Is switching to a combi boiler in a large-ish house really such a bad idea?

[Northman]

So far no one has actually explained what the reason for no combi boiler is - It seems to me gospel that a large house needs a system boiler just in case two people use the bath at the same time and the kitchen sink is switched on - Even under those circumstances a bit of low pressure is not dramatic

And dont get me started on the excuse that at Christmas your boiler might pack up - Thats not an item that factors into it

I have a system boiler Ideal Mexico 2 beast on a one pipe system and even I considered replacing it with a combi

I once rented a house where the rather ancient Potterton cast iron boiler gave up on Christmas Eve. Not a lot of fun with 4 young children and snow on the ground.

When we bought our current place (large detatched house with two bathrooms) the same model Potterton boiler was in place (open gravity system with pumped shower) and we decided to replace it when it must have been at least 45yrs old and still working well. Had a chat with a couple of different companies about its replacement, and eventually went with a system boiler and unvented tank. Although there are just two of us at the moment I had in mind both the likelihood of family visits (children with spouses and/or grandkids) and hence the need for a robust hot water delivery, and the potential future resale attractiveness of that for prospective buyers with a young family.

In practice the main reason I'm so pleased we went with the unvented is the wonderful shower it produces (we have excellent water pressure/flow to the property). Every morning I have a shower that I would say is as good as it can be - better than I've experienced in many upscale hotels.

In terms of back-up, whilst I agree that a boiler breakdown over Christmas is not that likely (but does happen!) we have in the last couple of years had a number of power cuts - at least 3 last year of which one was over 24hrs. The unvented tank meant that we did at least have running hot water, and could shower (even if it was by torchlight). Every situation will be different, but I think as a general rule-of-thumb the larger the house/household the more likely that a system/unvented design is the way to go.

 

[JohnD]

You seem concerned at the room a boiler will take up. I don't understand that. I have a Viessmann that fits in a 400mm tall wall cabinet (in fact it is not a cabinet, just a gap with a door, open top and bottom.

 

[fixitflav]

Every situation will be different, but I think as a general rule-of-thumb the larger the house/household the more likely that a system/unvented design is the way to go.

That's an argument against combi, but it doesn't have to be system boiler. Unvented on the HW secondary side for a good shower, but the primary can be a system boiler, or a heat-only unvented with expansion vessel, or heat-only open vented with F/E tank. Advantage for ease of maintenance in having pump etc separate from the boiler.