Change from heat only to combi boiler

[Andy B 23]

I am considering changing my heat only unvented system for a combi, the set up is follows:

3 Bed detached house constructed in 2011, 50mm slab insulation boards in the cavity (traditional masonry internal & external skin walls).

Potterton 12 SL Promax heat only boiler.

Family bathroom: bath with mains fed thermostatic shower.

En-suite: mains fed thermostatic shower.

Downstairs WC.

2 adults & one teenager in the family, only one bathroom used at a time.

Being a modern insulated property the radiators are on the small side, the exposed pipework to the rads is 10mm copper, 22mm copper can be seen in the airing cupboard for the flow & return etc. 12 Rads in total, 10 type 11's & 2 type 21's (single convector) 10 of the rads have Myson TRVs.

We are now fortunate enough to live in South Devon so the climate is milder, the boiler does not work as hard as our previous boilers did in Yorkshire.

2 Reasons for changing the system, firstly the age of the boiler (13 years old) & secondly the tank is located in the airing cupboard above the stairs, with the tank gone I can gain access to the loft without taking any space from the rest of the house.

Looking for guidance on the size of combi required as well as preferred makes/models.

Thanks in advance.

 

[muggles]

You need to know your incoming mains flow rate & pressure as combi boilers are partly specified based on that. As you have a bath, a higher power boiler would be more appropriate in order to give acceptable filling times. You'll likely need a gas pipe upgrade from the meter to the boiler.

 

[flameport]

firstly the age of the boiler (13 years old)

Is the boiler broken beyond repair?
If not, it doesn't need to be replaced.

the tank is located in the airing cupboard above the stairs, with the tank gone I can gain access to the loft without taking any space from the rest of the house.

Move the cylinder into the loft.