Radiator hot for a week..then cold.

[Cowboy10]

I've recently had my central heating balanced,as the front room radiator (last in the chain),was hot at the top,& cold at the bottom.

This was great,& the rad was working correctly.
However, within a week or two,it's reverted back to the above state,& this morning i've noticed it's stone cold.

My boiler is a Valiant Turbo Max.
I've tried for bleeding in the system. (There's no air found).
I topped up the system to 1.0 on the pressure bar (1.5 when it's on),as was recommended to me.

No sludge in the radiator,as i hosed it through about a month ago when i decorated that room.

As it's been balanced just a month ago,it heated up fine then,& it's slowly deteriated to it's previous state since,so i'm guessing it's not the balancing either!

i had another problem last week with pressure dropping,which i've now found to be a leaky TRV valve in an upstairs rad. That's now fixed,but it's not made any difference to the front room radiator.

I Even went to the point of turning off all the other radiators EXCEPT the front room radiator,but it was still luke warm/cold.

The radiator before in the chain (bottom of the stairs) works fine,so i'm assuming it's a problem with this paticular radiator.

I Can't shake the feeling that the fact it's the last one in the chain may have something to do with it.

If it'd been an upstairs rad i could have lived with it,but this is a main one in the front room & needs sorting.

Any ideas???

 

[kevplumb]

does it have a trv ?

 

[twgas]

Sounds as though you may have a blockage in the pipe to/from rad.

 

[Cowboy10]

Forgot to mention,none of the radiators are the thermostatic kind,just the on/off kind. i didn't know what they are called though!

 

[jackthom]

As twgas says it's probably a partial blockage in the pipes to the radiator.
Are they 15mm or something much less?

You might want to get your hands dirty and try the bucket test (remembering to top up the system pressure each time and ignoring the bit about the pump, assuming that's OK at the moment)

//www.diynot.com/forums/viewtopic.php?t=37170&start=20

 

[Cowboy10]

As twgas says it's probably a partial blockage in the pipes to the radiator.
Are they 15mm or something much less?

You might want to get your hands dirty and try the bucket test (remembering to top up the system pressure each time and ignoring the bit about the pump, assuming that's OK at the moment)

//www.diynot.com/forums/viewtopic.php?t=37170&start=20

I have no idea on the size of the pipes-they've been fitted behind the skirting boards. ( i would have boxed them in myself).

Thanks for the bucket test tip,that's something to try out,although
it appears when the system is emptied,it's fine for a week or two,then
deteriorates.

The system was emptied a few months ago when i decorated,& it worked OK for a week or two then hot at top/cold at bottom within a few weeks.

Then,a month ago i had another rad fitted upstairs, & had the system correctly balanced.Again, it worked fine then too.Gradually since then it's had the same symptoms as above,except today it's stone cold.

But thanks for the tipS, & i shall try that out,to rule out anything else!!

 

[jackthom]

That sort of erratic behaviour which is fixed by occasional draining and refilling might be a problem with airlocks in the system.

Is there any inhibitor in the CH water to prevent buildup of gases?

 

[Cowboy10]

My Dad gave me a hand looking at the troublesome rad a few days ago,& he noticed that the pipe that runs back to the boiler was warm,whereas
the pipe running INTO the rad was hot.

He reckoned there was an airlock that was causing the air in the bottom half of the radiator,thus making it warm.

He also pointed out to me that the boiler seemed to kicking in a lot quicker than it should be. (because the water going back to it is warm?)

We drained the water from the bottom of the radiator (bleeding it at the top didn't seem to make any difference),& re-filled the system & it indeed hotted up.

However,that's now three days ago,& the same symptoms have come back.
Hot at the top,warm at the bottom. The boiler seems to kick in every 10 minutes,even though everywhere else is piping hot.

So...I guess my question now is What would cause an airlock in the same radiator ( & same part of the rad) everytime?

Has the radiator had it? Is it is there some underlying problem?

Thanks for your help guys,at least i know it's an airlock now.