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

 

[Leadbetter]

Take the rad outside and blast cold mains through it with an house pipe, is it an old system / old rad?

 

[PaulRB]

Take the rad outside and blast cold mains through it with an house pipe, is it an old system / old rad?

Thanks for the reply.
Did that with old rad but made no difference.
Put a length of 15mm pipe between valves and hot flowed as normal so thought it must be the old rad.
Bought new rad and installed and it got hot immediately, worked for 2/3 days and then packed up.
I've been told it could be air building up over 2/3 days and I thought of putting in an automatic release valve but I'm not sure where in the flow pipe I'd put it!
Frustrating because it works every time with the 15mm pipe and that's just a small rad!!!

 

[jase158]

try flushing out with hose again, could be that the sludge is building up in this rad, Automatic air valve would look a bit weird coming from radiator. Can get automatic bleed valves for radiator I think. have you tried bleeding radiator?

 

[PaulRB]

try flushing out with hose again, could be that the sludge is building up in this rad, Automatic air valve would look a bit weird coming from radiator. Can get automatic bleed valves for radiator I think. have you tried bleeding radiator?

Yeah I've bled the rad and the automatic valve was to go in the pipework in the ceiling ( the highest point ).
I've now had a mate suggest its not sludge or air but a "cold water barrier" stopping the hot water getting thru.
He's suggested turning the pump round the other way to see if it dislodges the cold water. Don't know if there are consequences doing that but I can see where he's coming from.
It's so frustrating because if I take off the rad and replace it with 15mm pipe the pipe gets hot immediately!!!
I'm wondering whether to put a piece of pipe between the flow and return pipes, with a valve in, below the rad. In effect, short-circuiting the rad.Then when the pipe gets hot, turn off the valve in the pipe so the hot water has to go thru the rad.
Seems like a lot of trouble but I'm beginning to clutch at straws.!!!

 

[AWheating]

what type of system is it? what is the water in the system like? is the radiator near/far away from pump? is the system balanced correctly? what pump do you have and is it set on max?

sounds like air lock/problem.

 

[fuzzy]

if valves work, no air, rad clear it is circulation fault, is it 2 pipe system, balanced properly etc, check all connections and valves and then shut down ther rads to try to force round, if it goes round u need to balnce

 

[PaulRB]

what type of system is it? what is the water in the system like? is the radiator near/far away from pump? is the system balanced correctly? what pump do you have and is it set on max?

sounds like air lock/problem.

Gravity fed open vented system.
Ignore balancing because if I turn off all other rads, it still doesn't get hot!
Pump is new and identical to old pump, set to max.
Water in system is ok, fernox added and nice and clean when I drain some.
I know it seems like an air-lock but I don't understand why hot water comes thru ok when I remove rad and replace with 15mm pipe!
I like the idea that it could be a "cold water barrier" stopping the hot coming thru because I don't detect any signs of air when draining it. Also, the rad works for 2/3 days until the water in the pipe feeding it gets cold again.
Is there a problem with turning the pump around ( even for a short time ) so reversing the flow in the system, to see if it works by having the hot water coming thru the "return" pipe and pushing the cold water ahead of it in the " flow" pipe?
The TRV's I have are bi-directional so I can't see a problem there.
Thanks
?

 

[PaulRB]

if valves work, no air, rad clear it is circulation fault, is it 2 pipe system, balanced properly etc, check all connections and valves and then shut down ther rads to try to force round, if it goes round u need to balnce

New valves and pump.
Agree with circulation problem, now I need to solve it!
2 pipe system.
Would turning the pump round and reversing the flow be ok?
Thanks

 

[fuzzy]

bi directional trvs can still stick in off position

dont turn pump round shut off other rads and see if it gets round

 

[Halesowen1]

Where does your friend suggest this cold water is??

Is the system 15mm to rads or microbore? has this rad been joined onto existing system?
It sounds like a problem with the pipework, either a long draw off to the rad or it has been bent, squashed causing a restriction of flow.

 

[PaulRB]

bi directional trvs can still stick in off position

dont turn pump round shut off other rads and see if it gets round[/

Thanks, tried that, no luck.
Been told to turn pump down as it might be pushing hot water past the joint before it has a chance to enter pipe.
Gonna try that now.

Also, I will try putting in an automatic bleed valve in pipe at highest point, in case it is an air-lock.
Running out of ideas. Hoped someone else had come across a similar problem.

Thanks

 

[PaulRB]

Where does your friend suggest this cold water is??

Is the system 15mm to rads or microbore? has this rad been joined onto existing system?
It sounds like a problem with the pipework, either a long draw off to the rad or it has been bent, squashed causing a restriction of flow.

15mm.
The pipe run looks to be quite long. I can't see it all the way because it passes over a wall about 4 feet away.
The pipe is under the floor at 1st floor level, it then drops vertically to a rad in a downstairs cloakroom.
We think the cold water is in the long horizontal run below the floorboards.
I don't think its an air lock, but just in case, I'm going to drain down the system and fit an automatic air vent in the pipe because there's nothing to lose.
I've turned off all the other rads and felt the 2 pipes ( flow + return ) to see if they warm up.
The flow pipe remains stone cold + the return warms up slowly ( I think its just the water flowing thru the system gradually heating up the water in the pipe from the other end )
When I drain off 4 pints from the drain valve in the return pipe, the flow pipe gets proper hot and the rad works for 2/3 days.
Its as if the drained water is replaced by the cold water in the flow pipe, closely followed by the blocked hot water.
Then when the system cools, the cold water blocks the hot again.
It's an existing rad ( now replaced with a new one ) that worked fine for 18 years. Coincidentally, I drained the system down to replace a bathroom rad with a towel rad, and that's about the time it stopped working.
No damage to pipework.

Thanks

 

[fuzzy]

its not a 1 pipe system so dont see how it can pump past the rad? youve tried shutting down all other rads and it didnt work but youve pulled it through return and it does? youve altered the towel rad and it stopped working? this is puzzling? is there a trv on the towel rad? is the rad linked from/to the towel rad? could it be the trv shuts down both rads? this could be so if piped wrong

is there a cylinder on the system?

 

[Halesowen1]

I still reckon it is a badly balanced system.
You have definitely tuned off all the other rads? Do the rads have TRV's fitted?
Seen a similar problem dozens of times and 99% are badly balanced systems due to dodgy pipework and long runs, the other 1% is due to a blockage causes mainly by bent or squashed pipes.
The way I would be doing this is to make sure every rad is off at the lockshield valve not TRV, including hall rad if its got 2 x Lockshields. This almost always sends water to cold rad, then you need to balance the system accordingly. Just opening them all back up will not sort the problem out.
It could be air gradually building up and blocking it up, air will always rise to the top so the thing to look for is where the pipe goes up over something then back down. imagine the pipe going over a door frame. This could happen if a new pump has been replaced, the old pump may have been powerfull enough to keep pushing the air around the system.

 

[fuzzy]

yes the smart money is on badly balanced which can be enhanced by badly piped

but if he has shut off all the other rads?

 

[PaulRB]

bi directional trvs can still stick in off position

dont turn pump round shut off other rads and see if it gets round

Done that and flow pipe still doesn't get hot.
Seems like I need to drain water from the return pipe just to encourage the hot to come thru the flow pipe.
Once the rad heats up it stays working until the system shuts off + the water in the pipes cool down. Then I need to drain water to get it started again.
Gonna try draining down and taking out a piece of the flow pipe,( as high as I can ) replacing it with a "T", and fitting an air bleed valve on the arm of the "T". Just to satisfy myself that it's not an air-lock.
I've also tried turning down the pump in hope that a lesser force will give the hot water more chance of entering the flow pipe,( rather than by-passing it ) but that hasn't worked.
If all else fails, I'm going to buy a towel rail with a heating element in it!!!
Thanks again, keep the ideas coming.

 

[PaulRB]

I still reckon it is a badly balanced system.
You have definitely tuned off all the other rads? Do the rads have TRV's fitted?
Seen a similar problem dozens of times and 99% are badly balanced systems due to dodgy pipework and long runs, the other 1% is due to a blockage causes mainly by bent or squashed pipes.
The way I would be doing this is to make sure every rad is off at the lockshield valve not TRV, including hall rad if its got 2 x Lockshields. This almost always sends water to cold rad, then you need to balance the system accordingly. Just opening them all back up will not sort the problem out.
It could be air gradually building up and blocking it up, air will always rise to the top so the thing to look for is where the pipe goes up over something then back down. imagine the pipe going over a door frame. This could happen if a new pump has been replaced, the old pump may have been powerfull enough to keep pushing the air around the system.

Ok I'll give it another go and I'll try and fit an air bleed valve of some sort as high in the pipework as possible.
Thanks again

 

[fuzzy]

dont see how it can be an air lock unless theres a leak or wrong vent inlet position, bu if you say it worked before there must be an issue with what has been altered surely?

 

[PaulRB]

dont see how it can be an air lock unless theres a leak or wrong vent inlet position, bu if you say it worked before there must be an issue with what has been altered surely?

The only change I've made is to remove a bathroom rad + replace with a towel rad. I fitted one side to the existing pipework.
The other side had to be altered to line up with the rad. So I cut the pipe + extended it by 150mm. That's all.
Can't see how that would affect the other rad. They're not directly connected and I've tried turning off the towel rad to see if it helps.
I will drain down again + fit an automatic air-vent in the horizontal run in the ceiling leading to the rad. At the same time I'm going to fit 2 full bore in-line isolating valves in the flow + return pipes, so if I have to work on the rad, at least I won't have to drain down the whole system.
Thanks for all the help, I'm sure we'll solve it in the end.

 

[PaulRB]

I was wondering if I could put 2 tees in the return pipe. Have 2 flexible hoses coming off the tees connected to a drill driven pump so that, when the rad stops working, I could encourage the circulation by helping the flow thru the rad.
I know it seems like a lot of trouble but I'm clutching at straws here!
It seems as though I just have to get the hot water started and the rad will work for 2/3 days, so a little boost in the system every 3/4 days is better than a cold rad all winter!

 

[fuzzy]

The only change I've made is to remove a bathroom rad + replace with a towel rad. I fitted one side to the existing pipework.
The other side had to be altered to line up with the rad. So I cut the pipe + extended it by 150mm. That's all.
Can't see how that would affect the other rad. They're not directly connected and I've tried turning off the towel rad to see if it helps.
I will drain down again + fit an automatic air-vent in the horizontal run in the ceiling leading to the rad. At the same time I'm going to fit 2 full bore in-line isolating valves in the flow + return pipes, so if I have to work on the rad, at least I won't have to drain down the whole system.
Thanks for all the help, I'm sure we'll solve it in the end.

is it a trv on the rad? if so it could be faulty, i always use manual valves on towel rails

 

[PaulRB]

is it a trv on the rad? if so it could be faulty, i always use manual valves on towel rails

The rad that won't work has 2 wheelhead valves on--brand new. The rads with TRVs on are all new valves.
Sure it's not the valves because I've replaced them all. New rad too.
I think its a combination of a long pipe run, having to flow up and over a partition wall.
It might still be an air-lock but it doesn't feel like it. When I drain 2/3 pints from the return pipe there is no spluttering or air in the top of the rad.
I will drain down and put an automatic air release valve in the long horizontal run anyway, just in case.
I'll also put in 2 full-bore isolating valves in the flow + return pipes at the same time, so I don't have to keep draining down the whole system.
Any advice on my idea of fitting a drill-driven pump in the return pipe, to assist with the circulation.
I get the feeling that if I can get the circulation going and the hot water thru, the rad will continue to work for 3/4 days before I'd need to help it again.
It might even work continuously once the weather turns colder and we have the heating on longer and every day.It only stops working at the moment when the water inside cools right down.
Thanks again.

 

[dontknowitall]

If there's an up and over section (partition wall) does the pipe have a bleed point there?

 

[fuzzy]

i wouldnt bother with putting a drill point on, easier to find a permanent solution

the up and over sounds the obvious problem area, do you draw water from return only? try the same with the flow.

can you redirect the flow or return? leave one connected at the same point and move one connection closer the boiler?