Which boiler?

[Hobo128]

Went to a job the other day, quite a big house. 12 rads and three bathrooms.
They have a conventional boiler in at the mo but want to upgrade. As there is only two people living in this house with no kids I have told them to go down the combi route. They agreed but later on told me they would be worried about if people come to stay then the combi may not match the demand of hot water if all bathrooms were being used. Obviously a system and unvented cylinder would be best route but as the are two people living there most of the time I see that heating the water in the cylinder could be a waste of energy.
I have now started looking down the worcester highflow 440cdi and 550 or the vaillant 937 boilers.
Has anyone fitted these and does anyone know what they are like and would they be sufficient.

Cheers

 

[Ray Stafford]

I would go back to the system boiler and UV route provided the incoming main would support it.

Standing losses on a modern 250 litre unvented is just over 2kwh/day.

Thats about 6p per day, I think - or £22 per year "wasted". Compared with the wasted water run out whilst waiting for a combi to come up to temp.

Or am I missing something?

 

[Riley]

I think just for uninterrupted service as long as the mains can cope then unvented all day long mate

 

[jtsplumbing]

As others, 3 bathrooms along with other hot water demands not a good idea to fit a combi .

 

[Hobo128]

Ok so I have decided to go for the worcester 24 I green star system with the integral diverter valve. Going to keep the old copper cylinder and create a sealed system. Seems to me the bestate option for every eventuality.
Has anyone use this system before and how are they?

 

[LPC]

Personally mate I'd think 24kw would be underpowered unless the 12 rads are very small. I 'budget' 15kw for an unvented if i'm doing ***-packet sizing so I would go with something ~30kw for an unvented with 12 rads. They must be fairly large in a property with 3 bathrooms.