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View the thread, titled "New Rads in extension not heating up" which is posted in UK Plumbers Forums on UK Plumbers Forums.

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D-Ireland

Hi all, new to the forum so any help very much appreciated. Let me apologise for the length of the post!!

We live in a bungalow with 10 existing radiators, some single, some double.. Existing boiler is a 50/70 oil boiler. We recently had a new extension built with 3 double radiators installed. The plumber initially ran a 15mm feed and 15mm return pipe off the existing 15mm pipes which were supplying the exiting kitchen radiator. While the existing rads were still heating up as well as ever, the rads in the extension were getting only lukewarm. Its quite a big space, about 480sq feet in total with vaulted ceilings, so if the rads aren’t at full heat it’s not going to heat up.

The plumber then brought a 22mm pip from the main 22mm pipe into the extension and then ran the 3 new rads off this using the 15mm pipes he had already laid (and were now screeded over). This improved things but not significantly.. He then installed a different (used) pump and reversed the flow to rule out a pump fault. Again there was some improvement but the new rads are still nowhere near as hot as the radiators in the rest of the house. Another issue was that the thermostatic valves (these are only installed on the new rads and not the old ones) seemed to be kicking in and shutting down the rads which would suggest the heat was getting to the feed pipes ok. We have removed the valves in the short term. The plumber has balanced the rads.

The builder and plumber are thinking the boiler may not be big enough/working well, but I would have thought this would result in a drop in heat for all rads and not just the new ones which makes me think it’s a circulation/piping issue? The existing rads are piping hot. Has anyone got any advice? In fairness to the plumber he has been working hard to get it sorted. If you need further info please let me know! Many thanks.
 
Sounds like a balancing issue and the fact that your trying to heat a massive volume with 15mm pipe . But like trying to fill your petrol tank with a drinking straw?

You haven't got a plumber you've got a nugget with a spanner? Boiler be fine it's the pipework.
 
I wouldn't have 3x 1mtr doubles off 15mm pipe, you may be able to get it right through balancing the whole system and forcing it through.

Thanks Millsy. I assume the issue here is that the water will just bypass this loop due to the pressure differential trying to force the water from the 22mm pipe into the 15mm pipe? I have seen on here that plumbers have whole systems done on 15mm with no issues.
 
It all depends on the size of radiators, pipe runs etc. you can't just throw some rads on a wall. And hope they will work
 
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