UKC

Hey folks, may I 'plumb' the depths of UKC for a view on a heating issue.

One of my radiators is only getting partially warm when the rest are working fine.  The basic trouble shooting I have done is to bleed the radiator, make sure that the pin on the thermostatic value isnt stuck and to open the flow valve completely. This hasnt worked.

It gets slightly warm at the upper part of the radiator and cold at the bottom.  This is the first year that this has happened.  The system and radiators are only 9 years old, in full working order otherwise and serviced annually.

Any thoughts before I go splash £100 for someone to come out and do a quick fix.  Google has given some hints as mentioned above but after that it gets into the realms of technical which I'm not qualified to deal with, albeit I am pretty handy with good instructions.

Has it got isolating valves so you can take it out?

Even if it hasn't this is still an option, just be very careful of the carpets.

take it out see if it's full of crap, flush it with a hosepipe and see what comes out.

Close the valves at both ends. Loosen the fittings holding the valves into the rad, open the bleed screw and drain the rad. Lift it off the bracket and rotate it outwards so that the top is lying on the floor then undo the fittings, remove it and carry it outdoors upside-down so it doesn't dump black carp all over the floor. Flush with a hosepipe, replace, connect, refill. 

When I worked for a plumber a while back he taught me to wrap a rubble sack around the fitting you are removing to catch any leakage. Worked a treat at stopped may a carpet getting black stuff all over it.

It sounds like there is a very low flow of water through this radiator, could be the radiator or clogging in the pipework leading to it. You could as a test put a piece of copper pipe between the inlet & outlet valves in place of the radiator and see if it gets hot.

You reckon there are fish stuck in there? Worth checking, something similar once happened to Thomas the Tank Engine

Using the pipe and fittings like a hinge you say? They're not designed for that you know, and rads are a bit heavy even when empty. Sounds like a very good way to damage the pipes/fittings, and then you end up with water everywhere and no way to stop it. I bet this is what "I know best" bodger plumbers do too.

There could be a partial air lock in the pipes for that radiator, restricting the flow. Try shutting off all the other radiators and let the central heating pump push the air lock into the radiator (a few minutes should be enough).

Yes, correct; you can only do this if the radiator is quite small because they weigh a ton. Don't forget to close the bleed screw before heading off across the room or the rad will widdle black stuff everywhere.

But yes, the first test has to be to close all the other valves and see if the pump can push hot water through. If that works, gradually open the other valves to admit water to those rads thus balancing the flow. You don't need to valve to be open very far for water to flow. If you've got TRVs at one end, close the rad with the lockshields at the other end. While there's water around have a look and see if it's soapy - this is the Fernox, which is basically an alkali that reduces oxidation inside the steel rads. If it's not, add some Fernox to the header tank before you refill the rad.

Cold at the bottom and hot at the top could mean you have black sludge in it.   

Removing the radiator and cleaning it out might work if it's just that one.  

If not you may need a power flush.  

If you do go for the DIY empty and rinse, I'd suggest putting some anti corrosion stuff in when you refill.  

Are the pipes to the radiator hot? 

Sorry this is to TDB obviously 

I know from experience not to 'hinge' the radiator:  it caused a VERY fine pin hole leak which I spotted 5 hours before going on holiday!  The emergency plumber was very expensive.

That's why you should never undertake DIY on a house or car on a Saturday morning just before the proper plumbers, parts shops or other suppliers close. The same would apply to just before going on holiday! 

Should have got some JB weld on it if it was just a pinhole leak. 

https://www.jbweld.com/product/steelstik-epoxy-putty-stick

The pressure in a central heating system is pretty small and I've seen JB weld used to fix cracks in engines so it's more than up for the job.

Big thanks for this: have a few tediously minuscule leaks caused by flux left of copper pipes when the house was built 25 years ago - this me provide a decent botch job before expensive full repair.

Was it flux or was it little specks of impurity in the cheap copper pipes that were in use 20-30 years ago? We've had two pinhole leaks where there was no flux visible.