An interesting enigma!

[The Plumber Guy]

I have a customer who had an extension built 3 years ago and part of this was the inclusion of a very large radiator, to heat his lobby, which has never worked properly. The thing is about 2.5m long with double panels and double convectors whereas all the others in the house are single panels. There are no airlocks in this rad' and when the one in the loo immediately before it is switched off it gets hot but still doesn't work the way it should.

I'm thinking a) that when the small rad is on it takes the heat away from the big one and b) that the big one needs to be changed for a smaller one that will work.

Anyone got any other thoughts? All the best to you

 

[dontknowitall]

Is it a one way TRV? Are the pipe sizes logical (e.g. 15mm to the loo rad and 10mm to this rad is not logical!) Is it on a one pipe system? Is the pump powerful enough to shove the water to this radiator? Presumably the TRV is working well enough? Also presumably air is allowed to move around the radiator? I'm not expecting answers but sorry about all the questions but these are some of the things I've picked up when trying to identify problems like this.

Also the radiator seems very large. If you measure the room width x length x height in metres then take this number times 45 divided by 1000 you'll get the wattage required and then you'll know (look in a Screwfix catalogue) what size radiator you can get away with.

 

[wheeto]

Is the loo rad properly balanced with lockshield? Possibly an old single-pipe system badly extended (two radiators in parallel over the same section of single pipe)? And I like the directional TRV thought from DKI

 

[The Plumber Guy]

Thanks for these answers - they're certainly giving me a bit of direction. Speaking of which, as I'm fairly new to central heating, what's the problem with a one-way TRV?

The problematic radiator doesn't have any TRVs as it's in the same room as the wall thermostat but the loo rad does. The rad looks way too big for the size of room; am I right in thinking that a single pipe system is the same pipe feeding and returning from one radiator to another and getting cooler as the rads go away from the boiler?

Again thank you for your help. This is a great forum and with a bit of experience I hope to be able to contribute in future.

 

[wheeto]

Originally TRVs could only cope with water flowing one way and incorrect installation, leading to anything from severe water hammer to complete failure open or closed, was common. Then there were reversible types which had a selector. Nowadays I think most are completely bi-directional so the problem has mostly gone away, but if you encounter an older installation it's something to check for.

 

[wheeto]

For one / two pipe systems, see diagrams here:
Two Pipe System

Incidentally, what we in Britain call a one-pipe system isn't really ... that honour should go to the american single pipe steam system which just had one pipe attached to each radiator. Steam rose into the radiators, condensed and then the condenstate ran back through the same pipe to the boiler to be re-heated.

 

[justlead1]

Hi. If you fit a smaller rad it will not give more heat than the large one you have. As its the amount of heat/water the pipes are carrying that that seems to be the problem. Try balancing the whole system using the lock shield valves, this may push a bit more where you need it.

 

[dontknowitall]

Although more costly, I felt that a smaller rad would be a better solution than trying to re-balance everything - but I'm more than happy to give way with that idea.

Gut feeling with this is there is something in the pipe layout that's not quite right.