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Good afternoon,

We are looking to change our existing system (boiler, cylinder and massive water tank in the loft) and have been advised on a Megaflow and a Combi boiler from different plumbers.

I am really keen on a combi boiler (water on demand, no tanks etc), though understood they were best suited for smaller properties. The plumber suggested a 42kw combi, which would be capable of feeding 2 showers at the same time and can comfortably deal with the central heating (15 average sized rads - albeit not at the same time).

We currently have a 15mm mains water pipe which I will be looking to upgrade to 25 or 32 as both plumbers suggested this regardless of which system I went for.

Its a relatively large 5 bedroom house, however it is just me and my girlfriend, although we do plan to have kids in the next few years. Its very unlikely two showers will regularly be used at once and I haven't had a bath in about 15 years.

The house has been extended over the years (before we moved in) so the current system is a mess with bits tagged on all over the place - I was hoping with a combi, it would be simpler and easy to maintain with fewer pipes, tanks etc getting in the way.

Any thoughts would be appreciated.

Thanks
Chris
 
If your planning on running more that one outlet at the same time at minimum I would suggest a storage combi e.g. Viessmann 222

But your better going with an unvented cylinder and heat only boiler

But as you've already said water main is key, I would be looking at minimum to feed two outlets 3 bar and 25-30lpm
 
As above ^^^ a combi is not a good idea in a 5 bed house . The boiler / system should be sized to the house not the occupants , however it is your house and you can fit whatever you want .
A heat only/ system boiler and a unvented ( pressurised cylinder) would be best in my opinion
 
If you have the space and money get an unvented cylinder.
If not and you can live with the limitation on hot water produced go for a combi.
 
Thanks for your reply.

What would the limitations be? The 42kw boiler could service two showers at the same time, and we would have unlimited hot water on demand with no requirements for any tanks. The only limitation I see is not being able to run a bath/shower at the same time as having the central heating on?

The house has one bathroom, one en-suite and a downstairs cloak.
 
In the middle of winter your stuck with two ok ish showers at the same time or one great one but both won't have heating at the same time
 
The limitations are how many litres of hot water can be produced per minute - which is fine if you can stagger showers etc.
And also there is no immersion heater backup
 
Your house your choice bud , i would personally recommend a heat only boiler and unvented cylinder but there are combis out there that can do the job alphas Flows smart for one , as others have said you would benefit from upgrading your incoming water supply first you can only get out what you can supply. Cheers kop

Screenshot_2017-10-27-06-07-19.png
 
try a viessmann 111 ideal and will run 2 showers no problem after your water mains upgrade
 
Personally I wouldn't install anything but an unvented cylinder and a System Boiler or Regular Boiler in your house.

However, If you are going to go down the Combi road, look at the 938 Vaillant.
 
As mentioned few times above @Last Plumber and @king of pipes , unvented cylinder with a system boiler best option in my opinion. If you would go for underfloor heating too that would be a great setup of a system. If you decide to have ufh and have got more than 3 zones then you'll require a low loss header too. So basically take the recommendations you got from the engineers above and you can't go wrong
 
If your planning on running more that one outlet at the same time at minimum I would suggest a storage combi e.g. Viessmann 222

But your better going with an unvented cylinder and heat only boiler

But as you've already said water main is key, I would be looking at minimum to feed two outlets 3 bar and 25-30lpm
Have you ever installed the viessmann 222 condensing storage boiler ?

Is that as powerful and efficient as a system boiler setup ? What minimum lpm and bar do you require to install that type of boiler? I am thinking to suggest it to my parents in law as they've got currently an older combination boiler of viessmann but had recently a lot of hassle with the hot water.

They've got 2 bathrooms too and about 10 rads
 
Have you ever installed the viessmann 222 condensing storage boiler ?

Is that as powerful and efficient as a system boiler setup ? What minimum lpm and bar do you require to install that type of boiler? I am thinking to suggest it to my parents in law as they've got currently an older combination boiler of viessmann but had recently a lot of hassle with the hot water.

They've got 2 bathrooms too and about 10 rads
No answer , is also an answer ... fair enough.
 
No answer , is also an answer . fair enough.

Your the person designing / changing the system for them so you should know there hot water requirements

How do I know how much hot water they need
 
Your the person designing / changing the system for them so you should know there hot water requirements

How do I know how much hot water they need

I asked totally different questions. I just wanted to know if you installed the viessmann 222f before? And how good is this type of boiler and storage compared to a system boiler with an unvented cylinder. I mean the hot water isn't great once the second tap is opened. The pressure drops significantly in the shower. I was thinking either the boiler is wrongly sized or it's just not the right system for this type of property. The shower struggles definitely when you open kitchen tap and shower in the same time it's really poor flow. They've got an older model vitodense 100 / 8 years old
 
I asked totally different questions. I just wanted to know if you installed the viessmann 222f before? And how good is this type of boiler and storage compared to a system boiler with an unvented cylinder. I mean the hot water isn't great once the second tap is opened. The pressure drops significantly in the shower. I was thinking either the boiler is wrongly sized or it's just not the right system for this type of property. The shower struggles definitely when you open kitchen tap and shower in the same time it's really poor flow. They've got an older model vitodense 100 / 8 years old

That screams either low cold flow and pressure or low hot lpm
 
That screams either low cold flow and pressure or low hot lpm
Could you I prove the low hot lpm ? They've got 3/4" steel water supply as far as I can remember. I'll check once I'm there .perhaps you can point out what's the best option for hpthe
 
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