need advice on fitting combi boiler

I think that at either of those cryogenic temperatures the legionella would be well frozen !
If your airing cupboard has gone down to -253.15 degrees Celcius, I'd say you have bigger fish to fry than worry about your bath or the presence of bacteria.
 
Sponsored Links
So the statement was correct then, a combi is better for a shower, not as good for filling a bath.
Like I said, I don't know anyone waiting 4-5 minutes for the cylinder to fill the bath. If you are not waiting for it, it makes no difference whatsover whether you are not waiting 4 minutes or not waiting 8 minutes; either way you are not waiting and in both cases you come back once or twice to check the level.
 
Personally, would I remove a cylinder and fit a combi ? No flipping chance !

Slow (but getting better) hot water supply, needs a boiler that's hugely overcapacity when not providing hot water (ie in my flat, nearly 30kW to give **** poor dribble, min ranging 9kW - heating demand only about 2kW), unreliable, and you lose your hot water upstairs if someone turns on a tap elsewhere.

WHEN the boiler breaks down, you're left with not just no heating, but no hot water either. This is not IF, it really is WHEN - even if you pick the most reliable makes.
With hot cylinder - when boiler breaks down, switch on immersion heater and carry on.
 
Thanks folks,

Legionella is not a concern, more worried about hypothermia here in Scotland ha ha..yes, seems like I need to over spec a combi to heat the house, run showers and baths.
According to worcester web site my 3 bed 1 bathroom house only needs their greenstar 24 i junior...will that be good enough ? or g spend more and spec up?

cheers
 
Sponsored Links
Combi is very rarely specced on heating requirements, but on dhw demand.
24 kw is rather minimalist, and personaly, I don't rate any WB apart from the cdi. i-series are budget boilers and junior i-series are even worse. Not particularly cheap either.
CDI is a decent boiler, but way overpriced. I never recommend anything under about 30 kW for a combi and if there is any chance of a second shower at some point, I'd go even higher.
I ditched WB completely in favour of Viessmann 100 series a couple of years ago; better boiler and better price.
 
Like I said, I don't know anyone waiting 4-5 minutes for the cylinder to fill the bath. If you are not waiting for it, it makes no difference whatsover whether you are not waiting 4 minutes or not waiting 8 minutes; either way you are not waiting and in both cases you come back once or twice to check the level.

I seem to recall when I was a student or living in bedsit houses, if you left a bath running then someone else would be in it when you returned!

But they were all tank fed and if you did not get back by 6.30 pm then the water would have run cold.
 
I would keep the cylinder if in good nick and just change the boiler for another o/vent, less work for you and the installer , and as been said before when the boiler breaks down you will have hot water and sometimes you can wait 3-5 days form a engineer to come out
 
and a o/vent boiler will be cheaper to buy as there in no pump diverter e.t.c inside the boiler its all next to your cylinder
 
According to worcester web site my 3 bed 1 bathroom house only needs their greenstar 24 i junior...will that be good enough ? or g spend more and spec up?

cheers

personally would not fit a junior, they have been critised on here many times, no where near as many as Ideal but still not that highly thought of! i've fitted a few Ri's and they seem to be ok. or look at main, baxi, potterton for good mid range boilers.
 
Hi,

Been thinking about this and want some opinions please.
I currently have an old baxi gas boiler with copper cylinder upstairs, I was thinking of replacine all with a new combi boiler which involves a lot of system changes....or should I just update with a new gas boiler...simpler, cheaper to replace and much more efficient I guess ?
Just not sure...
It does mean having to heat more water than needed but if I insulate the cylinder well...maybe ok ?
I just had another thought...what about using an electric immersion heater and the gas boiler just for heating only ?
Is is cheaper to heat with electric or use the gas for all (as I do at moment)

Cheers
 
Been thinking about this and want some opinions please.
You don't have to ask for opinions here - you'll get them whether you want them or not :LOL:
I currently have an old baxi gas boiler with copper cylinder upstairs, I was thinking of replacine all with a new combi boiler which involves a lot of system changes....or should I just update with a new gas boiler...simpler, cheaper to replace and much more efficient I guess ?
Just not sure...
It does mean having to heat more water than needed but if I insulate the cylinder well...maybe ok ?
OK, just to make one thing perfectly clear, in the long term you do not heat more water than you use. It is true that you are heating a large cylinder from which you might only draw small amounts, but you only have to heat the small quantity of water which replaces what you've drawn off. Thus, if you had (say) a 100 gallon tank, and drew off (say) 10 gallons of hot water - you'd only need to supply enough heat to heat up 10 gallons of water. Many a time I've come across people who are convinced that you are heating 100 gallons from cold each time :rolleyes:

So having go that out of the way, the "cost" of storing your hot water is down to how much heat it loses - or the "standing losses". This is down to how hot you keep it, and how good the insulation is - don't heat it hotter than you need, and have good insulation, and the standing losses will be quite low.

Also, for most people this isn't "wasted heat" for most of the time. Assuming the DHW cylinder is inside the property, then the heat that does leak out goes towards heating the house - so is only wasted during those times when you've got the windows open to cool down in summer.

Against that, don't believe anyone that tells you a combi doesn't have standing losses. Many of them have some form of "keep warm" function - either they fire up from time to time to keep the heat exchanger hot, or they have a small hot water tank that they keep warm. Without this, it's normal to get a delay (sometimes considerable - I've measured a whole minute on a not that old combi !) between turning on the hot tap and getting hot water out of it. With either function, there's a heat input required in order to keep things hot.

In favour of keeping the hot water cylinder :
You've got stored hot water, so the only delay when you turn on teh tap is down to the length of pipe and the time needed to flush the cold water through.
You've got a backup, so you can switch on the immersion heater when the boiler breaks down - which it will !
Because you've a much simpler boiler (there's a lot of complexity in a combi) then it should break down considerably less often.
You can size the boiler properly according to the heating load for the property.

The downside (which doesn't bother a lot of folks) is that your hot water is at low pressure - whilst a combi does mains pressure hot water (as does a thermal store).

A combi is complicated and will break down more often.
When it breaks down, you've have no hot water.
Because it has to have a huge capacity in order to provide a decent flow rate at decent temperature, it will be oversized for the heating load in most properties (which is inefficient) - however modern boilers are getting better and better about how low they can turn the burner down.

And the biggie - because they have limited flow rates, you can have a situation where an upstairs shower will stop completely if someone turns of a tap downstairs.

Developers love combis because it means they can build a rabbit hutch about 1m^2 smaller by leaving out a DHW cylinder. And because there's less plumbing, they can knock a few hundred quid off the build cost.

Personally, since you already have a DHW cylinder - I'd say keep it and stick with a heat only boiler.
I just had another thought...what about using an electric immersion heater and the gas boiler just for heating only ?
Is is cheaper to heat with electric or use the gas for all (as I do at moment)
From memory, gas is about 1/4 the cost of electricity, and still about 1/2 the cost vs a "cheap night rate" sort of tariff.
 
Thank you for your time and thoughts, I think I am tempted to stay with my system as it is and just replace the old Baxi gas boiler for a more efficient one.
One thing, all my water is heated via the gas, the copper cylinder is heated by the Baxi, not electric immersion.
That is why I was asking...is it worth considering to use electric to heat the water, I see you say electric is more expensive...so myabe I will stick with my all gas system then.
Do you think I will save on the gas with a new boiler? is it worth the expense to change it? The baxi works well enough I am just not sure it is as efficient as a modern one.
Thanks again and to everyone on this forum, really so helpful :)
 
One thing, all my water is heated via the gas, the copper cylinder is heated by the Baxi, not electric immersion.
Yes, I figured that - it's an extremely common setup, and the immersion heater gives you that backup option for when teh boiler breaks down.
That is why I was asking...is it worth considering to use electric to heat the water, I see you say electric is more expensive...so myabe I will stick with my all gas system then.
Yes, stick with gas, electric is a lot more (at the moment)
Do you think I will save on the gas with a new boiler? is it worth the expense to change it? The baxi works well enough I am just not sure it is as efficient as a modern one.
That's a tricky one.

Your old one (assuming it's non-condensing) is probably (from tidbits I've picked up in here) about 70% efficient. A new one will be rated at 90+% though that assumes a regime where it's condensing - otherwise efficiency drops somewhat. So a new boiler should cut your fuel bills by around 20 to 25%. So in purely financial terms, work out how long it'll take to pay for a new boiler.

Against that, you can assume that the new boiler won't be as reliable or last as long as an old one (in general - some are better than others) and when it does break down will cost more to fix (they are more complicated, even for a heat-only boiler).

And if you are so inclined, fitting a new higher efficiency boiler might give you that warm fuzzy feeling that you're pouring less CO2 into the atmosphere.
 
Thank you for your time and thoughts, I think I am tempted to stay with my system as it is and just replace the old Baxi gas boiler for a more efficient one.
One thing, all my water is heated via the gas, the copper cylinder is heated by the Baxi, not electric immersion.
That is why I was asking...is it worth considering to use electric to heat the water, I see you say electric is more expensive...so myabe I will stick with my all gas system then.
Do you think I will save on the gas with a new boiler? is it worth the expense to change it? The baxi works well enough I am just not sure it is as efficient as a modern one.
Thanks again and to everyone on this forum, really so helpful :)


Hi,

This might also help but the Goverment are running a boiler scrappage scheme and your back boiler will qualify for a £400 voucher from them.

You will need to get a quote from a Gas Safe company but any gas safe registered installer can then install the boiler and sign the voucher.

I see you are from Midlothian, if you are unsure about anything or need any advice PM me. I live near Penicuik and we cover Edinburgh and the Lothians and could offer you free advice.

Cheers
 
Damn you scots...the one scheme that was worth funding and the government both under funded and time limited it.

Make the most of it!
 

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.


Are you a trade or supplier? You can create your listing free at DIYnot Local

 
Sponsored Links
Back
Top