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

 

[jase158]

Can I just clarify what has been said,
1. radiator not working
2. heat is passing through when radiator disconnected and pipe placed instead
3. replace radiator and stops working
4. drain down from one side and radiator is working fine for a couple days then stops.
5. pipe work comes from attic across house and down.

my theory would be pipework, where is it coming from? does it connect to 22mm or 15mm pipe, is the pipework to radiator 15mm, 10mm or 8mm?

just seems like there isnt enough pressure to push water all the way through, when radiator is disconnected it is pushing it far enough, but when connected there isnt enough pressure to push it along. either that or partial blockage at joint that is blocking completely when heating is cold and when you are pushing heat through it is unblocking slightly.

the way I would go would be to find where radiator connects to rest of system and replace. or connect radiator pipework to somewhere closer.

water finds easiest route, so possibly passing straight past join and not going to your radiator.

 

[nick/matt1]

try replacing the trv. also ensure you hsve no restrictions on the return pipework, or partial blockage in the feed from the top up cistern, which can cause flow restriction

 

[PaulRB]

i wouldnt bother with a pump, your far better solving the problem. you say you drag water through the return, have you also tried it with the flow?
blockage, if the blockage is in the flow of course you can get water out of the return as theres no blockage there

can you re connect the flow or return closer the boiler (not both) reverse return system

I can't drain water from the flow pipe because the drain valve is in the return pipe.
If there is a blockage how can the hot water get thru the flow pipe when I drain from the return pipe?
When I do this, the rad works ok for 2/3 days!
Thanks

 

[fuzzy]

the water may not be coming from the flow pipe is my point, it CAN come from the return pipe

and you havnt answered my question, can you tee either the flow or return closer the boiler?

 

[PaulRB]

I think you're right. The problem is in the system before the rad but I can't get at the pipework there.
I just find it strange that I can get it working for 2/3 days before it packs up again.
As long as the water in the pipes is hot, the circulation seems to be ok.
The problem occurs as the water cools down.
I thought putting a small drill-driven pump in the return pipework might give the system the boost it needs to keep working.
I would only need to activate the pump for seconds, until the hot water comes thru again.
Thanks.

 

[PaulRB]

The hot water is definitely coming from the flow pipe because I can feel it coming down the pipe as I drain cold water from the return. It then circulates ok for as long as the heating is on. It seems that once I have the system flowing, it works ok but stops when the water cools.
Not sure if I can tee closer to the boiler.
Thanks

 

[nick/matt1]

would still look to balancing the system, and changing trv. The pipework after the rad is more likely the problem, unless as already stated there is a restriction in the feed

 

[JimField]

This is worth a try . Remove RAD close flow valve leave return open and close all other radiators.If this is a gravity system cap the vent pipe to the Fill and expansion,if a pressurised system no problem .Connect mains pressure to the heating system and open the return on the problem rad .The idea is to blow all the crap back out of the return pipe of this problemed area ,it may take some serious flow and keep pulling water off ,sounds like a bottle neck has become blocked and needs reverse flow to clear it. Hope this helps.

 

[jase158]

it seems to me that you are looking for an easy fix and imho there is no quick fix,

your options.

1. Put the pump on and AAV push the pump every few days, this will get the system running and like you say maybe when it gets hotter, you will not have to keep doing it, but if it is a blockage in the summer it will get worse. Remember to put 2 iso valves on there so it doesnt leak after you finnished and a iso valve on pipework that is being taken out so it doesn't just circulate in a circle.
2. Take floorboards/ walls up, replace joins and check for dirt
3. Get the system powerflushed and hope it is sorted by this (not sure this will work but might do)
4. Re-pipe the pipework so that it is connected to another rad

My opinion is get a proffesional in to do the work properly, get it fixed now and you wont have problems later

 

[fuzzy]

when hot it works when cold it doesnt. sound like a section is working on gravity and therefore the pump is missing the rad out as such. can you swap the tee for a swept tee

 

[jase158]

when hot it works when cold it doesnt. sound like a section is working on gravity and therefore the pump is missing the rad out as such. can you swap the tee for a swept tee

I was thinking something like that but didnt know it was possible, thanks fuzzy, learn something new every day

 

[nick/matt1]

this rad isnt run on when hot water only selected by any chance?

 

[stubob3000]

You definately need a permanent solution to this.....

There seems to be 2 major changes to the system since the rad hasnt worked (but did for 18 years?) A new towel rad and a new pump. I agree with an earlier post that the pump may not be as powerful as the older pump (so hot water is having a harder time trying to get to this lonely rad through longer than normal pipework over obstacles etc) If this is the case? Then if you tee this rads flow closer to the boiler you will be removing an awkward dead leg of pipework which may work??

But we need to also look at the other changes you have made since it stopped working... Can you remove the towel rad and place a temporary bridge between the flow and return (like you did in the cloakroom, using 15mm) Just to rule out the fact since this rad was installed with its new (but could be faulty) TRVs the cloakroom rad didnt work? worth a shot?!

The other major defect could be a possible blockage in the system (air or debris)? Again the original pump may have not had an issue....
The best fix is probably to power flush piipework to be on the safe side, although I would also recommend re-doing the flow and/or return pipework to rad?

Just a brainstorm here, but will the system all on max, including all TRVs and lockshields (and thermostats) to maximum WHERE exactly does the hot pipework stop? If you can feel around the system, along flow/return to the problem rad, where does the pipework stop being hot? If it is at a tee to the problem rad, then a swept tee (as suggested earlier) may work or the fact that this rads tail offs from the 2 pipe system are too long??

 

[nick/matt1]

could just be that the new towel rail is stealing all the heat and after a couple of hours the rad may kick in? Have you balanced the system?

 

[fuzzy]

if the towel rail replaced a previous rad its unlikely to be stealing heat as its probably a lower output

it may be more restrictive and with a less powerful pump it simply doesnt get there

 

[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.