Combi Boiler advice

[tjlglass]

I have a boiler at the mo that was installed in the 1970's and our Gas bills seem exceptionally high. Was thinking of changing to a Combi Boiler and have had a few quotes. The lowest one was 1,600 and the highest just under 2,000. I know absolutely nothing about these type of things and any comments would be welcomed ?

[Idris]

Not really my area of expertise, but what I think is important here is to go for a high-efficiency, condensing boiler. That way you will get the most energy out of every unit of fuel (be it oil or gas) which you buy in. A balanced flue also helps with heat recovery and nudges the overal thermal efficiency up even more.
As to whether a combi unit is a good idea, all I can say is that I've had two of them and never had any problems (except for the three-way valve failing). You need to make sure that hot water has priority over the central heating (unless you like cold showers!) and also ensure that the hot water tank provides a big enough buffer for your requirements. If you don't aleady have a combi system, remember that you will need to factor in the cost of the necessary modifications to your hot water pipework too.

[tjlglass]

Thanks Hugh at the mo we got a tank in the loft and another tank in the airing cupboard and according to the plumber that will all go. He has quoted for a 30kw combi so I think I will go for that. I will have to sell a few toys to get the money together so keep an eye on my eBay site.

[fixer]

Get a big kettle and some hot water bottles

[motorman]

My understanding is that the whole point of a Combi-boiler was to do away with the need for a storage tank. With a combi you only heat water as and when you need it.

[Idris]

My understanding is that the whole point of a Combi-boiler was to do away with the need for a storage tank. With a combi you only heat water as and when you need it.

No. A combi boiler does both the central heating and the hot water, with the hot water from the boiler being diverted into the appropriate loop by a three-way valve. There is still a hot water tank and the contents are heated by the water from the boiler which passes through internal coils (i.e. the hot water from the boiler and the hot water which comes out of the tap are kept separate).

[motorman]

My understanding is that the whole point of a Combi-boiler was to do away with the need for a storage tank. With a combi you only heat water as and when you need it.

No. A combi boiler does both the central heating and the hot water, with the hot water from the boiler being diverted into the appropriate loop by a three-way valve. There is still a hot water tank and the contents are heated by the water from the boiler which passes through internal coils (i.e. the hot water from the boiler and the hot water which comes out of the tap are kept separate).

Not in my house. My hot water tank was ripped out years ago! Hot water is now on tap straight from the combi itself. It only turns on when i turn a tap on. Great idea!! Beats heating a tank of water and only using half of it, which is obviously very wasteful.

[Idris]

The problem with that configuration is that the hot water flowrate out of the tap is restricted by the rate at which the boiler can heat it. A separate tank acts as a buffer and so enables hot water to be drawn off at a faster rate than it is generated (just like a normal hot water tank with immersion heater). Probably not such a big deal if everyone takes showers, but for those of us who like a good wallow in the bath, a disaster!

[motorman]

The problem with that configuration is that the hot water flowrate out of the tap is restricted by the rate at which the boiler can heat it. A separate tank acts as a buffer and so enables hot water to be drawn off at a faster rate than it is generated (just like a normal hot water tank with immersion heater). Probably not such a big deal if everyone takes showers, but for those of us who like a good wallow in the bath, a disaster!

That's correct Hugh, It does take a little longer to run a bath, but at least that way i know i have only heated the water in the bath and not left a few gallons of hot water unused in the hot water tank!

I can live with that no probs, although for speed i do use the shower more often to be honest!

[YYS4BOB]

Having worked in the gas industry for 40 years, may be I can clear this up. A Combi (combination) boiler combines central heating and instantaneous hot water functions. There is no large volume storage tank of any kind required. A sealed system, so no feed tank in the loft for the central heating circuit. 30kw is a very big boiler. I run an 18kw Worcester Greenstar Ri. This heats 11 radiators and gives great showers with no problems. It is vital that the pipework is flushed out properly before the new boiler is fitted. Your price range quoted is what I would expect. See if Power Flush is included in the price.