Combi Boiler

[robj20]

I've not seen a cost break-down of the wasted energy/resources in purely-combi setups,
via a permanently on pre-heat mechanism or wasted water and energy meeting occasional demands, but, compared to joint combi/pressurized-hot-tank solution I had in last property, every time I use the dam system it's the main thought.
....Have an Ideal combi.

We went combi purely to save space, and instant unlimited hot water.
I went with an Ideal Vogue Gen 2. I really liked the screen on the boiler, no codes if anything goes wrong it tells you properly whats wrong and how to fix it.
The guy fitting it loved it as well as the screen gives him all the data he needed for commissioning and servicing. Gives you nice graphs showing everything.

 

[peige]

I've Bosch in the last two houses and they have been faultless but would also look at Vaillant now too.

I have the same issue coming in the summer, all being well the current boiler will get us through the winter but its 25 years old although regularly serviced by BG who have pretty much replaced everything over the years bar the heat exchanger.
Only drawback for a combi for me is the way that showers are badly affected by other water use in the house, so if somebody flushes the toilet the shower dies away (assuming thermostatic shower controller) or worse goes hot if its a standard one. We had to make sure the washing machine wasn't running if you wanted a shower or it could be traumatic! Consequently thinking of going for pressurised hot water heated by a gas boiler. Plumber I talked to tells me it will more or less double the cost over a standard combi setup but will do what I want, i'm told that they do this kind of setup on large houses with many bathrooms. Living with basically 5 adults in my home I still see it as worthwhile though.

 

[jpaul]

and instant unlimited hot water.

the problem is it's not instant
... (layout specific but) with combi near kitchen, as opposed to a tank near bathroom, just a waste of water/energy firing up boiler to wash your hands, say.
- previous thread on the delay

 

[£15]

You can get combi boilers with internal storage. Obviously they're not as big as regular tanks, but may be enough to meet an individual's demand for instant hot water.

My boiler is in the kitchen and it can take a while to get hot water in the bathroom. But if I had a hot water tank upstairs then it would takes ages to get hot water in the kitchen.

I got a new boiler last week, replacing 25kw Vokera for a Worcester 34cdi. Very happy with it. A lot quieter and quicker to supply hot water. I've taken meter reads and will be interested to see how it works out economy wise over the next few years.

I would have liked one with an internal tank, but the quote was getting higher and higher and I had to draw a line somewhere.

 

[robj20]

the problem is it's not instant
... (layout specific but) with combi near kitchen, as opposed to a tank near bathroom, just a waste of water/energy firing up boiler to wash your hands, say.
- previous thread on the delay

Okay not instant, within 5 seconds.
It's no more wasteful than a system at providing hot water to taps. I'd argue its more wasteful in a system.

 

[jpaul]

Can't find any online calculations ... but these seem a good idea https://lowenergysupermarket.com/water-heating/water-services/1304/combisave-les
are there combis with such a mechanism built in ?

Even brand new A-rated boilers are not as efficient as you may think. Every time you turn on your hot water tap you are wasting water, gas, time and money. This British innovation is a thermostatically operated valve that can be fitted to the majority of new and existing wall hung Combi boilers

How does it work?
By controlling the water flow to the hot taps during the initial boiler firing process, the Combi boiler can accelerate the heating of hot water and reduces the amount of fuel needed. When the hot tap is turned on, the CombiSAVE reduces the flow of water until it has reached a set temperature. At this point, the valve opens fully and allows the hot water to flow at full delivery capacity through your domestic system. The CombiSAVE will save you an average of 6 litres of water every time the hot tap is turned on from cold. This will vary depending on your local water pressure.

 

[Buffman]

Can't find any online calculations ... but these seem a good idea https://lowenergysupermarket.com/water-heating/water-services/1304/combisave-les
are there combis with such a mechanism built in ?

Not sure on if combis offer this (mine doesn't) but 6l of water is incredibly cheap. Even if on a metered supply I think it's about 14pence for 1000l of water.

 

[robj20]

What i did was run the hot water from the boiler to the kitchen tap in 8mm pipe vastly reduces the amount of time it takes. Bathroom has 15mm up to the shower and bath then an 8mm tee to the sink.

 

[Sasahara]

Not sure on if combis offer this (mine doesn't) but 6l of water is incredibly cheap. Even if on a metered supply I think it's about 14pence for 1000l of water.

Water isn't that cheap, it's around £3 for a 1000 liters. Including waste water charges.

 

[bowey]

I put an ideal logic in my house, been spot on for 5 years.

My friend who mainly installs combi boilers has started fitting a lot of "alpha" combis he said they are really good, it depends on whoever is installing it, I think most of the common ones are a near enough copy of each other so they are all pretty good.

 

[jpaul]

Water isn't that cheap, it's around £3 for a 1000 liters. Including waste water charges.

indeed .. this guys done the calculations for showers / baths the water costs more than the gas to heat it - hadn't thought of that.
https://energy-surprises.blogspot.com/2015/07/how-much-does-your-bath-or-shower-cost.html

but moreover, his calculation on combi vs tank https://energy-surprises.blogspot.com/2012/10/combi-boiler-versus-hot-water-tank.html
- based on a 2 person 1300kw/pa water heating
- the combi looses are 500kw/pa (40% down the drain ) and the tank 370Kw/pa - so 130kw/pa win for tank (seemingly only £4 pa ???)
- combi users use 20% more water, that would save significantly more than £4 (per month) with tank

so it would take a while to payback the additional cost of a tank.

... etc
Combi loss
Every time you turn on the hot tap the boiler has to start the burners going and warm up the heat exchangers so that the water is heated properly. Then when you turn the tap off it takes a moment for the boiler to notice this and to shut off. It clears out the hot gas from the combustion chamber (for safety reasons) and the heat exchanger cools down. Some boilers are better at this than others but in the absence of specific test data SAP assumes combi loss comes to 600 kWh/year. In practice it will depend on how often you turn the taps on and off.

 

[robj20]

Even more so for me with unlimited water. Lol

 

[jpaul]

... even with 'unlimited' water, the other issue is that you have to wait for the shower to be ready for you / up to temp,
which I would place at nearly a minute, playing the water on your feet.

problem is that new builds are putting in combis, and there would be no place for an after market tank version.
with older houses, with that airing cupboard/plumbing then the premium for a tank install is reduced - break even over 10 years?
and you have it's convenience, in the interim.

 

[robj20]

... even with 'unlimited' water, the other issue is that you have to wait for the shower to be ready for you / up to temp,
which I would place at nearly a minute, playing the water on your feet.

problem is that new builds are putting in combis, and there would be no place for an after market tank version.
with older houses, with that airing cupboard/plumbing then the premium for a tank install is reduced - break even over 10 years?
and you have it's convenience, in the interim.

Nope switch the shower on in the bathroom or bedroom get undressed, it warms it's self up and alerts you when it's ready. Zero waiting around.

Even without that feature no real in the house had to wait anywhere near a minute for 52c water. At most it's 20 seconds.

If you design your whole system around the combis function it isn't an issue.
We had a system before that took longer to get hot water to the taps than the combi does.

 

[mattyg]

Heat only boiler, Water tank and secondary HW supply. Instant hot water anywhere in the house. The only downside is sometimes the cold water is warm'ish

 

[Syla5]

... even with 'unlimited' water, the other issue is that you have to wait for the shower to be ready for you / up to temp,
which I would place at nearly a minute, playing the water on your feet.

My combi has hotwater to the shower in the first 5-10seconds. We do have the benefit of the boiler being in the bathroom. Our kitchen at the furthest end of the house takes about 30 seconds for the hot water to come through, but that's only if we need more then the auxiliary amount the boiler keeps pre-heated, which is enough for washing hands quickly for example and is instant.

 

[beachBOYken]

Small update, had some quotes.

Looking like it will be a Vaillant EcoTec plus 32kw or Ideal Vogue Max 32kw.

Has anyone experience with the Ideal Vogue Max?

This was actually recommended by one of the plumbers when getting a quote, I know they had some reliability issues a while back but apparently they have improved a lot recently and this Vogue Max is supposed to be a very good boiler.

 

[Syla5]

Small update, had some quotes.

Looking like it will be a Vaillant EcoTec plus 32kw or Ideal Vogue Max 32kw.

Has anyone experience with the Ideal Vogue Max?

This was actually recommended by one of the plumbers when getting a quote, I know they had some reliability issues a while back but apparently they have improved a lot recently and this Vogue Max is supposed to be a very good boiler.

as long as it has a long warranty, it is fitted correctly (ie as per the installation manual), and you stick to the service schedule during the warranty period then you should be fine. The Valliant's have a long warranty don't they?

 

[Psycho Sonny]

Last 2 properties 10y+ I've had Bosch, no issues. Just make sure they are serviced annually to maintain warranty.

arggh

paying £150 a year to service a boiler worth £1500.

after 10 years you could have just bought a brand new boiler.

 

[robj20]

Small update, had some quotes.

Looking like it will be a Vaillant EcoTec plus 32kw or Ideal Vogue Max 32kw.

Has anyone experience with the Ideal Vogue Max?

This was actually recommended by one of the plumbers when getting a quote, I know they had some reliability issues a while back but apparently they have improved a lot recently and this Vogue Max is supposed to be a very good boiler.

I have one, been faultless. Deciding factors for me were its high modulation and Opentherm support built in.