New radiators don't warm properly

Postby tofteo » Sun Oct 28, 2007 12:22 pm

I have fitted newer modern radiators to replace the cast iron radiators in two of our bedrooms. However, these are not warming properly at all, even though I have bled the air out completely - they initially fill with hot water then, but the heat disappears so I can only assume the water is not flowing through properly.

These have isolation valves and TRVs fitted, so I wonder if the smaller bore of these compared to the larger bore of the old radiators and fitting is constricting the flow? I have removed the top sections of the TRVs on both the flow and lockshield ends, i.e. they are fully open and the pin moves freely to open position, but this does not make any difference.

I have also tried closing all the other radiators in the flat to "force" the hot water through the new radiators, to no effect - perhaps because we are on a communal system feeding all the flats in our block this kind of balancing would not work anyway, ie. as the other radiators in other flats on the circuit would be fully open?

I also tried disconnecting the pipe from the valve on both the flow and return sides to make sure water flows freely and there are no blockages. When I disconnect from either end, the water flow through the radiator and out the other end into my bucket freely - and its hot. Its just when I have both ends connected, the radiator slowly loses heat (again, even after I have checked for air and bled it).

Running out of ideas (am replacing the TRVs with standard valves next to see if that helps), so advice would be appreciated.

Rgds, OT.
Rank: Labourer
Progress to next rank:
Posts: 1
Joined: Sun Oct 28, 2007 11:53 am


Simply Build It

Postby Bay Plumbing » Tue Oct 30, 2007 8:37 pm

Hi tofteo,
To start with if your system is a one pipe system(rad heated by one pipe so that the water flows through rad and out the other end) if this is the case then you need to put the flow in the top and the return in the bottom this may help and you may have me stumped-htg engineer is usualy good at these things but give this ago first.

hope this helps let me know how you get on,

Bay Plumbing
Rank: Tradesman
Progress to next rank:
Posts: 40
Joined: Sun Oct 21, 2007 10:31 am

Display posts from previous
Sort by
Order by

  • DIY How to Project Guides

  • DIY how to tutorial projects and guides - Did you know we have a DIY Projects section? Well, if no, then we certainly do! Within this area of our site have literally hundreds of how-to guides and tutorials that cover a huge range of home improvement tasks. Each page also comes with pictures and a video to make completing those jobs even easier!


  • Related Topics