Refilling ch system

[Mungobiscuit]

Dear All,
Can anyone explain why a new towel rail will only fill about half way up on a gravity fed, fully pumped, vented ch system. I thought that any item in the system that was lower down than the f&e tank would naturally fill due to gravity.... towel rail is on the top floor, f&e is in the attic, about 1.5 metres above the top of the rail..... Its got me confused as some of the rad's downstairs are also reluctant to fill.... In the end, I've only managed to fill the system by pouring water into the towel rail...

 

[CBW]

If it’s an issue filling, sounds like a blocked or partially blocked cold feed.

 

[Mungobiscuit]

Yeah, I thought that but checked it and it's clear. I figured it might be the mid position valve so I set it to manual but the water flatly refuses to fill to the required level on the towel rail.... Got my brain aching.... Lol.... Could an airlock cause it? I'm working on a shoddy system that has pipes running downhill etc etc.... 1980s build....

 

[oldbuffer]

Assuming the bleed point is at the top of the towel rail, on one side, can you gently loosen the blanking plug on the top of the radiator but on the other side? Don't take it all the way out, just unscrew perhaps 1/2 to 1 full turn. The way some towel rails are constructed does seem to lead to internal airlocks. The air escaping from the loose plug may be enough to get it working.

 

[Mungobiscuit]

Thanks buffer, tried that as I've been caught out by the Chinese import towel rails that have internal baffles, but it makes no difference..... You can actually remove the blanking plug completely, whilst the valves are open to the system... With no sudden rush if water...... Thing us, once I've primed the system by several refills from the towel rail, it runs and heats up just fine, so it's getting circulation and flow.... I reckon its 2nd in the radiator circuit of 7....1 to 4 being on the top floor..... Filling the system from this point does create quite a lot of noise at the circulation pump so I have to assume that this is air escaping from the pipes under the floor??