If you think a combi is going to satisfy two outlets at once you are sadly mistaken.
Inherent fault with combi boilers?
- Thread starter johnkirk
- Start date
If you think a combi is going to satisfy two outlets at once you are sadly mistaken.
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A
ALEC1
combis on more than one hot tap are always a disaster unless the incoming flow is sufficient AND the taps are ALL flow regulated...
Even so filling a bath is going to hog most of the hot water leaving you disappointed!
If you really need to satisfy such hot water demand then a storage combi is the way to go..such as a viessmann 222 19kw , glow-worm ultra power... both have a sensible heat out put for what is a very small heat load
Even so filling a bath is going to hog most of the hot water leaving you disappointed!
If you really need to satisfy such hot water demand then a storage combi is the way to go..such as a viessmann 222 19kw , glow-worm ultra power... both have a sensible heat out put for what is a very small heat load
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The Vaillant 937 may do the job better for you as it has a built in store of hot water that allows 'instant' flow of hot water whilst the boiler fires up and allows very low draw off flows before the boiler fires.
It is also claimed to provide 'hot' water for ages due to a combination of the store and direct combi flow.
(Trigger disbelievers now!
)
I know it works well because I have one and will be installing a second at my latest house renovation.
BTW 2 showers works on a Vaillant 831 but is dependent on matched flow rates of the shower heads and equalised plumbing pipe lengths/pressure losses.
It is also claimed to provide 'hot' water for ages due to a combination of the store and direct combi flow.
(Trigger disbelievers now!
)I know it works well because I have one and will be installing a second at my latest house renovation.
BTW 2 showers works on a Vaillant 831 but is dependent on matched flow rates of the shower heads and equalised plumbing pipe lengths/pressure losses.
A
ALEC1
the 937 needs a thermostatic mixing valve to get the optimum performance, but its a good boiler... still have to upgrade the gas pipe though!
What's the dynamic pressure, i.e when the water is flowing?
If you have a garden tap, turn the cold tap in the kitchen full on and then turn the garden tap full on and see what effect it has on the kitchen flow. This simulates two outlets running at the same time, e.g. a shower and a toilet filling up.
You should also use the Whole House Boiler Size Calculator to find out what the heating requirement is for your house. You will probably find that this is below the minimum output of the boiler. A regular problem with combi boilers and something which few manufacturers have taken into account.
Thanks Tipper, I will look into this, given there is no space for a Megaflo (or equivalent).
Very useful link, thanks D Hailsham! It comes out at around 12.5 kW.
And now, just as an aside:
In my own house (4 bedrooms, 3 bathrooms) I've still retained my faithful Potterton Netaheat Profile 50e boiler, with separate HW cylinder. The boiler is 23 years old, has never been serviced nor ever needed repair, and is very silent and works perfectly. No banging, hissing, cold spots, etc ...! No power flushing ever, nor magnetic filter, and due to my own neglect inhibitor has never been added, nor after draining the system after adding new radiators, etc. I was very nearly persuaded to upgrade (?!) the boiler 18 months ago when we had our loft conversion done, believing that because a new boiler would be 90% efficient, whereas my current one only 65% efficient, that it therefore made economical sense to scrap it. All the energy efficiency institutions and literature want you to know how much fuel you could SAVE by replacing your old boiler, but never seem to factor in the additional costs you will pay that may more than wipe out any fuel savings!
I've now decided to retain my old boiler till it bites the dust for the following reasons:
° Current boilers last only 10 - 15 yrs (including WB and Vaillant brands). There's a fair chance my current boiler will last a further 23 years!
° Brochure stated efficiencies of around 90% are significantly higher than the figure you will achieve in practice
° Although my current boiler is quoted as being only 65% efficient, in practice it is higher, since this figure assumes the heat from the boiler casing is wasted. But since the boiler is wall mounted in the kitchen, the boiler itself acts like a mini radiator, so this heat is not wasted (except for the relatively small amount in summer when the boiler is heating the HW and no space heating is wanted in the kitchen). Further, it has no pilot light so no wasted gas from this.
° I save on installation costs involved with installing a new boiler. Yes, there is obviously the risk the old boiler can pack up anytime, but I've been told by two separate CH installers to expect my current boiler to last a further 23 years, given the superior construction of the heat exchanger compared to current ones.
I think that you are over rating your Netaheat.
Even if the 65% is the seasonal efficiency that's based on the boiler being brand new. At this age that figure is probably considerably lower!
Furthermore, many parts of the Netaheat are no longer available! I keep a few for my customers as I enjoy the challenge of keeping old boilers going but the economics are not encouraging in properties where the gas consumption is significant.
Tony
Even if the 65% is the seasonal efficiency that's based on the boiler being brand new. At this age that figure is probably considerably lower!
Furthermore, many parts of the Netaheat are no longer available! I keep a few for my customers as I enjoy the challenge of keeping old boilers going but the economics are not encouraging in properties where the gas consumption is significant.
Tony
Every month it continues to give me faithful service is a bonus, until the day it bites the dust. I'm not suggesting paying to repair it in the event it fails, but in the meantime, and based on overall costs I believe I'm benefiting from net savings by not replacing it.
A new boiler could save about 40% of your gas bill !
If your annual gas bill is say £1500 then that could be £600 per annum.
With interest rates very low a simple calculation will probably show that the longer you procrastinate as gas prices increase the more you are losing.
I would expect that using a good boiler like an Intergas the cost would only be about £1600 plus extra if you need to upgrade the cylinder which if old could be losing £200 p.a. in heat losses.
Tony
If your annual gas bill is say £1500 then that could be £600 per annum.
With interest rates very low a simple calculation will probably show that the longer you procrastinate as gas prices increase the more you are losing.
I would expect that using a good boiler like an Intergas the cost would only be about £1600 plus extra if you need to upgrade the cylinder which if old could be losing £200 p.a. in heat losses.
Tony
40% might be a tad ambitious. I am happy to tell customers 20 ish % and anything more is a bonus.
You need to be very aware of the current boiler.
Old cast iron lumps like the Netaheat will lose a lot of heat when cycling.
A low water content fan flued boiler like a Vokera 20-80 are already pretty efficient and savings are unlikely to be much more than about 12% at best.
Further problem that a boiler like the Intergas will have lower savings if the DHW preheat is enabled which is largely needed because of the long delivery delay otherwise. Using the timed facility will be less wasteful.
Tony
Old cast iron lumps like the Netaheat will lose a lot of heat when cycling.
A low water content fan flued boiler like a Vokera 20-80 are already pretty efficient and savings are unlikely to be much more than about 12% at best.
Further problem that a boiler like the Intergas will have lower savings if the DHW preheat is enabled which is largely needed because of the long delivery delay otherwise. Using the timed facility will be less wasteful.
Tony
When I changed from an old iron Flamingo to a Vitodens the annual usage dropped from 1570, 1463, 1807, 1722, varying with severity of winter, to 1083, 1051, 1238, 1170 cu m
However last winter was long and cold and it went up to 1345
1807 was the 2005/6 cold year, so 1345 is about a 25% saving which I find satisfactory. A mild winter was 1463 cf 1051 about 30% saving.
ther are other variables like I changed the TRVs and more occupancy now so very difficult to get a true saving figure.
However last winter was long and cold and it went up to 1345
1807 was the 2005/6 cold year, so 1345 is about a 25% saving which I find satisfactory. A mild winter was 1463 cf 1051 about 30% saving.
ther are other variables like I changed the TRVs and more occupancy now so very difficult to get a true saving figure.
A
ALEC1
thats weather compensated and from a cast iron open flue boiler to a viessmann vitodens 200
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