System or Combi boiler??

[Redlion_uk]

Dear all,

I am having a kitchen extension done so will be getting rid of our old Vaillant conventional boiler (25 years old!).

After the extension is complete we will have 3 bedrooms, a 1st floor bathroom, a ground floor shower room, and kitchen. The idea is to allow 2 people to have a shower simultaneously. At them moment, the hot water pressure is quite low especially to the first floor bathroom, where the hot water completely stops if somebody opens a tap downstairs.

I was thinking about getting either a high flow combi boiler (e.g. Vaillant ecoTEC plus 937) or a Vaillant system boiler with an unvented hot water cylinder.

Which would be the best option to go for? I checked the cold flow-rate myself and is approx 20L/min downstairs, 15L/min upstairs. The mains pipe seems to be 25mm diameter.

Any help appreciated. Many Thanks.

 

[gaspastemania]

Lose the combi get to many problems in future imo, i would go for conventional with all external controls .

 

[dontknowitall]

I'm a system boiler man as well. Biggest downside of combis is if the water's turned off from mains then you've no backup supply and have to toddle off to the local standpipe. If boiler malfunctions you can't turn on immersion heater to maintain your hot water supply. Combis and baths don't seem to be that wonderful either.

 

[Mrs Tara Plumbi]

I am a big fan of combis! But they are not for every house and in your case system is probably best.
dontknowitall makes lots of good point too.
Advantage of combi is never ending supply, unlimited supply of hot water to one tap or one shower instantly even when everything has been turned off because you've been away. no waiting 20 minutes of so for water to heat up.

 

[AWheating]

i would say either a unvented system or a combi with electric showers. those hi flow combi's are huge and you need an A/C to fit one.

 

[GasmanxxxR1]

Unvented cylinder everytime mate, Vailliant system boilers are top notch aswell

 

[nysk2008]

unvented on that system all day long

 

[woodsy]

Agree with Mrs TP, combis great in the right application but would agree that a unvented / system would be better with the senario described.

 

[Redlion_uk]

Thanks guys, I think I will be going down the unvented cylinder route. Is there any way of getting a continuous flow of hot water from these? do they refill and heat up whilst being used? I just don't want the water to keep running out if somebody decides to have a bath.

 

[dontknowitall]

Thanks guys, I think I will be going down the unvented cylinder route. Is there any way of getting a continuous flow of hot water from these? do they refill and heat up whilst being used? I just don't want the water to keep running out if somebody decides to have a bath.

Short, truthful answer, is no, in my opinion. Can get around this by heating much more hot water but will the cost of a larger cylinder and the heating of the hot water justify the expense (let alone the extra CO2 pumped into the atmosphere)?

Presumably you can do what most of us do? One has a bath/shower and the other waits for 20 minutes or so for some hot water.

 

[Ian10261]

Unvented every time if you got a good flow rate and at 20 ltrs p/m you have. Also looking at it another way, you'll be getting that 20 ltrs p/m at 60 degrees thats about 20 more than a combi so you wont be using quite so much of it with your showers, or anything else for that matter.

 

[mike_s]

Where are you based? Perhaps one of our local members could give you a quote?

 

[HHP Ed]

ever thought of having a combi with a unvented cylinder, could have the combi doing one the kitchen and ground floor shower room and smaller unvented cylinder doing the upstairs one. depends on the pressures and how good a plumber you get

 

[Redlion_uk]

I was actually thinking about a combi for the taps and the cylinder for the bath/showers. But by doing this would the central heating turn off in the cold winter when the taps are being used or the cylinder is being heated?

How exactly do the unvented cylinders work? Does water enter from the mains and then hot water from the system boiler passes through the coil to heat it up?
I'm finding it hard to find a straight forward explanation.

Thanks for the help guys.

 

[Ian10261]

The only time the heating would turn off is when you open a hot tap that is supplied by the combi directly and you would'nt even notice any effect unless you left the tap running for ages.
Unvented cylinders work in pretty much the way you describe but there are VERY important safety issues to consider and hence they must only be installed by competant persons and need to be notified to BCB.

 

[dontknowitall]

The big cylinder is a water tank.

Inside is a coil (made of copper). Have you touched a hot water copper pipe? They're hot!

Water from the boiler is heated and when heating hot water, the pipe run goes from the boiler to the cylinder, through the coil, then returns to the boiler. If the water returning to the boiler is warm enough the boiler stops heating, otherwise it continues to heat until the returning water is warm enough. The heating water (from the boiler) is kept in the coil and is totally separate from the hot water in the cylinder.

The heat from the coil transfers to the water in the cylinder and so heats up the tank of water. The immersion heater on the cylinder is a secondary form of heating the water in the cylinder and is similar to a kettle element. If the boiler stops working you can heat water via the immersion heater.

Finally, the heating circuit from the boiler is split into hot water and heating (radiators).

Hope this clears up some of the confusion!

 

[WaterTight]

you forgot to mention where the 3.6" gerberit female cranked push-fit sludge cock figures into the proceedings.

 

[Redlion_uk]

Thanks for that, a nice clear explanation.

I've decided to get the Vaillant uniSTOR 180L unvented cylinder with a ecoTEC plus system boiler.

There are several models in the range though.. which would be right for me? (9 radiators, 2 bathrooms)

• ecoTEC plus 612 - 4.9 - 12.0kW
• ecoTEC plus 615 - 4.9 - 15.0kW
• ecoTEC plus 618 - 6.7 - 18.0kW
• ecoTEC plus 624 - 8.7 - 24.0kW
• ecoTEC plus 630 - 10.0 - 30.0kW
• ecoTEC plus 637 - 12.0 - 37.0kW

Does this make sense to anyone? Does anyone here already have a vaillant system + cylinder combination? What other controls do you use?


Thanks in advance.


:smiley2:

 

[Redlion_uk]

I've had to have a rethink taking my budget into account and I have to go for a combi. Is the Vaillant combi 837 any good?

My flow rate is now 25L/min kitchen tap and 19L/min upstairs bathroom basin tap.

The old conventional boiler gives a measly 6.5L/min! Which I'm assuming is the reason why the upstairs hot water completely turns off when a downstairs tap is run.

With the new combi, will I still get some hot water upstairs? rather than a complete shut off

 

[SUSSEX MAN]

Hi I would say system as well, But i would say that you have different boilers with different kw but realistically you need someone to go around your rooms to see how many m3 in each room to get the best energy efficiency to see what boiler would be good for you

 

[metaldust9]

ad go 33 kw combi with electic shower in othershower room cos if your boiler goes down you can a least have a shower and an unvented/system boiler system would need heating up and not good for quickness unless used the night before

 

[Gray0689]

Hi I would say system as well, But i would say that you have different boilers with different kw but realistically you need someone to go around your rooms to see how many m3 in each room to get the best energy efficiency to see what boiler would be good for you

Agree
It's not a matter of just guessing what size you need has to be calculated