Combi boiler advice vaillant 938 actostor

[Angel141077]

Hi we currently have a 16+yrs old boiler (potterton prima) and we are having a 2 storey extension built on our 4 bed detached house. We currently have 1 bathroom, 1 ensuite, 1 cloakroom. There is only 2 of us in the house but I wanted some advice on whether you think a combi boiler would be suitable for us. It does state this combi (vaillant 938) is suited to larger houses. We currently have around 12 radiators and probably adding another 6-8 once the extension is built. Any advice would be appreciated thanks

The ability to heat radiators is unlikely to be a problem, but hot water might be.

how many bathrooms and shower rooms will the house have when it is finished? And how many bedrooms? Do you like hot baths?

A combi needs good incoming flow of water. Fill a bucket at your kitchen sink cold tap, time it, calculate how many litres per minute it delivers. Check also at the garden tap and utility room tap if you have them.

Your installer should do a more detailed measurement before recommending a boiler system.

How old is the house?

The house is about 20 yrs old. There is no increase to the amount of bathrooms just increasing the main bathroom size to fit a bath and shower relocating an ensuite (wet room) and no increase to bedrooms just a larger bedroom and larger living room. Love a hot bath occasionally but we both live by our showers. Apparently we have a good water pressure one plumber did test that to see if we would need an accumulator. One plumber suggested a pressurised system with a larger tank in our loft , thought that was potentially overkill just for the 2 of us. The other suggested the vaillant combi boiler ?

so you'll have a shower and a bath.

The boiler you mention has a small hot-water store, but it can't push the water out faster than the watermain supplies it, so still worth doing the bucket test. There are people who buy a 20 lpm boiler but only have a 10 lpm supply. Bit of a waste.

Try the bath hot tap as well, to see if it will fill more slowly once you change.

A 20-year old house probably has an incoming supply in blue (or black) plastic. Can you see its diameter?

I will check thank you for your help !

Hi piglet John
It took 30 seconds to fill a 12litre bucket from the kitchen cold tap.
It took 50 seconds to fill a 12 litre bucket from the bath hot tap.

sounds like you will be OK with a combi then.

Thank you for taking the time to respond and offer your advice ... appreciated

PigletJohn you are The Great Wise Man of Boilers!

Very interesting.

behold

Really? So if the storage tank is filled, it won't pump out that water at 20lpm, then when empty switch to the mains water pressure?
We've only got 11lpm but there's only two of us in the house, so I was hoping we'd get that pressure until the tank was depleted.