Advice on combi boilers

wendyb_4 · 7 August 2006 at 6:08PM

Hi,
My partner & I are buying a 1930's semi - which has an oldish gas boiler. Is it worth fitting a combi boiler? Are they as efficient & do you get as much hot water? I've read somewhere that in a house with more than 2 bedrooms they are less efficient than a standard boiler with a tank. Any advice would be very much appreciated.
Thanks .
Wendy

Dandirt · 10 August 2006 at 11:55PM

If your existing boiler is oldish then any new combi or standard boiler is going to be more efficient - mainly because it is going to have to be a condensing boiler, which is specifically designed to be very efficient to meet stringent new regulations.

As a Corgi registered heating engineer I install about two boilers a week and 99.9% of them are combis. I have a big-ish house myself (4 bed, 17 radiators) and I have a Baxi 105HE condensing combi fitted which works just fine.

For me, the advantages of a combi are - simple system, no stored water in the loft, mains pressure hot water, clean hot water (not stored in tanks), cheap boilers to buy and easy to maintain and repair when something does break.

Not everybody likes combi boilers though and there are many different ways of providing a domestic hot water supply - mains unvented, thermal store, high recovery rate cylinders, etc. etc.

Not quite sure what the number of bedrooms has to do with the efficiency of the boiler but if efficiency is the primary concern then bear in mind the other factors which will affect the gas bills. Things like insulation and proper time and thermostatic control so that the heating is not on when you don't need it and also shop around for your gas supplier - I just switched using info. from this site and saved a whacking 40% over my previous supplier.

Good luck

jennifernil · 22 August 2006 at 6:10PM

I like to have some back-up so would never consider a combi-boiler. If it fails you have no hot water at all.

AceT · 23 August 2006 at 8:49AM

In relation to this, we've recently had a combi condensing Worcester Bosch fitted and since then have lost pressure from the taps when more than 1 water source is used. The hot water cylinder has been removed so everything goes through the boiler. The electric shower now fluctuates from hot to cold especially when a tap is opened anywhere in the house and also the bath taps are not as high pressured as before. If I open the hot then open the cold then I lose pressure in the hot thus filling the bath takes a long time. Any advice???

Do we need to stick in the cylinder again to have hot water instantly upstairs?

It also takes a while for the hot water to come out the taps. Is this normal? Can take about 30 secs.

5 bed detached house, about 12 radiators.

bestyman · 23 August 2006 at 9:12AM

I agree with Dandirt about combis but would add some have a better flow rate than others ( thats the amount of hot water that can flow from taps in litres per minute) .
With a hot water tank you have stored hot water so if 2 taps are turned on at once they both flow well. With a combi there is no stored water as it is heated up as it passes through the combi boiler so tthe flow is only as fast as the boiler can heat it up .
For the above resons a traditional cylinder and tank or other type of hot water system will provide better hot water flow than a combination boiler ( esp. the cheaper ones with lower output) .
As Ace T says there will be a delay for hot water to arrive as the combi only starts heating water AFTER the hot tap is opened .- no solution to this other than have stored hot water.

To complicate matters it is possible to have a combination boiler but still have stored hot water. Its quite unusual unless you have a very large house but IMO is the best way to go if you like loads of hot water and have a few quid to spend.

Bestyman

Slim · 23 August 2006 at 9:20AM

I think that in next months issue of Which there is a feature on combi boilers looking at their efficiency etc.

Cardew · 23 August 2006 at 11:34AM

Combi boilers do have several disadvantages IMO; some of them mentioned above.

I have a combi in an annex and find in winter, when the input water is cold, the water from taps is not very warm unless you turn down the flow a lot. If you look at the specification of some(most?) combis you will find that they raise the input water temperature by 35C at xx ltrs/min.(do not confuse with the CH water temp) Well if your input water is 5c that is only 40C.

Skiduck · 23 August 2006 at 1:53PM

some combination boilers, such as the potterton performa 28i/baxi combi instant 80e and 105e have a pre-heat feature, giving you 65 deg immediately, with the pre-heat feature off, or no preheat feature the instantaneous draw off is at about 35 deg.

msmicawber · 25 August 2006 at 12:29PM

I've lived in houses with a variety of different types of boilers, and one disadvantage that I found with the combi boilers was that you have no clothes airing facility because you don't have a hot water tank. Fine in summer, but a real pain the rest of the time. Do you have the space to have things airing around the house? Will you end up doing what most people I know do, which is then to get a tumble drier and spend more money/waste more energy than is saved by having the combi boiler?

Gorgeous_George · 25 August 2006 at 12:45PM

My experience was that my combi did not provide much hot water. It was always breaking down for minor repairs that proved expensive to fix. I prefer to have a traditional hot water system and my current gas-fired back boiler seems fine (touch wood).

Biggest benefit to me of the combi was always having hot water available, especiially after holidays. No need to set a timer to decide when to have it available. Other advantages included not having a copper cylinder that filled with limescale and needed new immersion elements far too often. Other than the costs of repair, it was more efficient.

Disadvantages included loss of airing cupboard, unreliability, poor hot water pressure. I'm sure they've come a long way since the days of my Chaffateaux Celtic.

If I replace my back boiler, it will be with another back boiler.

GG

Skiduck · 25 August 2006 at 1:07PM

I think the best advice for anyone may be:
If you've had a combi before or have any experience of them and liked it, get another one.

If you haven't and your existing system does you well, don't change - unless you are looking at a sealed system with and unvented cylinder - the best systems on the market IMO.

Advice on combi boilers

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