that we used to with the previous 20 year old boiler (4 adults in house). It's made a huge difference - we had to keep replacing the water cylinder due to the hard water and each time resulted in a leak of some kind. This way, I've got an airing cupboard; there is no noisy central heating pump in there and the whole system is so much quieter; and we've always got water on demand. It was a no brainer for us.

Thanks @ConnieCaterpillar70 that's really good to know. Do you have/use a bath? I've heard that baths take so long to fill that you can't ever get them warm enough, that's the only thing that puts me off. But I'm wondering if that just applies to the earlier combis?

How many bathrooms do you have? We used to have a Combi and loved it but could never run two showers at once. Now moved to a house wiry three bathrooms so sticking with water tank (although need to get our system checked as still can’t run two showers at once which we need due to having three daughters!)

Having always had a combi and recently moved to a house with a v old boiler and water tank in the loft, we are counting down the days until we start renovations and can change to a combi again. Hot water when we need it, in the quantities we need it, without the extortionate energy bills. Yes, please! (Granted our system is old which accounts for some of the increased bill costs, but certainly not all)

We have a combi, in a 4 bed, 2 bathroom house and have no issues. We changed from a traditional boiler about 5 years ago when we moved in. We can use both showers at the same time but one is electric. At the time we were also going to replace the bathroom and weren't sure if we'd be putting in an electric shower so got a boiler that would have been able to cope with using two showers at the same time. Obviously never tested that theory though.

We have a huge bath and DH regularly has very full baths and again no issues.

My only complaint is that the hot water can take a while to come through in our ensuite - I'm guessing it's at the end of the line, whereas in the kitchen it's instant (the start of the line)

There are advantages & compromises with both. Personally I prefer the cheapness/flexibility of a standard system boiler/hot water tank.

Worth mentioning that energy use between both types should be broadly the same - big differences will be due to newer boilers being more efficient.
One heats on demand, one heats then stores. Modern hot water cylinders are very well insulated, & any heat that does 'escape' from the cylinder/pipes just goes towards heating your house anyway so in theory reduces the demand on the central heating system by a similar amount.

Also don't forget that with a combi, if/when it fails, that's it - no heating or hot water until fixed.
With a system boiler, you can just flick on the electric immersion on the tank & get hot water. Get a couple of £20 electric fan heaters from Argos & life then goes on pretty much uninterrupted.

It turns an Emergency into an Inconvenience.

First thing we did in our house was replace the old boiler and tank with a new combi boiler. I couldn't figure out how the whole tank thing worked anyway and we now have a lovely huge walk-in shower where the tank was. No problem with baths either.

You say you have two bathrooms and four occupants. A combi will not be ideal.

If your old boiler is old, then you can expect an improvement in economy and efficiency by buying a modern condensor boiler. A common mistake is to think that the new boiler is more economical because it is a combi. This is not the reason. A new boiler is more economical than an old one because it is more efficient. Also, it is usual to update the thermostats, timer/programmer and desludge the radiators during a modernisation, which will also help. Again, nothing dependent on having a combi.

A regular boiler is a bit more economical than a combi for hot water, especially in summer, because you do not have to warm up the boiler and heat exchanger every time you turn a tap on, then let it cool down again after. Modern cylinders are very well insulated and heat losses are minimal.

it is also true that a boiler fault on a conventional or system boiler is a trifling irritation, especially in summer, because you can continue to heat the cylinder with its immersion heater until the boiler is mended.

Combis have more in them to go wrong. I doubt a combi will still be working in 20 years.

Thanks so much for the advice, this has been really useful. Unfortunately our system doesn't have an immersion heater (even got a plumber to check)! Does anyone know how long the hot water cylinders are supposed to last, and if they cost a fortune to replace (ie as much as the boiler itself)? I just feel that it will cost more to replace both things than to just have the combi. Our cylinder has definitely seen better days and like I say causes problems with leaking every now and then, and we'd still be left with that problem even with a new boiler unless we went for a combi.

Modern unvented cylinders are made of stainless steel, with a separate shell over the insulation, so should last a very long time.

The old copper ones usually failed at a connection, sometimes it can be unscrewed and re-made to cure a leak. I've known them 50 years old or leak at 20.

P.s.

Unless your actual cylinder is perforated, I would have thought the leaks more likely to be at pipework connections. So the cylinder may not be to blame.

A new cylinder might cost between £500 and £1,000 to buy plus fitting. I've heard that an external expansion tank is less trouble than the bubble in the older Megaflow, but I don't know about that.

I see 30-year guarantees are available, "subject to conditions"

Looks like prices are higher than I suggested earlier.

Do you have/use a bath? I've heard that baths take so long to fill that you can't ever get them warm enough

I had the water flow turned down so it is really, really hot, but the bloody bath takes 15 minutes to fill - and this is a newish and expensive combi boiler, too. I go away and wait for it to do its thing - very tedious. My father had an older, cheaper combi that was total rubbish. The bath water was never hot enough. Personally, after these experiences, I'm not a fan of combi boilers.

2 adults and 2 kids I wouldn't. I just changed our boiler and kept the hot water cylinder and it is great. We have baths and also a power shower which you can't have though with a Megaflow (in theory shouldn't need).

Our bills have dropped substantially with the new boiler as well despite a cold snap. I wouldn't bother with combi unless you need the space.

What I have noticed with our new Vaillant is how unbelievably quiet it is

Yes, my Viessmann is also very quiet.

Combis tend to be noisier because they fire up at full power every time someone turns on a hot tap.

Mine is a conventional boiler and almost never needs to run at full power.

@ShhTryingToSleep

As for cost here is the cylinder we installed a few years back - an absolute bargain as £684. Includes most pipework and fitting you need so the plumber only needs to plumb in the connections.

www.mrcentralheating.co.uk/water-storage/unvented-cylinders?cylinder_model=32833

I’ve had one for 9 years. In comparison to an immersion heater it’s a no brainier. So much more convenient.

the immersion is only a backup to provide hot water in case of boiler failure. With electricity prices high and rocketing, no-one with an alternative source of fuel would use the immersion.

As long as you get a combi boiler with a good enough flow rate then you can quickly fill a bath with water that's far too hot to actually sit in. The boiler in our last place was only capable of tepid baths but that's what happens when you choose the cheapest option (rented). Our current boiler is a Valiant ecoTEC plus 835 - I have to add a significant amount of cold water to a bath to not scald myself.

We fitted a Vaillant Combi eco tech boiler in Jan 2020 removing 18 year old Ideal boiler, hot / cold water and header tanks.
Being unimpressed at potential losing the airing cupboard we had a small radiator plumbed into the heating in there which is really great in the winter and have no regrets other than the cost of installing with British Gas. We took the view that as we use BG Home-care to maintain the system it was better to pick a system they fitted & supported.

So far we have generally been very happy with our choice never having used a combi before, however we have noticed a drop in hot water pressure if 2 taps / showers are run simultaneously.

The only issue that matters to us is that there is no longer a cold water tank in the loft. Therefore when there is a water supply problem, and we are having lots of water mains repair work in area, the thunder box will not flush and we have no water supplied through taps to drink.
We have addressed these issues by keeping a few litres of bottled water laid away to drink and I have installed a 200 litre water butt in the garden on a down pipe for chucking down the toilet.

Good luck with your choice.

I have a new conventional boiler with a high pressure system - Worcester Bosch. The cold water tank in the loft has gone. I had a combi boiler in a previous house - never again. If you have a large cylinder fitted you can run a bath and a shower at the same time.
Also don’t use British Gas for installation; cheaper to get a loan elsewhere. As for home care; if you buy a boiler with a 10 year guarantee it’s cheaper to save the money you would have paid for cover in case you need it. £160 per year with £60 excess or £230 with £0! That includes a service but I wouldn’t expect a new boiler to break down.

We've had combi in two houses and generally been happy with the set up. The pervious place was a small cottage, so space was at premium and combi was a no brainer. As PPs said, with combi you will notice drop in pressure if two taps are run at the same time. If you opt for a combi, make sure to fit thermostatic shower taps, so that if someone runs a kitchen tap while another person is showering, the water temperature in the shower remains the same.

Combis can usually heat around 12 litres of hot tapwater per minute.

The 35kW Vaillant is a little higher at 14.3 ltrs / min

This is at a Rate at 35 Degree Rise, so the water will be hotter in summer than in winter when the supply from the main may be very cold.

An unvented cylinder can gush it out as fast as your water main supplies it, and the temperature can be just as hot summer and winter.

A bath usually holds around 100 litres of water, depending on how portly Mr. Archimedes may be.

We had a megaflo type pressurised tank fitted at our old house and plan to do so again when we get this house renovated. I loved showers with good pressure and no noisy electric shower pump.