Choosing a new system, advice on my choices?

[SupraJames]

Hello!

My old gledhill gulfstream 2000 is on its last legs, and I think it's time to replace it. On the whole I've been happy with the system because it is all self contained in one cupboard and I had mains pressure DHW on demand and all was good with the world. The heating output of the gledhill is 29kw.

Since it seems these sorts of thermal store units are out of fashion, my choices are between a larger combi or system boiler.

It's a 4 bedroom, 3 storey house with 2 occupants and about 15 rads. We are very used to high pressure hot water so I think the combi route, while cheaper and maybe more efficient is a risk.

I am leaning towards a Vaillant system due to the good reputation and would be looking at an Ecotec Plus System either 630 or 637 paired with a unistor cylinder of some capacity.

I have a few questions for you guys!

- have I been too quick to discount a combi?

- would the 30kw output of the Vaillant 630 be sufficient assuming the 29kw of the gledhill was absolutely fine? Not sure if having a separate boiler and cylinder incurs losses! Any advantage going for the 637?

- how do I choose the capacity of the unvented cylinder?

- would I need an extra expansion vessel? According to the manual I have read the internal 10l one is good for up to 100l total system volume. Does the unistor cylinder become part of that system volume? I know in my current system the 70l thermal store is very much a part of the radiator system and shares the same water. Is this the case in a traditional sealed system?

- my radiator piping is microbore, 10mm I think. Would this be ok?

I do plan on getting this all done professionally but I would like to know enough beforehand to specify the important parts of the design!

Cheers

 

[nira49]

Hi SJ, what boiler did you go for finally? We are making a similar decision between system and combi for a 4 bed, 2 bath house with an active kitchen, so any insight appreciated

 

[SupraJames]

Hi SJ, what boiler did you go for finally? We are making a similar decision between system and combi for a 4 bed, 2 bath house with an active kitchen, so any insight appreciated

About 5 months ago I got a combi installed as this was the opinion of 3 out of the 4 installers I had quotes from. It's actually fine, rads get nice and hot and hot water is stinking hot so my misses can have her nuclear baths!

The boiler I went for in the end was a Vaillant ecotec 837. It's so much smaller and quieter than the old one, and a lot less complex than a system would be.

As my boiler is on the top floor of a 3 storey house I do get the standard delay for hot water down in the kitchen but once it's flowing its fine.

 

[nira49]

Thanks SJ. We too almost discounted a combi because suppliers told us that it cannot run two taps/ water on different levels simultaneously, but local installers are now suggesting we avoid an unvented system because of high running costs and additional building control requirements. I think we will go with the installers too. Thanks again

 

[Whitespirit66]

, but local installers are now suggesting we avoid an unvented system because of high running costs and additional building control requirements.

Did they have the G3 unvented ticket to be able to install these systems? If not, and that's what it sounds like, they may have tried to put you off of unvented so they wouldn't lose a job from you.

With 2 bathrooms and an 'active' kitchen, you are a prime candidate for stored hot water. Before going the combi route, get a couple of quotes and opinions from someone who is qualified to install unvented cylinders.

 

[Dean744PiN5]

+1 for unvented, a combi is unlikely to match your current hot water performance from a thermal store.