combi versus conventional boilers

You have probably had this discussion here many times before but is
there a perceived wisdom about which is better?
The subject arises as my grown up daughter has just moved into a house
with a conventional boiler and she was going on about what a nuisance it
was that the house did not have a combi boiler. My initial thoughts
were why complain? - is the combi so good that you'd choose to be with
one instead of conventional boiler?
I have never found it very satisfactory whenever I have come across a
combi boiler but on this occasion kept quiet as I imagined that things
had improved since my last experiences. And anyway who wants a Dad who
is out of touch.
Pro combi boilers:
Less capital expenditure than conventional
No hot water cylinder
Usually controls are within the combi casing including pump which saves
wiring and /or space and helps to keep cost down.
Mains water is used to supply the hot water so that it can be reasonably
powerful once set up.
Saves heating a (perhaps) unwanted cylinder of hot water which may be a
waste of fuel.
Pro conventional boilers
No need for a constructed airing cupboard ( the ones I have come across
have a very small radiator at the bottom) - build one over the
Heating of space at the same time as the heating of water to supply hot
water. (In my case a considerable advantage as it is at night when the
whole family wants a bath or shower in readiness for the next day).
(This allows me to go into a heated room to get dry and dressed which is
a nicety but also allows the bathroom to be prepared for the next person
- also the house does not go a bit colder.)
Filling of a bath from a cylinder can be quicker than a combi can fill
the bath.
Often cited as the solution to a longer boiler life than the combi and
also may be needed for larger houses or condensing boilers.
Allows a cylinder full of water to use if needed when the water supply
becomes very poor. (Boil for drinking or use for flushing). Also
allows for hot water and heating if needed if the mains supply pressure
or flow rate drops e g. in some London flats in summer drought mind you
there are solutions suggested for low flow rate.
I suppose my primary motivation for asking how people regard them is the
fact that we recently rented a house for a month and it had a combi
boiler. No doubt the owner saved quite a bit putting that in. The hot
water in the bathroom was always OK and the house was warm and cosy but
the pipe route and the boiler settings meant that the kitchen was a pain
in the neck for hot water - always needing great care in hot water use
and despite an econo setting had to be run to get hot.
Reply to
Paul Kelly
Some combis can fill 3 baths simultaneously.
Want a combi that is ultra reliable? They have them. Try an Atmos, even with an integral weather compensator. Others, Viessmann, ECO-Hometec, Atag, even Vaillant aren't bad.
Want one that fills a bath as fast as cylinder? Mainly floor mounted: ACV Heatmaster, Gledhill Gulfstream, Viessmann 333, etc. Wall mounted: Alpha cd50, Viallant 937.
Want one that delivers water instantly without the combi lag? Many around with integral small water vessels.
Combis are so go these days that if you have good mains pressure and flow it is difficult to justify other forms of CH and DHW. Just get the right flowrate and a high quality product. Get one that is undersized in flowrate and poor quality and you have problems - same as any other product.
Reply to
Doctor Drivel
I cannot figure why many new (and very small) flats have convetional system. Space is absolutely critical yet they putin this dirty great big cylinder.
Reply to
I suppose a combi is useful if your life is so unpredictable you can't set a timer for the hot water and sometimes need a shower *instantly*.
A stored hot water system is easier to provide a back-up by way of an immersion heater.
A useful possibility is to use a combi boiler to supply a mains pressure shower, but also to have a hot water cylinder branched off the radiator output.
Reply to
In article , writes:
Combis require a good mains pressure and flow rate. That's not available everywhere, and Thames Water have warned they are reducing pressures in some places where it is currently OK. A combi is also one basket for all your eggs, which is not necessarily a brilliant idea if the place is being rented out.
Reply to
Andrew Gabriel
Nope - neither is better - it all depends on what you want, expect, your circumstances and budget. Each have pros and cons.
Depends on the limitations of your conventional system. If the controls are badly implemented, or the cylinder undersized or very slow to recover then a combi may seem preferable. If you want showers in preference to baths the availability of mains pressure hot water may seem attractive without the need for an unvented hot water system or pumps etc.
Some are better than others certainly. The thing that throws many people is that you can't just turn the bath tap full on and get hot water out of it - usually you need to trade off flow rate against temperature.
Probably true, so a favourite with builders.
May be good or bad depending on circs.
A system boiler does this as well - it is like a combi without the instant hot water bit.
Note also there is nothing stopping you using a combi to heat a hot water cylinder just like a "normal" boiler. That can give he best of both worlds - high pressure hot feed to showers, and unrestricted flow high temp water to a bath.
If your cold main is any good...
Lagging fixes that if you are storing.
Could do... although a dehumidifier will make a far more effective drying environment than an airing cupboard.
That depends on how the controls are wired. It is not uncommon to give priority to hot water even on a stored water system.
Typically true unless you go for a semi industrial combi, or are comparing with a poorly implemented storage system.
Well any boiler you fit will need to be condensing these days.
Well long pipe routes can blight any system. The econo setting on the combi probably disabled the facility that some have to keep a small reservoir of water hot for instant delivery.
Reply to
John Rumm
< long post snipped >
I do miss my conventional boiler (Baxi Bermuda gas fire with back boiler) but my Worcester Bosch combi installed 8 months ago is using a lot less gas. The estimates based on my old boiler are way over the top to the extent that I am £20 in credit on my gas bill. I can't say how long it will take to recoup the cost of the combi installation, or whether I will ever recoup the cost, but since the old boiler was an uneconomical repair, and I didn't qualify for a conventional boiler replacement, I had no choice but to have a combi. So, on the basis of cost alone, my experience is that the combi is much cheaper to run.
Reply to
I cannot figure why many new (and very small) flats have convetional system. Space is absolutely critical yet they putin this dirty great big cylinder.
Reply to
Doctor Drivel
More old wives tales. Some combis can fill a bath faster than a gravity cylinder system.
More old wives tales. Some combis can fill a bath faster than a gravity cylinder system with no loss in temperature.
Space saving is always a good thing.
Or just buy a higher flowrate combi if the mains can cope.
"semi industrial combi"? More old wives tales!!
Reply to
Doctor Drivel
It is possible to fit a small 80 litre, pressurised, thermal store in tandem with a combi. This is heated "directly" by the combi using a normal cylinder two valve setup. This improves the flow considerably. The small thermal store cylinder's coil can be before the combi in the DHW line, or after. Best before the combi, inputting hot water into the cold DHW inlet of the combi (see makers whether this is possible, as some are and some not). Then the flow rates are high and you never run out of hot water. When the store is depleted of heat the flow reverts to what the combi alone can supply.
The small cylinder can be fitted above or below a wall mounted combi not taking up the masses of space a vented 140 litre cylinder would take up, which also needs a cold water storage tank. It takes up 550mm in dia and 600mm in height. These are ideal retofits to poor flowrate combis. They also give electric backup to a combi system too.
Look at:
Reply to
Doctor Drivel
In article ,
But that's little to do with it being a combi but replacing a really inefficient non room sealed unit with a condensing one. The gas usage saved by a combi over a storage system is insignificant.
Reply to
Dave Plowman (News)
In article ,
You've been trying to get this point across for several years. Here is one such post you made under one of your many aliases :-
From: Adam Subject: Re: Combi or Conventional boiler? Date: Thu, 03 Feb 2000 12:05 Newsgroups: uk.d-i-y
There are high flow combis. Some meet the 16 litres/min that British Standard lay down for bath taps and fill the bath just as fast as any other system. Combis can give high flow!!!!!! People on here talk as it they can't and never will.
If occasional high repair costs cancel out the cheap running costs so what's the problem? You still have power shower type of showers and lot of valuable space liberated. For every person that has had a troublesome combi there are far more that have had no problems at all year after year.
At least on that one you mention how you've worked it out - a random standard chosen to represent an average flow rate. Which is heavily biased to favour combis. As it would be a very poor storage system indeed that could only manage 16 litres a minute of warm water.
Reply to
Dave Plowman (News)
Assuming that you are not trolling as a festive prank....
There is no "one size fits all" solution to heating and plumbing. The main FAQ and Boiler choice FAQs have some info them. There is are multiple questions to be answered. Very very very roughly as a starting point flat-> combi , house -> non- combi.
End user life-style, budget, previous experience and prejudice are veyr significant factors.
Reply to
Ed Sirett
Well in the new build stuff I see, the cylinder is an unvented unit which offers HW at both mains pressure and usually with a good flow.
Reply to
Ed Sirett
It still takes up valuable space, and is unnecessary in a flat using a high flow combi. Developers are not aware what is on the market, that is why they install inappropriate equipment.
Reply to
Doctor Drivel
That is true. However in the average British house with good mains flow and pressure, a combi model will do what the owner wants and even more. It is knowing what is on the market and what they can deliver. Combis are so comprehensive in the ranges available it is difficult to justify any other type of heating/DHW.
....and 20 years out of date.
Reply to
Doctor Drivel

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