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Combi vs conventional boilers.

(26 Posts)
LovingLola Tue 24-Apr-18 19:03:52

Doing a house renovation and will switch boilers. We currently have a conventional oil fired boiler and are switching to gas.
We have been thinking of a combi boiler with a pressurised pump. Does anyone have one and is the pump going to be noisy? I am afraid that every time a tap is turned on or a toilet flushed that the pump will kick in. Both boiler and pump will be housed in the kitchen....
The alternative is to retain our water tank in the attic and the hot press and just change the boiler itself.

villageshop Tue 24-Apr-18 20:55:25

A combi boiler is a great option if you are short of space but if space isn't an issue then I would always favour the hot and cold tank system.

If you do go for a combi I'm pretty sure the boiler pump won't kick in unless the heating switches on or a hot tap is being used, meaning toilet flushing and cold taps won't set it off.

Waspsarewankers Wed 25-Apr-18 22:16:57

Everyone told us that a combi boiler would be marvellous after years of living in army housing with hot water tank systems.

I absolutely hate our combi. I have had a few plumbers/gas safe engineers out yo check it's ok and adequate for our size home eye. I am told it's more than adequate - if it needed replacing I could drop down a model and that it's in too too condition working absolutely as it should.

I'm pissed off because I run and run and run taps for ages before any hot comes through. Having a water meter with a combi would be a mad idea.

Every time I wash my hands after a toilet visit, out of habit I turn on the hot tsp. The boiler fires up and I eadh my hands in cold water whilst paying for the hot water my boiler eventually heats just sits in the pipes going cold!
Yes you do hear the boiler fire up if in the same room or close by anytime anyone on the house turns on a hot tap/showers (or the dishwasher with a hw feed goes on) but it's not deafening and you do get used to it.
I notice all the new builds in our area (Redrow, Barratt etc) seem to install hot water tank systems these days. If I was starting over with a new boiler eye. I would never have a combi ever again.

iwasjustakid Wed 25-Apr-18 22:24:42

I had a combi for 4 years. Constant issues. Worst bit was when it was broken you'd lose hot water and heating. Never one or the other. Since being in this army house I'm so grateful for the conventional boiler 😂 combi wasn't loud either.

Talia99 Thu 26-Apr-18 17:44:11

I recently got a combi installed and I love it. No more wasting hot water because the tank has heated at the wrong time. Mine is a Worcester Bosch and it can be put on standby so you get instant hot water. You need to balance the extra gas for that against the extra water for not having it immediately available.

Having said that, if you have a large family (i.e. you are using hot water constantly) or if you want to run more than one hot tap at a time, you might be better off with a tank. I’m in a small flat and I think that makes a difference.

Viviennemary Thu 26-Apr-18 17:49:03

I'm not keen on our combi boiler. Prefer the old system but DH said nobody had anything but combis these days. hmm bath water sometimes runs cold which is a total nuisance.

PigletJohn Thu 26-Apr-18 22:21:01

How many people live in the house and might turn on taps, take showers, flush WCs or run washers at the same time?

If the answer is "1" then a combi will be fine.

I am alarmed that you are thinking of using a pump. Why?

bilbodog Thu 26-Apr-18 22:59:58

We have a worcester bosch combi in a 3 bed house and it works fine. Hot water on tap when ever we need it.

LovingLola Thu 26-Apr-18 23:03:00

I am alarmed that you are thinking of using a pump. Why?

To boost the pressure. Is that an issue?

SugarMiceInTheRain Thu 26-Apr-18 23:03:04

I love our Worcester Bosch combi. No complaints whatsoever and a lot more convenient.

LovingLola Thu 26-Apr-18 23:03:56

Also, we have decided to house both boiler and pump outside so the noise issue in the kitchen will not arise.

MrsFezziwig Thu 26-Apr-18 23:09:57

I have had combi boilers for 28 years. Was I an early adopter?
I’m about to have my central heating replaced and was planning to have the new (combi) boiler in a cupboard in the kitchen for ease of access. Do people who have a similar setup think modern ones are noisy? My previous ones were in the garage and loft, so didn’t experience any noise but neither is feasible for my current situation.
I hadn’t considered a conventional hot water tank - if you use all the hot water in the tank does that not mean you only have cold water until it heats up again?

PigletJohn Thu 26-Apr-18 23:28:28

"To boost the pressure. Is that an issue?"

usually the pressure from the watermain is adequate. What is it in your district?

How many litres per minute (fill a bucket and time it) do you get from your cold water tap? How old is the house?

AFAIK you are not allowed to use a pump to suck more than 12 lpm out of the main. Often you will do better to replace your old pipes with bigger ones (especially if they are lead)

hiddenmnetter Fri 27-Apr-18 07:01:40

Just to second what piglet is saying- you’re better off with a system boiler and an unvented cylinder if your mains flow & pressure are sufficient. My builders changed our supply pipe to 25mm for around £1,000 inc VAT (inc digging up the drive and running the 25mm blue pipe).

We get excellent flow and pressure now and hot water is quick and high pressure all round the house. And we have enough hot water to fill the bath 2-3 times on one cylinder.

Chickencellar Fri 27-Apr-18 08:02:19

How big are vented cylinders for those that have them? We were thinking of replacing the combi like for like this year or maybe next. What's the cost like compared to a combi ?

4yearsnosleep Fri 27-Apr-18 08:28:10

I'm having a similar dilemma. We currently have a traditional system with a hot water tank in the airing cupboard. Would it be a direct swap for the boiler & hot water tank. Anyone know what this might cost?
We have 4 beds, 2 bathrooms and we're getting 25sqm of wet underfloor heating in the extension (I already have the cost for that bit) We have high pressure cold water

One plumber quoted £7775 + VAT for both the boiler and underfloor heating which is a lot more than I expected! I was hoping to get it all in for about £5k (+vat if it applies)

Thank you

PigletJohn Fri 27-Apr-18 08:46:03


you say vented cylinder (which is the traditional type fed from a cold-water tank) but perhaps you mean unvented? (the more modern, high-pressure type fed directly from the watermain?

Bearing in mind that a bath holds around 100 litres, and in winter you may need almost all hot water with very little cold, the minimum usable size for any cylinder is about 125 litres (for example, a very common size in older houses is 900mm high x 450mm diameter), which is nominally 117 litres)

But it is more usual, if you're getting a new, unvented cylinder, to fit larger. Usually between 200 and 300 litres. With the improved flow and pressure (subject to your incoming water supply and the size of your pipes) you can then run two good showers at the same time, or fill a bath quickly, or have taps that don't run hot and cold depending what other people in the house are doing.

The boiler will run more quietly than a combi, because it will rarely, if ever, need to run full blast, and most of the time it will be ticking over at modest speed when needed to maintain your radiators and cylinder at the temperature required. You may have noticed that a combi usually starts at max power every time you turn a hot tap on. The more people in the house, the greater the advantage.

Because the boiler runs less often, it is more economical in use of gas, and you are not frequently heating up the mass of boiler and pipework, then letting it cool down again every time. But the cost of hot water is very low, compared to heating a house in winter.

If your incoming water supply is poor, you can have an accumulator to give a limited amount of high-pressure water, or even an old-style vented cylinder and loft tank. This can fill a bath faster than a combi, but shower pressures will be rather weak unless you have a (somewhat noisy) shower pump.

PigletJohn Fri 27-Apr-18 09:01:12

btw Unvented (high-pressure) cylinders are usually white. I often ask for cylinder colour as it gives clues of age and type.

WalkinglikeaFlamingo Fri 27-Apr-18 10:45:19

Worcester Bosch combi here. Apparently there is nothing wrong with it.
Bought house with it in 2 years sgo. First experience of a combi boiler after always having hot water tank systems.
Not impressed at all. We have been told our boiler is "above spec" for our house/number of bathrooms and working as it should be. However, the instant hot water a combi boiler is supposed to provide takes a very long time to reach the tap. The amount of cold water we let just flow down the sink waiting for the hot to kick in is terrible.
I cannot recall the last time I washed my hands in warm water after going to the toilet. If I had the time and inclination I could stand and wait for several litres of cold water to flow down the plug hole until eventually it warms up but its too wasteful and time consuming. It pains me to think that what I'm paying for is my hot water to lie in the pipe somewhere in the system where it will go cold before ever reaching the tap.
Likewise to run a shower, I switch the shower on then have time to go to the toilet, get fresh towels, open the window, sort laundry onto lights and darks piles before it's hot enough to get in. So wasteful and a reason why we have not gone on a water meter in this house.
No immersion, so of your boiler plays up you have nothing. No hot water as well as no heat with a combi.
I would love a tank system again. Just make sure you get an adequately sized tank for your needs would be my advice if choosing a tank system.

OctoberOctober Fri 27-Apr-18 11:29:25

We have had both systems and on the face of it my pref was for combi. But the points about waiting for 'instant' hot water are true, plus we found the pressure worse when running a bath with a combi.

We have just put in an unvented and find we are only heating the water for 30 mins a day, it keeps hot all day and 250l seems to be enough for us (4 people). On that basis, I'm interested to see how the bills compare but I'm not expecting high cost for water heating.

Toomanycats99 Fri 27-Apr-18 11:36:22

I have a combo. The original one in house was not powerful enough and running baths was a nightmare there was a perfect spot to turn the taps on enough to get hot water without too much flow that came out cold. We now have a new more powerful one. Downstairs bathroom water is fine - comes out hot pretty quick. I do notice a delay with the heat coming up 2 floors.although once it gets there it's fine.

Chickencellar Fri 27-Apr-18 12:11:43

piglet John
Yes that's correct , thank you for your advice and thoughts. Space is lacking in our house to put a cylinder in. Something to think about. Might post a thread when we get round to quotes .

Chickencellar Fri 27-Apr-18 12:13:20

Separately I do wonder how for 20 years or so combi s have been the way to go for a majority of houses. Most people I know have these installed.

vickibee Fri 27-Apr-18 12:16:21

Vaillliant conventional boiler here, it is great but we were advised this was the best option for a larger property with two bathrooms.

PigletJohn Fri 27-Apr-18 13:08:40


Might be the fact that they're relatively quick and easy for installers to put in, plus they can take away your old copper cylinder and some pipes to sell for scrap.

The short life of combis ensures plenty of repeat business

When they fail, customers have no heat and no hot water, so even in summer they are desperate.

Opinions vary, of course.

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