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