System boiler + unvented cylinder or highflow combi for large house with big showers

[JPBuckley]

Hello
I'm new to the forum and wondered if anyone could give me some first hand experience of the Worcester 550cdi combi boiler? We are planning to combine the two systems we currently have into one (the existing boilers are 20years old plus we need to add more radiators, so it seems sensible to do everything at once before something goes wrong).

I've seen some posts suggesting that with the highflow combis you do achieve very good flow rate so long as the small-ish storage tank is not depleted. After that, the flow rate drops. The installer I've spoken to denies this however and says you'll get 25l a minute whatever, even if 2 showers are running at the same time (quite often this is the case in our house). Can someone tell me their experience please?

We have 7 bedrooms plus 2 bathrooms with (currently pumped) rainforest showers - just one bath - a family of 4, although there are often guests. We're going to have 20 radiators overall as its cold where we live. The mains pressure has been tested and is good (3bar). We havent had the flow rate tested though.

Is it safer to go for a system boiler (we're recommended the WB 40cdi) plus unvented cylinder (250l)? We just dont want any disappointment after a costly investment. Running cost is a big issue too - we're hoping to reduce the pretty massive bills we have on running our two systems at the moment.

Any insights greatly appreciated!

 

[SimonJohns]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

biggest uvhws you can fit with system boiler sized correctly

combi is a waste of money and will be inadequate in this situation

edit : modern boilers and cylinders are all highly efficient

i would say worcester, but gasman will be along soon and recommend a baxi lol

 

[marleyco]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Just fitted a keston 55 kw and 300 ltr unvented today, as architect specified. To cope with a very large 6 bedroom, 3 bathroom house. plus utility, cloakroom and kitchen, its not far from what your describing. I feel the boiler might be slightly over sized, but on the whole a good system that should just about cope. Most important, pressure and flow on any system you choose must be good enough to meet your usage. No domestic system will be perfect but I think the one I mentioned will suit you better.

 

[JPBuckley]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Thanks very much both - I'm feeling that the combi may just be a bit risky. I havent looked at keston but will investigate. Thanks again.

 

[SimonJohns]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

kestons arnt known for their reliability

 

[Mbear]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Just fitted a keston 55 kw and 300 ltr unvented today, as architect specified. To cope with a very large 6 bedroom, 3 bathroom house. plus utility, cloakroom and kitchen, its not far from what your describing. I feel the boiler might be slightly over sized, but on the whole a good system that should just about cope. Most important, pressure and flow on any system you choose must be good enough to meet your usage. No domestic system will be perfect but I think the one I mentioned will suit you better.

Stop keeping Keston in business !!!! Lol

 

[marleyco]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

The keston was specified as said, as the kw of 55 was needed, at that size its classed as commercial, worcester do one as does vaillant, names you will be familiar with. I'd go with one of those if it were my choice.

 

[Mbear]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Don't buy a high flow, they're unreliable, far too many moving parts.

Youd be best of with a high kw heat only boiler with a 300litre uv cyl or maybe bigger if reqd.

The high flow style of boilers are not great

 

[JPBuckley]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Thanks very much - so not much support for the highflow combi. I think we'll steer clear of that then.

 

[Mbear]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Thanks very much - so not much support for the highflow combi. I think we'll steer clear of that then.

Add Keston to that list

 

[SimonJohns]

Add Keston to that list

And ferroli
Lamborghini
Heat line
Ideal
Many more

 

[Mbear]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

And ferroli
Lamborghini
Heat line
Ideal
Many more

Even vokera these days

 

[Mbear]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Basically you need hot water and good heating whenever you need. Vaillant , Worchester or keston are BMW or MERCEDES as you need the service every years and when these boilers change their mind, then will ask you to spend a good money on parts.
I recommend Baxi Main as its quit simple boiler and not much electronic. This is the reason your 20 years old boiler still working

Keston are not BMW or Mercedes, more like Russian skoda

 

[tamz]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

A 550 highflow only has 30kw for heating and 40kw for hw. The heating output may be more of an issue than the hw output.
The heat bank is around 50 litres and it can replenish around 15 litres/min so if you were drawing 20 litres/min you would get around 10 mins at the full rate then you are running in combi mode at 15 lpm forever if you like.
Compare this to a 210 litre hw cylinder and you would get around 10 minutes then cold.
This is a very rough example as the running times would be longer and i can't be bothered to work it out.
Both have their advantages and disadvantages.
I had a highflow 400 in my last house and could run a shower with body jets on for full pelt for around half an hour before it cut back to combi mode.

 

[Howsie]

Change your installer.

Sent from my GT-I9100 using Tapatalk

 

[What boiler]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

Did you ever get an answer, i also have the same situation

 

[Howsie]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

I think is was answered many times over.

 

[PlumbBobBob]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

I think is was answered many times over.

i agree. do a search on the forums you will find quite a few posts on this subject.

 

[Andrew Davis]

Re: System boiler + unvented cylinder or highflow combi for large house with big show

You want to avoid a long pipe run full of hot water. You previous had two boilers, I wondered if you the bathrooms and other outlets were on a long run?
Will you get an adequate flow to run hot water to the furthest radiator from one boiler?