Combi boilers - why the haters?
Discussion
I've just moved into a new place (4 bed detached, 1 bath 2 showers) and am looking at replacing the 20 year old boiler (it runs off 4x47kg propane tanks). The last place we lived in had a combi which was pretty impressive.
Reading some previous posts, it seems like there is a consensus that combis are not really suitable for larger houses with high hot water requirements because of the rate of hot water flow. In the previous place we certainly experienced this e.g. not hot water to bath if someone opens a tap downstairs.
But don't combis have the huge advtange of hot water on demand? No need to heat up a hot water tank in advance and therefore more efficient i.e. only heat the water you use? In the current setup hot water often runs out in the middle of a shower or when filling the bath.
Reading some previous posts, it seems like there is a consensus that combis are not really suitable for larger houses with high hot water requirements because of the rate of hot water flow. In the previous place we certainly experienced this e.g. not hot water to bath if someone opens a tap downstairs.
But don't combis have the huge advtange of hot water on demand? No need to heat up a hot water tank in advance and therefore more efficient i.e. only heat the water you use? In the current setup hot water often runs out in the middle of a shower or when filling the bath.
To answer the question in your title....
Because they don't work anything like as well as a proper hot-water system in 90% of applications.
They are continually specified by people who don't know what they are talking about, because they require less skill to design a system for.
Furthermore a HUGE number of people, including one on here the other day, acknowledge that they don't actually serve their needs, but put up with it.
Because they don't work anything like as well as a proper hot-water system in 90% of applications.
They are continually specified by people who don't know what they are talking about, because they require less skill to design a system for.
Furthermore a HUGE number of people, including one on here the other day, acknowledge that they don't actually serve their needs, but put up with it.
Ferg said:
To answer the question in your title....
Because they don't work anything like as well as a proper hot-water system in 90% of applications.
They are continually specified by people who don't know what they are talking about, because they require less skill to design a system for.
Furthermore a HUGE number of people, including one on here the other day, acknowledge that they don't actually serve their needs, but put up with it.
What Ferg is saying is they are Crap in anything but a 1 bed flat (What they were designed for) Because they don't work anything like as well as a proper hot-water system in 90% of applications.
They are continually specified by people who don't know what they are talking about, because they require less skill to design a system for.
Furthermore a HUGE number of people, including one on here the other day, acknowledge that they don't actually serve their needs, but put up with it.
Fit a bigger h/w cylinder? Do you have a pump on the shower? common a$$hole mistake that, fit mega-turbo-16v-booster shower pump and leave the diddly little cylinder in place.
aside from the above if the hot waters on and the boilers appropriately sized it shouldn't "run out", may drop slightly in temp. If you've got a 3 port valve this will divert the boilers entire output to h/w recovery, if you've got 2x 2 port it won't, but the wiring can be altered to do so, the average plumber won't be capable of this though.
aside from the above if the hot waters on and the boilers appropriately sized it shouldn't "run out", may drop slightly in temp. If you've got a 3 port valve this will divert the boilers entire output to h/w recovery, if you've got 2x 2 port it won't, but the wiring can be altered to do so, the average plumber won't be capable of this though.
hairyben said:
If you've got a 3 port valve this will divert the boilers entire output to h/w recovery, if you've got 2x 2 port it won't, but the wiring can be altered to do so, the average plumber won't be capable of this though.
Most cylinders are incapable of transferring heat at the rate that a boiler can output it, so even an extraordinary plumber would be wasting his time.On the efficiency thing, I'd have thought a properly designed hot tank installation should be capable of holding its heat for days. Should certainly be easy to lag one to the nth degree. It would be interesting to know how much heat is lost through conduction down the pipes that are attached to the tank. Suppose you could really lag those too.
Amateurish said:
I've just moved into a new place (4 bed detached, 1 bath 2 showers) and am looking at replacing the 20 year old boiler (it runs off 4x47kg propane tanks). The last place we lived in had a combi which was pretty impressive.
Reading some previous posts, it seems like there is a consensus that combis are not really suitable for larger houses with high hot water requirements because of the rate of hot water flow. In the previous place we certainly experienced this e.g. not hot water to bath if someone opens a tap downstairs.
But don't combis have the huge advtange of hot water on demand? No need to heat up a hot water tank in advance and therefore more efficient i.e. only heat the water you use? In the current setup hot water often runs out in the middle of a shower or when filling the bath.
1 bath, 2 showers, you'll find out why combi is crap the moment 2 people want hot water, particularly in winter.Reading some previous posts, it seems like there is a consensus that combis are not really suitable for larger houses with high hot water requirements because of the rate of hot water flow. In the previous place we certainly experienced this e.g. not hot water to bath if someone opens a tap downstairs.
But don't combis have the huge advtange of hot water on demand? No need to heat up a hot water tank in advance and therefore more efficient i.e. only heat the water you use? In the current setup hot water often runs out in the middle of a shower or when filling the bath.
hairyben said:
If you've got a 3 port valve this will divert the boilers entire output to h/w recovery, if you've got 2x 2 port it won't, but the wiring can be altered to do so, the average plumber won't be capable of this though.
This is madness.Most 3-ports are mid-pos now, very few diverters so they are never going to put the WHOLE of the output to the cylinder coil if the heating is calling. As Dirk says any common calorifier isn't going to transfer heat at that sort of rate anyway!! Same with an 'S' plan. Why WOULD you wire it to give priority when the boiler is going to be shutting down on it's stat?? While the rooms get cold....
Can't understand this AT ALL. I'm just too average, I reckon.
You do get high flow Combi's
Such as
http://www.worcester-bosch.co.uk/homeowner/product...
http://www.vaillant.co.uk/homeowners/heating-solut...
Pretty big though so you need space (depth)
Such as
http://www.worcester-bosch.co.uk/homeowner/product...
http://www.vaillant.co.uk/homeowners/heating-solut...
Pretty big though so you need space (depth)
ive got the 42cdi bosch in my large 3 bed semi, and i can honestly say, it has been brilliant, it does have a high flow rate, but i believe its quite abit more expensive then the 32kw models ect ect, ive never experienced the water going cold in my home in the time its was fitted 2 years ago to replace my old economy 7 system.
simpo jesus your right, i purchased this old house to do up and the eco 7 was horrific, the combi has been perfectm very high flow rate, but its a big bugger, fills the bath in next to no time scorching hot on its eco settings, it runs my shower with absolutly no deviation is temps, its brilliant. but again it cost a small fortune to buy, and if i could go back id probably go with a conventional system with the solar panels.
Ferg said:
As Dirk says any common calorifier isn't going to transfer heat at that sort of rate anyway!! .
My bad, wasn't aware this required a special cylinder! Can be easily done though, the place had 3x bathrooms all in use at about the same time, for some reason a huge cylinder wasn't practical. Are these cylinders expensive? As for loss of heating, a house with half decent insulation can sustain loss of heat for a while while the water recovers- doesn't a combi do this anyway, ie when you demand H/W for a 20 min shower the boiler diverts all it's power to H/W?
hairyben said:
Ferg said:
As Dirk says any common calorifier isn't going to transfer heat at that sort of rate anyway!! .
My bad, wasn't aware this required a special cylinder! Can be easily done though, the place had 3x bathrooms all in use at about the same time, for some reason a huge cylinder wasn't practical. Are these cylinders expensive? As for loss of heating, a house with half decent insulation can sustain loss of heat for a while while the water recovers- doesn't a combi do this anyway, ie when you demand H/W for a 20 min shower the boiler diverts all it's power to H/W?
Back in the day (young man..
)we used to fit the old V4044 diverter valve, This DID cut the heating out when the cylinder called for heat. It was such a pain that Honeywell developed the mid-position valve to get over this.I have a worcester bosch 35CDi in a three bedroom flat and it works fine. However, it can only supply the bath or the shower at the same time - trying both kills the pressure. Although, both are in the same bathroom, so its not that big an issue. For a flat it is a reasonable price to pay, since space is limited and having a tank would remove a lot of cupboard space.
However, the place we are about to move into we are fitting a megaflow system, because it will have 2 showers. Personally this is the transition point - any more than 1 bathroom and a combi is never going to be up to the job.
However, the place we are about to move into we are fitting a megaflow system, because it will have 2 showers. Personally this is the transition point - any more than 1 bathroom and a combi is never going to be up to the job.
I have a combi in my house, which was specified by an idiot! The incoming flow rate on the cold main is crap, thus the hot water rate is worse. Can't have a shower if the washing machine is on!
I'd much rather in my house have a conventional boiler with a nice big storage cistern high up in the loft feeding a nice big cylinder. With a nice simple 3 port valve set-up, instead of a combi boiler fully of niggly valves, sensors etc.. all of which, when they go wrong ussually leave you without heating and hot water. At least when a conventional boiler breaks down, you can switch the immersion heater on and have hot water!
I wouldn't fit a combi in anything bigger than a 3 bed house with more than one bathroom.
My house doesn't get warm properly in the morning if me and my missus have a shower as its constantly heating the water!
I'd agree with Ferg, most plumbers fit them because there is less to think about and they don't need an electrician to wire them.
I'd much rather in my house have a conventional boiler with a nice big storage cistern high up in the loft feeding a nice big cylinder. With a nice simple 3 port valve set-up, instead of a combi boiler fully of niggly valves, sensors etc.. all of which, when they go wrong ussually leave you without heating and hot water. At least when a conventional boiler breaks down, you can switch the immersion heater on and have hot water!
I wouldn't fit a combi in anything bigger than a 3 bed house with more than one bathroom.
My house doesn't get warm properly in the morning if me and my missus have a shower as its constantly heating the water!
I'd agree with Ferg, most plumbers fit them because there is less to think about and they don't need an electrician to wire them.
Because they are crap and the alledged savings don't exist!
The combi in our house was replaced last year at the ripe old age of 8. Well to be precise the case was 8, everything else in it had been replaced at least once.
With a combi you have no cold water tank, and no hot water tank hence no airing cupboard. Yes you might not be storing hot water in a tank but with a combi everytime you turn on a hot tap the boiler fires up, even if the tap isn't on long enough for the hot water to get down the pipe to the tap. It can't be good for a boiler to be heating up and cooling down as often as a combi does.
Give me a traditional boiler every time.
The combi in our house was replaced last year at the ripe old age of 8. Well to be precise the case was 8, everything else in it had been replaced at least once.
With a combi you have no cold water tank, and no hot water tank hence no airing cupboard. Yes you might not be storing hot water in a tank but with a combi everytime you turn on a hot tap the boiler fires up, even if the tap isn't on long enough for the hot water to get down the pipe to the tap. It can't be good for a boiler to be heating up and cooling down as often as a combi does.
Give me a traditional boiler every time.
The other thing that'd put me off installing a combi is the talk of reducing water pressure to reduce leakage on the distribution system. I dunno if this has been confirmed yet but given it's an "environmentally friendly initiative" that just happens to mean the water boards can keep making large profits for the shareholders with their exorbitant charges instead of investing to maintain & overhaul the system, it's probably inevitable.
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