combi or system boiler?

22 Sep 2009
Reaction score
United Kingdom
Hi, We are having a loft conversion and we're a bit confused over which option to go for combi or system boiler?

our cold water pressure is 22L/min.

I have been advised to have installed a worcester-bosch 42 cdi this gives an output of 17l/min

will this be sufficient for a shower in the loft extension?

will this cope with a bath being ran in the bathroom on the 1st floor and the shower working in the loft extention?

system boiler we are being advised on is a heatrea sadia?

many thanks .
Sponsored Links
Any combi will only run one hot water outlet properly!

It also needs to be installed properly.

You dont have a pressure of 22 li/min as pressure is measured in Bar.

Its probably an open pipe flow rate. Thats an indication but whats needed is the dynamic flow rate at a residual pressure of say 0.5 Bar or 1 Bar.

Dont expect the flow rate through the boiler to be anything like that but without further measurements its difficult to predict.

Anyone quoting for a combi boiler or an unvented cylinder should have measured the static pressure, the flow and the dynamic flow rate to know how each is likely to operate.

There are many fitting things who have limited understanding of how they work.


DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links