Weird towel rail behavior!

[LeonR]

Hi again, i'll try and keep this as short as possible with all the facts, hopefully somebody can help me understand what is going on (I suspect it's an air lock somewhere).

1970's CH, gas boiler, gravity fed, no diverter valve, header/expansion tank present, CH pump has direction arrow pointing downwards.
Rads on 8mm and 10mm, out and in manifolds on both floors.

I removed two radiators (old) in one room and replaced it with one new radiator on the same piping (each rad has it's own run from the manifolds).

New radiator works, it's balanced , all rads come on and get warm at about the same time - all good here.

The problem (probably due to draining rather than the new rad)

Two towel rails (different rooms, same floor, 15mm), I assume connected to the 'hot water loop' (whatever the term is), after draining the CH (I opened the towel rail/rad valves to fully drain) and then refilled the system, one of the towel rails doesn't seem to heat up properly anymore.

Strange symptoms

When CH is off (hot water on obviously)
Towel rail cold, not much flow from the vent valve at all, the LEFT pipe is warm/hot , RIGHT leg is cold.


When CH is on (all upstairs rad's closed as a test)
Towel rail heats up fine, however the LEFT leg is cold, the RIGHT leg is hot (they switched around??)


When CH is on (and rad's open as normal), towel rail is slightly warm, but not hot.


Note: the other towel rail is 100% fine and when I open the bleed valve the water pressure is minimal, the water is constant, but it's just drizzling out.




Sorry if that was a bit long winded, i'm just confused about how it can work 'sometimes', it's almost as if it can't get warm enough to start the flow?
Each pipe as a valve on it, so I am free to play around with those.


All rads and hot water is fine.


Any help appreciated!


Thanks,
Leon

 

[Masood]

Did you modify any pipework when you installed the towel rails? The switching around of which pipe gets hot when heating is on or off sounds like reverse circulation taking place.

 

[LeonR]

Nope, this is basically what I did:

Drain CH (one drain valve), open all upstairs bleed valves including towel rails.

Track down the feed and return which goes to bedroom 1 , this had a T compression on each to connect two radiators , I got rid of the T (removing one radiator) and used soldered connectors instead, I then switched the radiator which was remaining with a new one.

So basically tracked the two pipes going in to bedroom 1 and routed them directly to a new radiator.

The TRV is bi-directional so I can't really go wrong here (I don't think)


Update: the towel rail seems warm again now, the heating has been on for about 6 hours and I wonder if this has done something to assist? (heating now off and the towel rail still seems about the correct temperature).

Thanks,
Leon

 

[tamz]

There is a bit of an air lock in the pipes. Disconnect one at a time and draw water through or do it from the air vent.
The reason it swaps sides when on for hw and heating is its connected wrong and getting a bit of a back feed. Not much of a problem for a towel rail and more bother than its worth to fix.

 

[LeonR]

Cool thanks for the explanation , it seems ok again now so I'll leave it alone [emoji846]