using a combi for a unvented system (megaflow cylinder)

[normbeef]

Hello Plumbers..

I am living in a house that has a newish (2 years old) Worcester Bosch Combi boiler..

We are knocking the place down and I want to install a new Megoflow unvented tank system into the new house. So my question is can the combi be used for this purpose ?

It seems a shame to get rid of it as its almost brand new !!

the new system will have underfoor heating on the ground floor, and rads upstairs, I will also want a separate motorised valve for a couple of towel rads...

 

[aggis]

.Go for it, if fitted in a laundry just supply the sink off the combi side, as long as the cold is connected through the boiler, it doesn't matter if you run the tap or not

 

[bengasman]

No problem for the unvented cylinder and ufh.
A separate zone for a couple of towel rails is not a good idea; it will leave the boiler cycling and running uneconomically.

 

[normbeef]

Wow.. thanks for the swift reply..

So to sum up...

The cold mains will feed into the boiler - the main flow / return from the boiler will go into the Megaflow tank.

On the tank there will be 3 motorised valves, 1 for hot water (regularised) 1 for the central heating (including the underfloor heating) 1 for the towel rads..

or would is it advisable to change from the towel rad circuit to separate the ground floor underfloor heating and the upstairs rads.

cheers

 

[bengasman]

I do hope you are not planning on doing this yourself.

 

[diamondgas]

Hi Normbeef. If your knocking down and building new you may have to fit a new flue to the boiler if the wall thicknesses are different! I don't think you need to run cold to the boiler or hot from it unless it has a built in pre-heat for the domestic. that is unless it's needed for a filling loop. You can always fit that alongside the megaflow if need be...

I believe new build has to have separate zoning upstairs and down ...

 

[normbeef]

dont worry plumbers I am not doing it myself... I might run the pipes in for the rad's but thats about it...

I work in IT infrastructure and I wouldnt expect a plumber to do what I do either.. I just wanted to get an idea if the combi could be used without speaking with a plumber who is after supplying a new boiler without the need..

 

[bengasman]

.... I just wanted to get an idea if the combi could be used without speaking with a plumber who is after supplying a new boiler without the need..

It might be more productive to find a good and trustworthy plumber, than trying to learn about the subject via email hoping you will be able to catch him out if he tries to pull a fast one.
It would be the same as trying to understand enough about networks myself in the hopes of winning an argument with a network engineer; I'd look like a right prat.

 

[normbeef]

It might be more productive to find a good and trustworthy plumber, than trying to learn about the subject via email hoping you will be able to catch him out if he tries to pull a fast one.
It would be the same as trying to understand enough about networks myself in the hopes of winning an argument with a network engineer; I'd look like a right prat.

yep your probably right... thing is I only really wanted to see if it were technically possible to use the combi in that type of system, thats why i came onto the forum because as in my everyday job I can get lots of opinions from skilled people who know what they are talking about.

i aint trying to catch anyone out, i just need to be a bit more informed about my choices, I had a megaflow tank installed in my last house and it was superb, I just want to follow the same design again but using the combi instead ...

 

[bengasman]

Just remember that there are a lot of factors that determine whether you actually get the maximum out of your cylinder.

Mains pressure; determined by supplier
Mains flow; weakest link in chain principle. Under ground mains should be 25 or more from streetvalve to cylinder and bath(s); one metre of 15 mm, and the whole performance will be drastically reduced.
Cylinder needs to be big enough.
Timing for dhw and ch should be totally independent and never at the same time.
Ch and dhw need both to be balanced properly.

Then there is more, AND it all needs to work together. Far more than any house holder could ever keep an eye on.

 

[normbeef]

I havent got a pressure rating but luckily the mains are quite strong where I live, and as for keeping an eye on it.. no thanks I just want a nice hot shower without the missus turning on the tap and changing the pressure or the temperature..

 

[SafeGasInstall]

then dont get involve with putting pipe work down ,leave it to the pro 🙂
it will work with combi but will be much better with system boiler imho

 

[bengasman]

it will work with combi but will be much better with system boiler imho

Do you mean the megaflo would work better with a system boiler?

 

[SafeGasInstall]

no,as you can have kitchen sink of the combi and then bathroom from the UHWC ,and shower from combi !

it just complicates it ,I like things simple !

mains is to UHWC balanced hot and cold to all point of use , immersion for back up ! s plan for hot water and ch and if want like this op tower rails on another one then will suggest electrical ones !!!

sorry just like it simple !

 

[mfgs]

A combi boiler is just a system boiler with the capacity to also provide instantaneous hot water. It wont work any better with a system boiler than a combi, it will work exactly the same. Infact the combi is better because you can provide instant hot water for the nearest outlets. Airing cupboard to kitchen sink can be quite a long run in some houses, but if the combi is in the kitchen then it will give you hot water quicker.

 

[diamondgas]

You can just use the combi as a system boiler and forget about the instant hot water side ... As Said before, providing there is no a pre-heat. The answer to 'normbeef' is yes it is possible to re-use a combi as a system only boiler. Certain factors need to be taken into account. Does it have Pre-heat and can it be disabled?Is there availability of replacement flueing? And what, if any, guarantee would you give? I think the latter would dissuade me from undertaking the re-fit. What difference does a £700-£800 boiler make to a whole house re-build? Very little, probably less than 1% of the cost ... Why even consider it? IMHO