Additional rads

[Bullbags]

I need to add 2 new rads to a system in a three storey house. The house has a Ravenheat combi boiler in the kitchen and currently runs 5 rads. I need to add 1 rad to the top floor and one to the second floor.
My plan was to t off from the rising flo & return pipes in the top floor and run 15mm pipes to the required rad up there, about 8-10 metres. I was then going to t off from this and drop down to the next level to plumb in that rad (adding an extra 8-10 metres).
I noticed that the rads on the second floor were hot but the one on the third floor was luke warm.
Does anyone see any problems with my suggestion? I am concerned that I am adding pipework to a system that runs over three floors and I'm concerned whether the combi will cope! Didn't want to install the rads to find that the combi couldn't cope.
I am hoping that the luke warm rad on the third floor was just a matter of balancing the system.
Any thoughts/ideas/experiences welcome.
Cheers.

 

[Bahco]

You may need to up the system pressure a little to ensure the new rads will work.

Look in the FAQS for rad topics.

 

[superdupergasman]

your top floor rad as Bahco says will need some extra system pressure to allow you to blead it properly and get it working.

Pressurise system and blead, then it should operate correctly.

You plan sounds fine and this combi should be able to run the rads no problem although you should look into what the manf says about range rating the appliance for central heating (more rads = increase setting on boiler). see what yours has been set to. Perhaps a job for a RGI.

 

[bab]

ya combis gona be at least 24kw so the rads r no problem. Id add the extra & only check the boiler if its struggling as i find most small systems rarely range rated as lots of installers seem to do the bare minimum & leg it, probably still set as it came out the factory.

 

[Bullbags]

Cheers for the advice chaps

 

[Bullbags]

What does "range rated" mean?
Are there any basic guidelines in terms of boiler size (KW) and the number of rads it can run?