Why doesn't everyone hate combis?

Grenage

Our last house had a combi, and it was fine. Great shower pressure, quick to heat water, no problems.


Current place has 25yr-old conventional boiler. Great power-shower pressure, instant hot water, toasty airing cupboard.


If the boiler exploded I'd have to give some serious consideration to a combi. It would suck to lose the power shower, but that thing is so noisy it would be an issue if the bedroom that that houses it had an occupant. We might also want to extend into the other half of the loft, so the tanks would ideally need to go.

shortcrust

One thing I don’t miss about having a water tank is the sound of it refilling as I settle into a lovely warm bath. In my previous house it made quite a racket for five mins or so. Now with a combi boiler the house is silent as soon as the tap is turned off.

fred246

What you are trying to get with a combi is a constant output hot water temperature regardless of varying flow rates. I think that's very hard to engineer. Given the difficulties in achieving that I'd rather go with a system that will naturally produce a constant hot water temperature once the initial cold has run off.

System

Ganga wrote: »

We also have an airing cupboard,its larger now the big copper tank is out and we have a combi:rotfl:

Ditto! We now have a decent sized cupboard, all shelved out, with a low wattage panel heater on the back wall, plugged into a timer switch.

We also have a combi boiler / central heating system which doesn't have any of the issues mentioned in the OP's post. It's in the garage, so it doesn't even impinge on our living space.

[Deleted User]

•Long delay (typically a minute or so) before hot water comes out of a tap.
When I ordered my combi two years ago I wasn't particularly bothered by the prospect of a delay because I was used to the delay with my multipoint. I was a bit taken aback to find the combi is slower though, as it has two heat exchangers and therefore takes more to warm up. My combi has a keep-warm function though, to provide instant hot water if you want it.

•Flow-dependant temperature, sometimes meaning that for properly hot water, only a slow flow can be used.
This was a problem with my old multipoint, because it had a fixed 22kW burner and no control system. The combi has a 28kW burner with an electronic control system, so it's not a problem.

•Bizarre and infuriating tendency to slow down the hot water flow until eventually it is a trickle, at which point the boiler switches itself off and (having wandered off to do something else) you come back to a cold trickle coming out of the tap!
This is the tap, not the boiler. When a tap is closed, the washer is compressed against the tap seat. When it's turned on, the pressure on the rubber is released, and it slowly expands, reducing the flow in the process. My cold tap does just the same, albeit a bit more slowly.

•Pause the hot flow even for a moment, like if you accidently knock the shower lever, and the damn boiler immediately shuts down. You then have to wait (again) while the water goes alternately hot and cold until the wretched thing has got its life together.
The old multipoint did, but the combi's less of a problem because the additional delay works in your favour, smoothing out the variation.

•And of course during the household's morning ablutions, the boiler can only do one thing at once, so the central heating goes off and the house goes cold...
No it doesn't, the house can't cool down that quickly.

coffeehound

Dan-Dan wrote: »

Absolutley bizarre, you obviously have not met in your life a decent plumber who can help you with the obvious system faults you have been unlucky enough to have 6 or 7 times :think:

That's renting for you!

Grenage wrote: »

If the boiler exploded I'd have to give some serious consideration to a combi. It would suck to lose the power shower, but that thing is so noisy it would be an issue if the bedroom that that houses it had an occupant. We might also want to extend into the other half of the loft, so the tanks would ideally need to go.

shortcrust wrote: »

One thing I don’t miss about having a water tank is the sound of it refilling as I settle into a lovely warm bath. In my previous house it made quite a racket for five mins or so. Now with a combi boiler the house is silent as soon as the tap is turned off.

An unvented hot water cylinder or vented heat-store would give power-shower performance without a whiney pump, and no need for cold feed tank in the loft making noise as it refils :cool:

coffeehound

jack_pott wrote: »

•Bizarre and infuriating tendency to slow down the hot water flow until eventually it is a trickle, at which point the boiler switches itself off and (having wandered off to do something else) you come back to a cold trickle coming out of the tap!
This is the tap, not the boiler. When a tap is closed, the washer is compressed against the tap seat. When it's turned on, the pressure on the rubber is released, and it slowly expands, reducing the flow in the process. My cold tap does just the same, albeit a bit more slowly.

Thanks Jack, you are one day late with that info as mentioned in post on the previous page! There is definitely a strong thermal effect in my experience though; it's not something I've noticed happening with cold taps. Anyway I'm going to change all the tap washers and see if that helps.

jack_pott wrote: »

•And of course during the household's morning ablutions, the boiler can only do one thing at once, so the central heating goes off and the house goes cold...
No it doesn't, the house can't cool down that quickly.

When there are six people needing to take a shower just at the time when you need the heating to warm up the house first thing in the morning, it most definitely is a disadvantage of combis.

Norman_Castle

patman99 wrote: »

I used to work on a new-build estate and every house has a large tank installed as well as a combi boiler.


I spoke to the plumber who told me that the ch feed runs through a coil in the main tank. This heats up the water. This, in turn, acts as a heat reservior pre-heating the ch water before it goes back through the boiler, thus reducing heating costs.

missile wrote: »

Que? That sounds like BS. :rotfl:

It cost what it costs to heat water to whatever temperature. Even a well insulated tank looses heat.

My previous system was as above with a valve similar to a trv for the tank. The water was heated by both the gas heating coil and topped up with electric.

[Deleted User]

coffeehound wrote: »

it's not something I've noticed happening with cold taps.

That's because materials creep less at lower temperatures.

The effect of creep is also less noticeable when the water is on a low pressure tanked system than it is on a high pressure mains supply. This is because for any given flow rate, the tap needs to be opened further at low pressure so the creep on the washer is a smaller proportion of the size of the opening that the water passes through.

Lgas

I completely agree, much prefer a conventional system any day of the week - my OH agrees, and we are both gas engineers.