cold radiator on indirect two-pipe system

[FrankieF]

Hi,
Hope you guys and gals can help.
I have a two-pipe indirect system, fired by an oil-fired boiler, the pipes are inverted and run in the loft of a single storey(bungalow) house. One of the rads remains cold, even after the boiler has been running for some time. Each area has drain-cock valve as inverted, and cannot get any heat to go into the rad unless drawing water off using the drain cock for that rad.....and once turned off, the rad cools down again. Have drained the system several times, also added cleaner and flushed after a week...but with no luck.
There are also two pressure release valves in the loft(not sure whether they should be there, as indirect system?? one has a leak which I am fixing tomorrow, would this affect the rad?? would an air lock cause this?? only that have drained system and refilled, so air lock should dissappear anyway.
Sorry for the long thread, but had lot to put in...

Any help would be very much appreciated. Thanks in advance.

Frankief

 

[waterbuoy]

is there a trv on the rad

 

[FrankieF]

no trv's on any of the system, valves fully open....thanks for replying

 

[waterbuoy]

have u tried running the system with all the rads and the cyl shut exept the rad that wont get hot

 

[FrankieF]

I havent tried yet, but I understand that it has been done before, and it worked only temporarily, if that is any help

 

[waterbuoy]

no not really if its air when u try running only the dodgy rad u should hear the air pass through that part of the system also the pressure relief valves in the loft you refer to are probably either auto or manual air vents can u describe what they look like

 

[FrankieF]

They are manual air vents, as can only get air to escape when twist nozzle at top, one of them has a leak where the 22x22x15 reduciing tee is fitted, can this prevent the system from pulling the water thru the return pipe?

 

[waterbuoy]

in a word no but that hasnt cured the problem lets go through this again its a bungalow the primary flow and returns run around the loftspace and there are drops to all the rads

 

[FrankieF]

Yes, there are a lot of loft boards down, which means most of the pipework is not exposed, except for the expansion tank, and the pipe work to and from boiler, but can't get to where any of the drops are, without removing boards. What was confusing me is that when I drew water from the drain-cock below the didgy rad, the Primary flow and rad heated up ok.....?

 

[waterbuoy]

are the drops from the loft to the didgy rad all exposed

 

[FrankieF]

unfortunately not, it cant be just a simple airlock can it? there is no sign of a leak, except for where the prv is......what can the cause be, would the pump be the problem, as it is the furthest rad from the pump and boiler, drawing the water thru was only pulling it to heat up maybe, not looked at the pump setting?

 

[evsy01]

take a look at the pump. it could be set too low. if its modernish there will be speed settings try and turn it up but keep an eye on the f+e tank for expansion pipe overflowing

 

[waterbuoy]

frank tried anything i suggested last night

 

[FrankieF]

fixed the leak near the prv, and still same problem. Pump is set to its highest speed, so no luck there. If I get to remove the boards in the loft, what could it be that i am looking for? I havent tried the test where only have the dodgy rad on, but owner says that tried that before, and did work for a while then stopped after a few days......
Really appreciate it that you guys a responding back.....

 

[WHPES]

Are there any sections of pipe which might be airlocked?

 

[FrankieF]

possibly, but as i've mentioned before, I have drained down that section of pipework, as its an inverted system, any airlocks would have cleared wouldn't they??? also drawing the water to the drain cock was making the rad warm up. so the only question, is if there is a problem past the drain cock on the return pipe back to the boiler maybe??
This is definitely a strange occurence....