Upstairs radiators work, downstairs ones don't

17 Dec 2008
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United Kingdom
Hi All

I replaced my central heating with a Vaillant ecoTEC combi boiler that is feeding 4 radiators downstairs and 5 upstairs (3 norm. size bedrooms + 1 bath + 1 toilet). The problem is that the downstairs radiators don't work properly; two of them get only lukewarm while the other two are just cold. All the upstairs ones work perfectly well. I have done the bleeding of all the radiators and apparently there is no air in the system. The pressure on the boiler's pressure gauge is also fine + there are absolutely no problems with the hot water upstairs in the bath and downstairs in the kitchen.

The boiler is fitted in the kitchen downstairs and I believe the problem is the way the plumber (whom I can't seem to find now) has connected the FLOW pipe; the FLOW pipe comes out of the combi and then there is a T-junction that distributes the heated FLOW water for upstairs and downstairs radiators. However, the piping from the T-junction to the first downstairs radiator is at least 5 times longer as compared to the first radiator upstairs. I have tried turning off all upstairs radiators; this makes the 2 downstairs rads work fine (almost) but the rest of the 2 get just barely warm. However, the moment I slowly turn on the upstairs ones, the downstairs rads gradually get back to the previous behavior.

Any advice from you guys will be greatly appreciated.

Many thanks.

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or as so many people dont do, the plumber failed to balance the system. you'll find all your lock shields are fully open in the rads.

read the faq's on balancing and everything will be just fine. :)
Many thanks for the reply.

Excuse me for my ignorance, but is it OK to connect the FLOW from the combi by a T-junction to feed the upstairs and downstairs rads, especially when the distances to the radiators are so uneven? I have seen in some houses that the FLOW has a top-down architecture where it first goes up to feed the upstairs radiators and then the pipes come down for the downstairs ones.
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Great! I will try out the balancing soon.

However, I have noticed that all radiators have got wheelhead valves on both sides (no lockshields or TRVs). Could you please confirm if the lockshield valves are fitted on the return side? If it's true, then I should do the balancing with the FLOW wheelhead valves fully open and controlling the RETURN wheelhead valves uptill the 11 degrees C differential temperature.

tbh it doesnt really make a difference. what i would suggest though is that you choose just one end on all the rads to be the 'restriced' end, put a mark on it with a perm marker and instruce everyone in the house that if they want to turn a rad off, only to use the unmarked end.
Sorry for being such a nuisance, just one last question; let's say that with the 'unrestricted' end on the radiator fully opened, the 'restricted' end is fixed to a setting such that the temp. difference is 11 degrees C. Now, if I change the 'unrestricted' valve to a new setting (e.g., close it down a little bit), shouldn't that disturb the balancing as the differential temp. was balanced with the 'unrestricted' valve fully opened?
to be truthfull ive never checked the differencial temp on the boiler. the balancing is more to create a resistanc ein the system and force the water down the harder to reach rads. hot water always wants to rise in a system, hence all valves fully open creates hot upstairs cold downstairs. i nearly allways find that knocking the upstairs to 1/2 to 1 full turn open and downstairs fully open sorts things nicely.

you can of course set it much more accurately but my way seems to do the trick.

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