New Boiler Advice - 30i or 38CDi

[tkaravind]

Hello All,

I am getting some quotes for a new boiler to replace a very old one.
But confused between the two options available:
Worcester Greenstar 38CDi Classic VS Worcester Greenstar 30I ErP.

Mine is a 4 Bed 2 Bath Semi with 12 radiators.
We use hot water (showers) from both the bathrooms simultaneously at times.

I have two specific questions:
a) Would I be better off with spending a little more on 38CDi (that according to Bosch specs is meant for highest hot water flow rates)?

b) The incoming water flow rate was measured at around 11-12 l/min (by a heating engineer giving me the quote) ...based on which I was advised to stick with 30i as I won't see the real benefit of 38 CDi at that flow rate.
Is this correct?
While this sounds reasonable, will the incoming water flow rate be a significant factor in choosing the right boiler size?

(Some of my friends whose water supply is similar to mine, have still gone with 38CDi and report great hot water hitting their showers.
Not sure if they would have seen the same with 30i though.)

If other hot water sources ( like taps in kitchen etc) are used at the same time as the showers, will 30i struggle to keep up?

Any advice on this very much appreciated.

Thanks all,
Aravind T

 

[ShaunCorbs]

Wrong type of boiler if you want to run more than one outlet at the same time

Bigger issue is your water main if the figures are correct isn’t suitable to run more than one outlet at the same time

Need to know if them figures are correct you can test your self by timing how long it takes to fill a 1l bottle around 4 seconds for 16lpm

As for pressure you would need a pressure gauge or you can pay a plumber to carry out these tests and report back

 

[Scott_D]

As above
12lpm isn’t enough to supply to outlets at the same time

 

[gmartine]

Yes to b), go to your friend's houses and actually turn on both hot water outlets/showers and actually see and feel it for yourself.
After spending thousands on a new boiler install nobody admits to making a mistake.

 

[centralheatking]

Its just not good practice to use a combi in your intended manner.
Usually unqualfied engineers for pressure cylinders go down this route. You will not get proper performance. Times of water stress Summer, every weekday morning it will just be a bind. The pages of UKPF are awash with the 'big Combi Problem' centralheatking

 

[tkaravind]

Thanks all for the advice. I now get the idea about the outlets I can use.
However even if I stick to one outlet at one point, with the incoming mains
at 12 l/min..the 38CDi Worcester boiler won't be of much use?

i.e on the Bosch website its spec ed to deliver upto 16.4 l./min.
But if incoming is only 12 , that is effectively the upper limit any boiler can output?

 

[ShaunCorbs]

If that’s correct better off going with the 30kw as you say your not going to get the benefit of a bigger one as your main is capable

 

[Harvest Fields]

Is your main 15mm pipework?

 

[tkaravind]

Yes they are 15 mm pipes

 

[centralheatking]

As above tkar if you want good or even optimum performance
for 12 rads 4 beds and 2x bathrooms with plenty of people in your
gaff...as you state 2x showers at same time you are totally in the wrong ball park by even considering a combi, and bin any installer
whom advises you down this route. UNLESS. you cannot afford a proper set up....centralheatking