cold rad

[PaulRB]

I have 1 cold rad in a downstairs cloakroom.
I have flushed it, tested the valves ( not trv ) and connected a hose from the o/side tap to each valve to blast any air-locks.
I have turned off all other rads and it still won't work.
I have replaced rad with a length of 15mm pipe and the pipe gets hot immediately! Put a new rad back on and it works for 2/3 days then fails.
If I draw 1/2 a bucket from the return pipe, hot water is drawn thru the flow pipe and the rad works for 2/3 days.
I know it could be a blockage, either air or sludge, but how come I can always draw hot water thru if I drain from the return pipe?
It seems as if there is something stopping the free flow thru the system which I can by-pass by encouraging the flow when draining.
I would be interested in advice as to what should be my next step.
Someone must have come across this before!!
Thanks

 

[dontknowitall]

The way this thread's going you won't need that radiator as it will be nearly summer ...

 

[067256]

PaulRB.....you are not alone.
I have the exact same problem as you but on my kitchen rad. I thought i was all alone with this problem!!
If i shut off all other rad lockshields eventually, and i say eventually the rad warms up but does not get HOT,so frustrating.
New rad and valves fitted ( no trv on kitchen rad), tried balancing, tried pump speeds, tried bleeding the air........water coming out of all rads when bled. Have drained system and refilled again....put in inhibitor. NOTHING!!!
return pipe is hot, flow is cold!
Even the plumber i called was baffled.
1 THING THOUGH,
With all the above done, i am getting a constant noise of flowing water at the boiler and also at the pump in the airing cupboard.
Boiler fires but only for about 30 seconds
PLEASE HELP.

 

[Halesowen1]

But he has said he has turned off all other rads, so it would have nothing to do with the towel rad. As with them all off it still dont get hot.

 

[trev69]

have you taken the automatic valve apart and checked the components inside the needle sticks in that aswell ,and peronally i would put a trv and lockshield on the rad

 

[trev69]

sounds like the pump in the boiler is dying on you

 

[nick/matt1]

could be scaled up. boilwer only fires for few minutes therefore heat is lost before radiator. it seems that as the return is hot and the flow is not, the valves could be the wrong way round... and causing restriction. either that or the pressure on the return is greater than the flow so it cant push round.

 

[PaulRB]

Ok guys.
I can't believe so many people are willing to think this thru and offer advice!!
Just to be clear; all rads have new valves, some are TRVs and others wheelhead.
I have fitted a brand new pump.
I have drained down twice in 48 hours and the water coming out of the system is lovely and clean.
Before fitting the new rad I fixed a hose from the o/side tap ( off the mains ) to both valves + blasted thru to try and clear air or blockages.
The pipework to + from the rad is in the 1st floor void between ceiling + floor.
It is a long horizontal run I'm sure + it could be an air lock. It doesn't "feel" like air though, because it doesn't splutter when I drain some water from the return pipe + air doesn't collect in the rad, which I would expect if it was being shifted by the hot coming thru.
It could be a blockage but I'm puzzled as to how the hot water can get thru + continue to work for 2/3 days.
I have taken a board up to reveal the pipework + turned the heating on, in the hope of feeling hot water in the flow pipe and establishing where, exactly, there may be an air lock or blockage.
However, I can only access about 4 feet of pipe, then it goes over a wall. The pipe is cold for as far as I can feel.
I'm convinced that the problem is
a) a long pipe run including having to go over the wall,
b) a tee joint that the hot water is by-passing ( but which I can't get access to without taking up carpets + floorboards + which I'm trying to avoid.
c) a lack of circulation caused by a + b

Now my plan is to drain the system and fit an automatic air vent in the horizontal pipework, hopefully solving the problem of air in the pipe.
At the same time, I was going to fit 2 full-bore iso valves in the vertical section of both flow + return pipes so I can later fit a towel rad with a heating element in, without having to drain the whole system and losing all the inhibitor.
I also thought it might be a cheap alternative to fit 2 tees in the vertical return pipe, connect a drill-driven pump between them and use it every 2/3 days to assist the circulation in the system.
I know that seems extreme but it might be enough to get us thru winter and the rad may work more continuously when the weather turns cold and we have the heating on longer.

Thanks again everyone and the more I discuss this, the more common this fault seems to be. It's nice to know we're not alone!

 

[PlumbBobBob]

is there a rad on the other side of the wall you could tee into doing away with the up and over pipe

 

[fuzzy]

im confused by what you mean 'return pipe'. i thought you said you dragged water through the flow pipe, which is it?

if its an air lock you need to drag water through the flow and then the return, they are both seperate pipes. this is how you get rid of an air lock, no need to auto air vent mate

it is either an air lock - if so fix as i advise
pump underpower - new pump
bi passing - new tee as i suggest or re pipe closer boiler for reverse return to 'even' pressures

 

[PaulRB]

im confused by what you mean 'return pipe'. i thought you said you dragged water through the flow pipe, which is it?

if its an air lock you need to drag water through the flow and then the return, they are both seperate pipes. this is how you get rid of an air lock, no need to auto air vent mate

it is either an air lock - if so fix as i advise
pump underpower - new pump
bi passing - new tee as i suggest or re pipe closer boiler for reverse return to 'even' pressures

ok rad has 2 pipes - 1 bringing hot water, other returning water to boiler. I think of them as the flow and return pipes.
There is a drain valve on the return pipe which I can use to drain about 2/3 pints.
This is replaced by hot water thru the flow pipe and, once I have some circulation, the rad will work for 2/3 days, until the water in the system cools. Then I have to drain again. ( obviously I can't keep draining so I'm looking into why the rad works for 2/3 days then stops )
I think you're right about the hot water by-passing the flow pipe but I can't get at the joint to put in a swept tee.
Not the pump - it's new + working fine.
Thanks

 

[nick/matt1]

reduce the flow toradiator which comes off the tee to allow flow through this rad

 

[Halesowen1]

YOU NEED TO GET A PLUMBER/HEATING ENGINEER OUT NOW AS THIS IS WORTHLESS.
Its down to something you have done whether you believe that or not. This cannot just happen for nothing, Fitting air vent wont do nothing, fitting tees and a drill pump is pointless.
It needs draining, putting drain off on this problem rad pipework, fit higher powered pump, fill back up, then turn every other rad off completely, if no heat still leave running and start draining from rad with hose, this will draw water around.

 

[dontknowitall]

I'm beginning to wonder if the flow and return to/from the radiator have both been plumbed into the flow (or return) on the heating circuit.

 

[Halesowen1]

Plus this tee wont do anything, if no water will get round with others all off it aint gonna do anything.
If it all worked OK before then the system needs getting back to how it was.
You do not know if pump is working OK, just because its new means nowt.
Get a more powerfull pump. If you cannot draw heat to this rad with others off its circulation problem, be that air (no), This tee you have been told (no as it was fine before), Maybe faulty rad or pump causing obstruction of flow or not enough power to feed rad.

 

[Halesowen1]

When you have eventually been getting heat from this rad after removing and putting a link between, have you then gone to all other rads and just opened them up??
As I feel it is pump and when you open them back up again it is just easier for the water to flow around these other rads that are piped closer. balance the system correctly after getting heat to it.