One cold radiator - draining didn't fix

[Apnomis]

Hi, I've got a problem with a radiator in the bedroom - it is stone cold, and the pipes leading to it and out of it are stone cold.

It is an old conventional open system and all the other radiators are working fine - including the other one in the same bedroom (the bedroom has two windows and a small radiator under each on the same wall). They are just standard on/off values and there is no thermostat.

I decided to drain the whole system, partly because of the issue with this radiator and partly because the system had become noisy and the radiators weren't getting as hot as they used to.

The cold radiator drained fine (which in my layman's world means the out pipe isn't blocked), and once I had flushed the system a few times and refilled with water and Sentinel X400 I bled the cold radiator and it filled back up with water (again suggesting to me there is no blockage on the in pipe).

After bleeding all the radiators I turned the system back on and all the radiators got really hot - much hotter than before the drain, and as a plus there was no pipe noise. However this cold radiator, despite filling up with water, remains stone cold, as do the pipes in and out of it.

I tried turning the pump up to max (level 3) just in case that made a difference, but it's still cold.

I don't think it is a balancing issue as all the other radiators are equally hot when all fully open. Also wouldn't you expect it to be at least slightly warm rather than completely cold?

I'm going to keep the X400 in for a couple of weeks before draining again and refilling with X100 and X200, but I don't really want to do this before I've fixed the cold radiator.

Has anyone got any ideas of what to try next? I don't really want to go to the expense of getting a plumber (I plan on replacing the whole system sooner or later) and although I'm a complete plumbing novice I'm not adverse to a bit of DIY with the right instruction...

 

[stem]

The cold radiator drained fine (which in my layman's world means the out pipe isn't blocked)....and it filled back up with water (again suggesting to me there is no blockage on the in pipe).

I'm afraid that logic is incorrect, when a system is being drained or filled with water it can flow via either pipe. After all, both flow and return are connected to the same boiler. It's only when a pump is circulating the water around the sealed system that a flow and return are established.

Try switching all of the other radiators off, and just leaving the problem one on. What happens then?

 

[Apnomis]

The cold radiator drained fine (which in my layman's world means the out pipe isn't blocked)....and it filled back up with water (again suggesting to me there is no blockage on the in pipe).

I'm afraid that logic is incorrect, when a system is being drained or filled with water it can flow via either pipe. After all, both flow and return are connected to the same boiler. It's only when a pump is circulating the water around the sealed system that a flow and return are established.

Try switching all of the other radiators off, and just leaving the problem one on. What happens then?

I've closed all the valves on the other radiators and they gradually went cold, the problem radiator which has both valves open stayed cold. However I have noticed there's a very slight moisture around the valve screw, not so much a leak more like condensation. It seems to be on both sides but it is worse on the left valve. Not sure if that is connected?

It's interesting what you say about being able to fill/empty it without it necessarily needing both pipes working - does this suggest a blockage in the valve or pipe? How could I check/test this?

Would it work if I closed one valve and bleed the radiator? Presumable if the other side if blocked the radiator would eventually run dry?

If there is a blockage how could I fix this without resorting to paying for an expensive system power flush?

 

[dominoman]

If you've closed off all the other radiators, and the hot water tank, and the radiator still doesn't get hot, then water isn't getting to it.

You've bled it, so it has to be a blockage.

If you can easily close the valve and the lockshield and remove the radiator then do that. Then open the valve (with a bucket handy) and see if water flows. Same on the other side. It could be as simple as a siezed valve.

Yes - you can do a DIY powerflush using mains pressure, but that would be a last resort for me. Sounds to me like it is a balancing issue still

 

[Apnomis]

If you've closed off all the other radiators, and the hot water tank, and the radiator still doesn't get hot, then water isn't getting to it.

You've bled it, so it has to be a blockage.

If you can easily close the valve and the lockshield and remove the radiator then do that. Then open the valve (with a bucket handy) and see if water flows. Same on the other side. It could be as simple as a siezed valve.

Yes - you can do a DIY powerflush using mains pressure, but that would be a last resort for me. Sounds to me like it is a balancing issue still

I closed off all the other radiators, but not the hot water tank...

I've tried bleeding it with both valves open and water spurted out, I tried bleeding it with both valves closed and the water soon stopped coming out. I closed the left valve and opened the right valve and water still didn't come out when bled, I closed the right valve and opened the left valve and water started coming out again when I bled it.

This suggests to my logic that either the right valve or right pipe is blocked?

I don't want to drain the system again until the X400 has had more time to work, but I will be draining it again in a couple of weeks to get rid of it. At this point I will be able to remove the radiator.

How would I know whether the blockage is in the valve or the pipe? Is it just a case of refilling the radiator with a hosepipe and seeing if it comes out the other end with the valve attached?

Hopefully it is just the valve as they only cost a few quid to replace and seems like a simple screw on operation, but what if the blockage is in the pipe?

 

[stem]

Are both radiator valves fully open? Has it ever worked? I'm just wondering if it's been piped up correctly.

 

[Apnomis]

Has it ever worked? I'm just wondering if it's been piped up correctly.

That's a good question and I'm not 100% sure if I'm honest as most of the time we have the radiators off in the bedroom. I'm pretty sure I would have noticed by now that it didn't work though as there have been occasions when it's got cold enough to want heating in the bedroom - I do have a vague memory of having them both on but it's been a while...

Both valves appear to be open (whether that's translating to the inside is another matter). I'm using an adjustable spanner directly on the valve on both sides so it's not as if the plastic tap is slipping or anything...

 

[Apnomis]

My wife clearly has a better memory than I have and confirmed it was definitely working when we last had it on last year.

 

[dominoman]

I've tried bleeding it with both valves open and water spurted out, I tried bleeding it with both valves closed and the water soon stopped coming out. I closed the left valve and opened the right valve and water still didn't come out when bled, I closed the right valve and opened the left valve and water started coming out again when I bled it.

This suggests to my logic that either the right valve or right pipe is blocked?

I don't want to drain the system again until the X400 has had more time to work, but I will be draining it again in a couple of weeks to get rid of it. At this point I will be able to remove the radiator.

How would I know whether the blockage is in the valve or the pipe? Is it just a case of refilling the radiator with a hosepipe and seeing if it comes out the other end with the valve attached?

Hopefully it is just the valve as they only cost a few quid to replace and seems like a simple screw on operation, but what if the blockage is in the pipe?

Yes, sounds like it is the right pipe (I presume that's the return pipe with the lockshield on it?).

There's no way to know if it's the pipe or the valve, but unless your system is really really sludged up I think it's 95% chance it's the valve.

Yes, best to wait until the system is drained anyway. Bear in mind the X400 will do nothing to fix this radiator, however long you leave it. It's a very gentle cleaner and in any case only works if it is flowing through.

 

[alan333]

I've just had a similar problem professionally fixed (some rads tepid plus one slow/cool). I'm a competent DIYer and I paid attention to how/what/why he did. My system sounds similar to yours with the small tank in the loft.

First was a powerflush, which collected a lot of gunk. This cured the cool/slow rads except one, which only worked if the other rads were off. Next was to figure out where the blockage was. He turned off both valves at the rad, and drained the rad into a tray/bucket. Then he opened each rad valve into a bucket (with the heating turned off) to see if either had a good flow. The return pipe had a good flow but the flow pipe didn't. To eliminate the actual valve he temporarily removed the valve from the pipe, and the pipe still flowed poorly. He then connected the flow valve to an air pump and blew back up the pipe a few times (with the water still in the system). You could hear the whoosh of the air blowing out in the header tank in the loft. After each blast he disconnected the air pump and allowed the water to flow back through, thus testing for good flow. The water coming out had quite a few small lumps in it. The flow was a bit better after blast 1, but really good after blast 3. He then tested the flow with the heating/pump turned on, which gave better flow again. He then re-fitted the pipes to the radiator and bled the system. I now have all rads working perfectly.

There was nothing difficult about what he did, and I'd have no hesitation to do it myself if necessary... now that I know what's possible. He didn't worry about taking valves off with water in the system etc - there's no pressure in the sytem and you can hold the water back with a finger.

The air pump he used looked virtually identical to this, he pumped up the pressure and let it go in one big blast...
http://www.pureadhesion.co.uk/silve...5-litre.html?gclid=CLzh0fv_yMMCFULKtAod8FQAKg

Hope this helps

 

[stem]

Or remove the radiator valve, connect a hose pipe with a jubilee clip to the pipe and a send a few quick blasts of mains water up it. Don't leave it on too long, otherwise the feed tank in the loft might overflow.

 

[Apnomis]

Thanks for the replies everyone. It sounds like my best bet is to wait for when I drain the X400 and take the radiator off completely.

I don't actually know whether it is is the feed pipe or return pipe that is affected as both sides have an identical valve! I'm still hoping it's just a valve problem because nowhere else is experiencing this problem.

I had already considered shoving a hosepipe on the end if it was a blockage in the pipe, didn't think about blasting air in there, but I might consider that.

Also just to clarify, I didn't buy the X400 to try and fix this radiator, I bought it because the whole system was performing poorly and was incredibly noisy and clunky. It's been at least 5 years since the system was last drained/treated and unless the previous owners decided to do it just before moving probably a lot more than 5 years. I also wanted to add some X100 and X200 but it seemed silly to do that before cleaning.

I can confirm that already the system is significantly quieter (the odd clatter rather than a continuous orchestra of noises) and all the radiators, apart from the problem one obviously, are running significantly hotter than they were. I wish I would have done it years ago, so if there is one good thing to come out of the faulty radiator it's that it's made me do a ton of research on heating systems and how they work!

 

[AlanE]

Drain this radiator then turn off both valves on this one.

With pump off, open one valve, leave open, and bleed, until you hear water flowing into rad. then close it. Now open other end and do same until water flowing. Open first one and fully bleed.

What can happen is air lock in one pipe will stop circulation but radiator will still bleed because water enters via other pipe.

This procedure will normally clear air from both pipes.

 

[Mikefromlondon]

OP, if you are suspecting it is the right side valve as you have correctly diagnosed problem logically, with the right side feed/ or /flow, however I hope you are not mistaking the knob on the right valve which may look identical to the one on the left, but inside it has no engagement with the valve stem, and will just turn freely though it may feel it is turning the valve stem, so pull the knob out to check it has a slot that engages with the valve stem, as your valve may not be actually turning whilst you spin the knob, one side is fitted with this free spinning knob to stop people upsetting heating flow balance, whilst the other side is used to turn a rad on or off. Some times it is easier to overlook simple things. I hope this may not be the case with yours, but you never know, further more you would have felt when the valve came to its end stop at either end when fully open or when fully closed. But just in case you overlooked.
Better still use a small spanner to turn the valve to ascertain that it turns, as the plastic cap may feel it is turning whilst it may be just slipping etc.

 

[Apnomis]

Ok guys now that the radiator is off I can confirm that it's not the valves. When I open the right valve I get a slow but steady flow of cold water (bit more than a trickle) so this is the return pipe. The other pipe gives a much stronger flow of hot water so is the feed pipe. Is this flow behaviour normal? Does it mean there is no blockage?

I'm going to flush the radiator with the hosepipe outside tomorrow to see if the two radiator is blocked.

Anything else I should try before reattaching the radiator?

I did notice the feed pipe spluttered at first and the water that came out was black (whereas everywhere else the water is a light brown colour as the system has been cleaned and flushed. Now the water runs the same light brown so does this suggest it was an airlock in the flow pipe all along?