We have a small one bedroomed house heated by a combi-boiler and, at the moment, four radiators. Basically I want to add a couple of extra radiators in the small hallways (if thats the right term, they ARE small) at the front and rear of the house.
My plumbing experience so far consists of moving and replacing two radiators and I'm reasonably confident with pipework. I have tried reading up as much as possible and know a little about flow and return pipes and not connecting radiators in series. What I'm not sure about is how I connect up the two extra radiators as there is no access (without major work) to the flow and return pipes coming from/to the boiler. I do have access (from the cellar) to the 15mm pipes feeding the living room radiator though. Can I tap into these? As far as I can tell, the flow/return pipes from the boiler simply run vertically down the wall (boxed in and behind work surface)from the boiler in the bathroom and come to an end below floor level in the corner of the kitchen directly below with 15mm pipes coming off feeding each of the four radiators.
Hope I've made myself clear and not waffled too much - first post!
Any advice greatly appreciated.

Raif wrote:

the living room radiator though. Can I tap into these? As far as I can

The short answer is yes.

As long as the living room radiator is not huge (and hence using all the
capacity of the 15mm pipework) you should be fine. Even then it sounds
like you only need to add small extra rads so its unlikely to be a
problem either way.

--
Cheers,

John.

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Thanks.
Thought/hoped that might be the case. Not sure if the two current radiators on each floor are connected independently to the flow and return pipes from the boiler or whether one feed covers two radiators - if you see what I mean?!
When you say huge, how huge is huge? ie what is the capacity of the 15mm pipework?

I do have access (from the cellar) to the 15mm pipes feeding
the living room radiator though. Can I tap into these?

It is quite likely that you can just use those pipes. 15mm pipework is good
for 6kW, IIRC, which easily runs 1 large and 2 small radiators. My 3 bed
house was plumbed with each floor sharing one 15mm run, joined together by
22mm runs to the boiler, although I've modified it so that each 15mm run is
off its own zone valve, with a new 22mm to the loft where the boiler is.

Your main problem is if the main trunk of your system is run in 15mm, which
could be quite marginal to run a 1 bedroom house from. You may need to turn
the pump up in this case and it might get noisy in some circumstances. If
so, consider replacing the pump with a Grundfos Alpha model. This would be
cheaper than replacing the congested sections with 22mm, although, perhaps
not quite as effective.

Christian.