one Radiator not getting hot - a diagnosis (a paste)

[Fallingditch]

I was going to post a question on here about how to diagnose a radiator which had ceased getting hot, when I realised the question had probably been addressed in another place. Thanks @Nickfromwales

 

Posted 06 October 2013 - 07:02 PM

Hello,
I've got a towel radiator in the bathroom which has been cold for ages. We've had a plumber out who managed to get it working a while back however come the colder season we've put the heating on and noticed it's back cold. 

Initially I presumed the radiator was just full of air so bled the radiator. Air came out so I just assumed that was that. I topped the boiler up to maintain pressure. 

Unfortunately, that never really fixed it so I've been fiddling with the two valves at the bottom thinking one of them may have been turned off by accident (caught a towel on it or something daft like that) but to no avail. 

Another thing I've noticed is that the pressure has gone up again today after I bled the radiator (no air this time, was just trying to see if there was a constant flow of water which there wasn't!). I'm assuming that maybe there's some air in the system which has just 'expanded' with the heating being turned on. 

Anyway, I'm completely baffled by this. Any experts out there with any idea? Or can at least tell me which valves to fiddle with as they both seem to do nothing?! 

Thank you in advance  

#2jntabbycat

Posted 06 October 2013 - 07:12 PM

I had a similar problem with our towel radiator. Every other radiator was working fine except the bathroom one. I turned off the radiator after the bathroom one (the bathroom was second to last in system) and bleed radiator until tails were hot (meaning heat is getting in to it). I was actually told to turn off every radiator but the problem one but This would mean balancing the whole house again so just turned off radiators after the problem one in.

Im no plumber but hope that helps. If that doesnt work I have no idea  

 

Posted 06 October 2013 - 07:16 PM

I'm assuming that this system has a combi boiler (from the mention of pressure). The pressure rise would be normal if it's jut between the system when it's cold and when it's hot (mine increases pressure from about half way up the normal pressure range to about 2/3rds of the way up from cold to hot).

The chances are that either the system needs balancing or that the system has crud in it. If it's an old system that was working OK then the latter is a strong favourite.

To test things out, shut off all the rads except the towel rail, turn the heating on and see if it heats up. If it does, then the system may need balancing, if it doesn't, then the system has crud in it and needs flushing. 

#4222

Posted 06 October 2013 - 08:10 PM

jntabbycat, on 06 October 2013 - 07:12 PM, said:

I had a similar problem with our towel radiator. Every other radiator was working fine except the bathroom one. I turned off the radiator after the bathroom one (the bathroom was second to last in system) and bleed radiator until tails were hot (meaning heat is getting in to it). I was actually told to turn off every radiator but the problem one but This would mean balancing the whole house again so just turned off radiators after the problem one in.

I’m no plumber but hope that helps. If that doesn’t work I have no idea 

jsharris, on 06 October 2013 - 07:16 PM, said:

Welcome to ebuild.

I'm assuming that this system has a combi boiler (from the mention of pressure). The pressure rise would be normal if it's jut between the system when it's cold and when it's hot (mine increases pressure from about half way up the normal pressure range to about 2/3rds of the way up from cold to hot).

The chances are that either the system needs balancing or that the system has crud in it. If it's an old system that was working OK then the latter is a strong favourite.

To test things out, shut off all the rads except the towel rail, turn the heating on and see if it heats up. If it does, then the system may need balancing, if it doesn't, then the system has crud in it and needs flushing.

I've just turned all the radiators off bar the bathroom and also bled them all. All have no air in them. Interestingly, when I went to bleed the bathroom again, the water pressured dropped so much that water stopped coming out after a couple of seconds. 

The heating has been on for a couple of hours and the little bit of exposed pipe below still feels cold. This suggests to me that the hot water isn't reaching the radiator?

Anyway all radiators are turned off bar that one with heating still turned on so I'll let you know if there's any change. 

Thank you both for replying so quick. 

#5jsharris

posted 06 October 2013 - 08:32 PM

Sounds like there's a lot of air in the system that's now been forced into the towel rail. I'm assuming that you've topped up the system using the filling loop to get the pressure back up, but am a bit concerned that the pressure would drop so low from just bleeding a towel rail. This suggests that the pressure vessel in the boiler (or elsewhere in the heating circuit) may have lost charge pressure. Worth checking, as the pressure vessel should be able to hold the system pressure over a reasonable range of change in volume. It may even be that the diaphragm in the pressure vessel has failed, allowing a lot of air into the system.

You can check the pressure vessel if you have a car tyre pressure gauge and a suitable pump ( a bike pump with a Schroeder valve adapter will do). The procedure is to drain the system down to zero pressure and check the pressure in the pressure vessel with the car tyre pressure gauge (you should see a valve on it for this purpose). The pressure vessel will typically have 1.5 to 2 bar in it (the boiler manual will tell you the pressure). If it's reading less than the correct pressure, then pump it up with the bike pump, check it, then refill the system using the filling loop and valves.

Keep an eye on the system pressure, as it shouldn't change much, just go up and down a bit between hot and cold. If the system needs refilling from time to time the get the pressure back then it has a leak somewhere and this should be found and fixed. 

#6222

Posted 06 October 2013 - 09:46 PM

Just had a quick fiddle with the two radiator valves with the air vent open and I've managed to get water coming out at pressure. All other radiators off still. Strangely, the water is cold though? 

(Boiler pressure seems normal.)

Have had some issues with system thermostat this evening so perhaps purely coincidence and boiler has turned itself off. Would still have thought water would still be warm in pipes. 

Will have another look tomorrow. Thanks 

#7Nickfromwales

Posted 06 October 2013 - 09:47 PM

Hi,
Sounds like first thing to sort is the valves on the towel rad. You mention fiddling with them so how about at least confirming that they're fully open? Turn both valves fully anti-clockwise, untul they stop, then close them fully (clockwise) and count the number of turns. Then open them again (anticlockwise), and make sure it’s the same number of turns as needed to close them. This will prove if you have a knackered valve stem which isn't actually opening or closing the valve internally, as the number of turns between open and closed position should be the same. 
Flow to a towel rail is usually the cause of other rads not working as they offer little or no resistance so they often cause bypass issues, the exact opposite of your symptoms! How old is the Combi, maybe your pumps on its last legs? And how long do all the working rads take to get warm from the time you turn the heating on?
  

#8Nickfromwales

Posted 06 October 2013 - 09:49 PM

222, on 06 October 2013 - 09:46 PM, said:

Just had a quick fiddle with the two radiator valves with the air vent open and I've managed to get water coming out at pressure. All other radiators off still. Strangely, the water is cold though? 

(Boiler pressure seems normal.)

Have had some issues with system thermostat this evening so perhaps purely coincidence and boiler has turned itself off. Would still have thought water would still be warm in pipes. 

Will have another look tomorrow. Thanks

My reply crossed with yours. As I thought, your valves were slightly or fully closed, hence no air/water coming out until you 'fiddled' again :-) 

#9222

Posted 07 October 2013 - 05:47 PM

Nickfromwales, on 06 October 2013 - 09:47 PM, said:

Hi,
Sounds like first thing to sort is the valves on the towel rad. You mention fiddling with them so how about at least confirming that they're fully open? Turn both valves fully anti-clockwise, untul they stop, then close them fully ( clockwise ) and count the number of turns. Then open them again ( anticlockwise ), and make sure its the same number of turns as needed to close them. This will prove if you have a knackered valve stem which isn't actually opening or closing the valve internally, as the number of turns between open and closed position should be the same.
Flow to a towel rail is usually the cause of other rads not working as they offer little or no resistance so they often cause bypass issues, the exact opposite of your symptoms! How old is the Combi, maybe your pumps on its last legs? And how long do all the working rads take to get warm from the time you turn te heating on?
Regards, nick.

The valves do seem a bit dodgy, in that the turns aren't always equal. Sometimes it feels like you're just turning the knob and not the valve, ie it feels like it's not 'biting'.

I'm pretty sure at least one of the valves is open though as the water comes out of the bleed vent with pressure, however with the heating on the water is still cold? I have one other rad turned on and that is hot. I don't get how the bathroom one is stone cold when the water is clearly coming out with pressure??

The boiler was replaced with a Worcester Greenstar junior in mid 2007. When all the rads are turned on they take about 10/15 minutes to all warm up.

Thank you 

Edited by 222, 07 October 2013 - 05:47 PM.

#10Nickfromwales

Posted 07 October 2013 - 05:55 PM

Don't confuse pressure with flow rate ( circulation ). You can have pressure in one pipe only and you'll still get water out of the vent, and the same if its only on the other pipe as the flow and return circuit are linked at the boiler. Your problem is not pressure related, its flow and return circulation related. The valve that turns and turns is probably a dummy valve which gets set to the correct number of turns ( balanced ) and then the cap gets fitted after to stop people from turning the wrong valve for on & off purposes. Take the caps off the valves and actually turn the stems to prove operation as per my previous. 

#11jsharris

Posted 07 October 2013 - 06:25 PM

I think Nick's right, the LSV (lock shield valve) on the towel rail may well be closed. LSVs are internally the same as ordinary valves, but the cover is locked and doesn't turn the valve spindle internally (hence the name) you need to unscrew the cover from the LSV and turn the spindle fully open (using a spanner or the knob from an ordinary valve).

It's also possible for the valve sealing washer inside to get stuck in the closed position, with the valve shaft getting disconnected so that turning it doesn't do anything. 

#12Nickfromwales

Posted 07 October 2013 - 06:39 PM

:-)
It doesn't turn the spindle, but WILL turn infinitely. Hence my asking to confirm stop point and number of turns. The boilers a good un, and should deal with any pipework setup 22mm/15mm/10mm etc so I think opening these valves will sort the prob. Only open the lsv half way though, or you may experience problems elsewhere like downstairs rad far from boiler slow/not heating. The term balance is what your going to have to strive to achieve for correct operation, so no more fiddling lol, calculated adjustment is the new term for it :-))) 

#13222

Posted 07 October 2013 - 06:57 PM

I have removed the covers and turned as so:

  IMG_0872.JPG   50.86K   2 downloads


Rad still cold after 10 mins.

Thanks  

#14Nickfromwales

Posted 07 October 2013 - 07:17 PM

Tough nut to crack this one, but we'll get there. 

I’ll assume that the bathroom is on the first floor.

Close ONE side of every rad upstairs, if TRVs ( thermostatic rad valves ) are fitted, set these to * or 0, you don't have to touch the LSV (lock shiled valve) on the other side.

Next, with the boiler lit and burning for central heating, pressurise it to 2.5 bar and go to the towel rad. Close the left hand valve by turning it clockwise until it stops turning. Open the vent and let out water until the water is hot, not cool.

Re pressurise boiler to 2.5 bar and go back to towel rad. Open the left valve and close the right. Open the vent and let out water until the water is hot again. Upon getting hot water, open the right valve up immediately and check results. 

If there is a rad right by the boiler, turn that off too, as those closest to the boiler often steal the lions share of the pump potential. 

Give that a go, as that will purge, or pull through any air lock on the pipework to the TR. 

Edited by Nickfromwales, 07 October 2013 - 07:17 PM.

#15Nickfromwales

Posted 07 October 2013 - 07:24 PM

Just out of curiosity, did you have a Combi conversion done, or did you always have a Combi before the W/Bosch was fitted?
Some goons leave the original pipework as untouched as possible in the airing cupboard to do an "old to new" conversion, and many a time I've seen the original pump bypass valve still in the flow and return circuit, when it should have been cut out. The WB will have its own automatic, internal bypass. 

#16222

Posted 07 October 2013 - 07:40 PM

Ok, just closed left hand valve, and opened vent. Only a little bit of water came out and then it stopped. This suggests to me there's something wrong with right valve? 

I then went opened left valve, water came out but was not hot. Left for 2 minutes until it started to slow down. Checked boiler pressure and it's gone down to around 1 bar.

All rads are turned off in house apart from one which I can’t get to as I can’t be bothered to un-screw radiator cover. 

Can’t remember type of boiler before but there was no hot water tank and work was carried out by British Gas. 

#17Nickfromwales

Posted 07 October 2013 - 08:08 PM

Yup, time for some new rad valves and then go on from there I think. If other rads were hot, or boiler was trying to get heat out to the rad with the cover on, then you should have got some hot water out sooner than later. I think you may have an air lock there but it’s probably being caused by the lack of flow through the pipework to the TRV. 

Another good exercise, if you want to do belt n braces, would be to drain the heating, remove the valves (don’t bother looking inside or through them or trying them for operation, just chuck them in the bin) and link the two pipes together with some compression elbows (90's) and a short piece of pipe. Fill the system and run the heating. The pipework should get hot straight away and stay hot whilst all other rads are on and open and do so for the full heating on duration. 

This will prove without doubt that your pipework is ok. 

Next up of course, is to drain, fit some new valves, and retest for good operation. 
Any other questions about the above please repost and I’ll talk you through, other than that we'll hear from you when above has been carried out. 

#18Nickfromwales

Posted 07 October 2013 - 08:12 PM

One last thing!
Honest!
If British gits did the boiler change, did they fit a magnetic filter? Manga clean or little brass upside down bottle looking thing adjacent to boiler?
If so, are the valves on it fully open?
And are the flow and return valves under the boiler (on the far left and far right 22mm pipes) also fully open? Check and reply, as they can cause major flow issues if not fully open!
Brain hurts from thinking now so I'm out of ideas after that :-} 

#19222

Posted 07 October 2013 - 08:40 PM

All valves on bottom of boiler are fully open. I cannot see any external filters fitted. 

My plan is to drain the system at the weekend, remove the valves on the radiator and just cap the pipes off. Then fill the system back up again, bleed all radiators to get rid of air, and check the caps - If they get hot then I know there is hot water there. Does that sound ok?

Thanks for all you help nick 

#20Nickfromwales

Posted 07 October 2013 - 09:02 PM

Nope, DO NOT just cap the pipes, it'll prove nothing, link them like I've mentioned. You won't have to cut or alter pipework to do that so should be no extra grief. If the pipes aren't parallel then you won't get two 90's to link between, in this case put two 90's facing down, then two more 90's linking together, this will solve the awkward angle issue. 

 

#22222

Posted 07 October 2013 - 09:17 PM

Right ok I'll pipe the two outlets together. 

Will plastic pipe suffice? As I don't really have the equipment to be making copper joints etc

Thanks again 

#23222

Posted 07 October 2013 - 09:20 PM

Or how about even that flexible piping you can get? 

#24Nickfromwales

Posted 07 October 2013 - 09:39 PM

When you take the two valves off, you will be left with two 1/2" nuts and olives which are captive on the pipe. Don't try to take these off. 

You can use two flexis, or one if bends will allow, no problem at all. I didn't think of that :->

The flexis will come with nuts and olives on one or both ends, discard those and the male threads on the flexis will fit right on the nuts left on your pipes. 
Bingo. 

#25Nickfromwales

Posted 07 October 2013 - 09:40 PM

222, on 07 October 2013 - 09:17 PM, said:

Right ok I'll pipe the two outlets together. 

Will plastic pipe suffice? As I don't really have the equipment to be making copper joints etc

Thanks again

Compression fittings are made off with spanners/grips so no soldering needed at all. 

#26222

Posted 07 October 2013 - 10:06 PM

Thanks for all your help. 

I'll try and scavenge some piping together and hopefully get this sorted at the weekend and post back the results. 

Much appreciated  

#27222

Posted 15 October 2013 - 07:07 PM

I managed to fit the pipe over the weekend and it got hot as predicted. 

I've fitted the new valves this afternoon and they're holding well so thank you all for your help. Much appreciated!

I just have one final question regarding the valves and balancing. 

At the moment, I have one valve fully open, and the other half open. How would people advise on me setting the valves efficiently?

Thanks again  

#28Nickfromwales

Posted 15 October 2013 - 09:43 PM

Hi,
Good results!

To balance the towel rad, close the part open valve fully and allow it to go cold. Then open the valve 1/4 turn and feel for heat. If nothing, open another 1/4 turn. Repeat until heat starts to enter the rad and that's it. Towel rads heat with very little flow so try that and see how you get on.
Nick. 

#29222

Posted 25 October 2013 - 11:38 AM

Thanks nick. Your help is much appreciated  

#30bwelton

Posted 22 February 2015 - 02:59 PM

Hi, sorry to jump on this thread, but I have similar problems. 

I have now removed the towel rad and washed water through it with a hose to check it was nit blocked with sludge. Note I have also fitted Magnacleans and also cleaned out the rest of the system, but just have a couple of radiators left that I am not getting flow through. 

When I refitted the Towel Radiator I left the top bleed screw open and opens the Lockshield and also the main flow value to fill it up. Both produced positive pressure and pushed the air out the top vent screw. 

As the air was clearing, I let water come out of the top of the rad until I could feel warm water on both the feed and return. Great I thought !!!

However once I close the bleed screw and in theory have flow through the radiator, I found it did not warm up. 

I think I have tried absolutely everything but to no avail. 


Just a couple of notes on my system. 
- it's large, 34 heating circuits including 14 x downstairs underfloor heating loops. 
- the 20 radiators are on plastic microbore with copper tails out of the walls in to the rads for aesthetics. 
- the plastic microbore to each radiator come off 4 way plastic push fit manifolds in to 22m copper
- main boilers are 2 x Valiant Condensing boilers operating in Parnell to 34mm main circuits. 
- i have 2 other radiators that I have not got working in addition to the towel rad
Any ideas on how to get this towel rad working ?

Thx 

#31Nickfromwales

Posted 23 February 2015 - 07:19 AM

Hi,
Turn off one valve (TRV easiest if fitted ) on every WORKING radiator, and retry. 

It sounds like the other rads are acting as bypass. 

Try that and if the lazy ones haven’t come on in a couple of hours max then repost here and we'll continue the research 
Regards, Nick.

PS Do you know if the radiators have been balanced? 

[Nickfromwales]

"This was a public service announcement"