DIY Doctor UK DIY Forums

Hello All,
Firstly, happy new year to all!
Secondly, We have a problem with a 1.5 m tall column we added in the spring last year, which is not heating up when the rest of the system is. The boiler is a Combi Greenstar 42cdi and there are 9 radiators in the house including the new one.
Last night I shut down all the other radiators and removed the trv tops to fully open the valves on this radiator. After 15 mins we noticed that one of the 5 columns and the bottom horizontal bar was heating up, but then did not improve. The TRV valves are not jammed, I have tried bleeding the radiator, but all that comes out is cold water.And the pressure has been topped up to 1.5 bar.
The radiator is situated on the ground floor with the nearest radiator to it working perfectly.But the flow and return pipes from this radiator to the next one are cold.
The boiler has been changed from a conventional a few months after the radiator was added.
Is this a flow problem caused by not enough pressure in the system to push the water up the radiator? If so can we increase the pressure on the boiler?
Or is the radiator not compatable with a combi boiler?

Lots of questions! Thanks in advance

Creeky

Happy new year to You CB.

Firstly I would say that your W/B 42kw boiler will handle the load you say including the column radiator. The flow rate from these boilers is driven by a 15/60 pump which should satisfy your need. In that you have closed all other radiators leaving the column valves open without success I would suspect the piping to the radiator may be the problem. Try bleeding the column with the lockshield closed and the TRV open and see if the water continues to flow from the bleed valve, give it a minute or so, and then try the same with the TRV closed, this will prove both flow and return pipes are clear. It would be helpfull to have someone at the boiler topping up during this test. Leave the boiler switched off.
The pressure in the system does not affect the circulation it only lifts the water to cover the high point of the system eg. 1.5 bar will fill the system to approx 35ft.

Hi Deearr2

This may be slightly off-topic, but I have to reply - YOU ARE A SAVIOUR!!!

The story - in case it may help others, and apologies for length, but I find detail helps...

Large room, 2 radiators. One had been getting colder and colder until it stopped heating altogether. The other not as hot as it should be. Both refurbished cast iron radiators fitted with lockshield and TRVs (Westherm) about 12 years ago, all valves fully on ( I say 'on' not 'open' as you will see...).

I have posted previously about the problem, and the best answers suggested a blockage or an air lock. I was seriously considering shutting down the whole system (17 radiators - biggish house!) and 'unplumbing' the affected area to do a belt-and-braces job.

It was your comment about shutting down the lockshield and TRV alternately and bleeding the radiators that did the trick! Never thought of that...

TRV shut and lockshield open - bleeds fine.

Lockshield shut and TRV open - hardly a drip.

Ergo it HAS to be the TRV (or conceivably still a blockage at TRV end).

The middle of the Westhern TRV has a wee triangular pointer indicating on the scale. Push that down, (WD40 if necessary!) and the head of the TRV can be completely unscrewed, leaving the base of the TRV unit still attached to the radiator.

What I didn't realise was that you can undo the nut (it's a knurled surface rather than a 6-sided nut) and remove the base of the TRV without flooding the house!

This exposes the wee pin that controls the flow, and guess what? Bit of green residue round it, and no movement when pressed. Bit of WD40, leave for a few minutes, apply grips CAREFULLY to the top of the pin, and ease up gently. BINGO! Further scoosh of WD40, ease up and down CAREFULLY with the grips, and soon it's loose enough to respond to pressing with a thumb.

Replace all the bits, giving everything a good scoosh of WD40, and now 2 roasting hot, controllable radiators.

I'm no longer frightened to play with TRVs, and thanks a million!

Jack.

Thanks for the reply DEEARR2, Apologies for not getting back to you sooner. Will give your suggestions at try at the weekend.
While I was waiting for your reply to be moderated I removed the radiator and flushed out with a hose pipe. Put back on again. Now the radiator gets warm but only at the top. The bottom horizontal bar of the radiator gets hot as well but the lower parts of the vertical bars are cold.

I will try what you have suggested and get back to you.

Thanks again

Creeky

Hi,
Me again. I tried your flow test DEEARR2 for each flow and return pipes by locking one off and bleeding with the other one open, then swapping over. Both pipes flow ok I got a good steady floe out of the bleed valve on both.. So I guess the supply pipes to the radiator is ok. While I was doing this I have noticed a small leaky joint on the radiator before the problem one. I will fix this on staerday morning. Do you think this could be causing the problem?

Also the radiator is from B & Q so one of the cheap 'Designer Rads' as they call them. Do you think this could be faulty?

Thanks again

Hi Creekybones

I'm wondering if your system is single-pipe (rather than double-pipe)? If you don't know, there's plenty of info here and on the web about the difference, but re-post if you get stuck.

If it is a single-pipe system, it's a problem I have come across and seems to defy the laws of physics - rather than have the hot water rise into the radiator and then go out the other end, the hot water just rushes past on to the next radiator.

It could be sludge blocking the radiator, or in this case with a new radiator, sloppy installation leaving bits of PTFE tape and other crud inside the radiator. Although it bleeds OK, that doesn't necessarily mean it's completely clean inside. Might be worth removing it to check - shut off valves both ends and get a radiator removal kit, or lots of shallow containers and old towels!

I have seen instances of the pipe being 'nipped' between the tee-joints to provide some resistance and so force the hot water up into the radiator, and also a valve being installed instead of a 'nip' to do the same job, but I would be frightened the valve could get almost completely closed, with disasterous consequences!

You mention increasing the pressure - I'm no expert on fluid dynamics, but why not try REDUCING the pressure (most pumps have two or three speed settings) - this might reduce the speed of the water flow, and help to stop it rushing past the offending radiator?

But this might reduce the efficiency of the rest of the system...worth a try though, as it only takes minutes to do.

I'd be interested to know how you get on - please post a reply when fixed!

Jack.

Thanks for the reply Jack.

The sytem is a 'Double Pipe' system and used with a combi boiler. The Boiler was replaced last year. I agree with the possiblility of it being blocked. I have taken the radiator off once already and flushed it with a hose pipe, which it now seems to be a bit better, but the bottom of the radaitor is still cold, and the top takes ages to warm up. I have a pressure washer so might put that through it to confirm its clear. When the boiler was installed (by a friend Gas fitter, Hes a good guy but very busy at the moment because of the cold weather so dont like to hassle him), He fitted a 'Magna Clean' so I would hope the system is kept clean, I have cleaned the magnet the other day.
I have fixed the leak today so the system has been drained an re-filled, but the column rad is still the same. All the rest are ok.

As the boiler is a Combi I was under the impression the pump only had one speed, But if I'm wrong let me know :)
I'm not keen on nipping the pipe as knowing me I will create a hole in the pipe!

Thanks for your help Jack, Will let you know how it goes

Regards

Creeky

Hi again Creeky.

I'm starting to feel just as involved in this project as you are! Determined to get a result...!

I confess I've never used a combi boiler, but I assumed that the circulation pump wouldn't be any different from any other system...be good to know if there is a difference for future reference.

Couple of points:

Not being insulting, but have you checked (if you can) that the valves at both ends of the problem radiator are operating 100% - especially the dreaded TRV if you have one?

There's much talk in here and elsewhere about balancing the system. A lengthy process, methinks, but you could short-circuit the process by turning off all other radiators except the one in the system that always has to be on - usually bathroom, and probably doesn't have easily accessible valves.

That means the boiler should only have to 'power' 2 radiators, and both should be hot. If not, I'm guessing there is a blockage. But that's surprising given your Magna Clean. Was there a lot of gunge on the nagnet?

If you're going to try cleaning out the radiator again, I wouldn't bother with a pressure hose - the force of the blast is dissipated inside very quickly - I doesn't magically scour the entire inside, so best just to use a standard hose connected to whatever tap gives you the highest pressure. And apply the hose to both ends of the radiator in turn, giving it a good shake while you do it. Any rattling sound will herald a major problem!

Waiting with anticipation for the next instalment...

Jack.

Thanks Jack,
I have ran the system with all the other rads closed but still does not heat up, the horizontal rail at the bottom gets hot and the top half of the vertical rails get warm but the rest is cold The Magna Clean was'nt too bad, its been in for nearly a year now and has been clean 3 or 4 times. The valves appear to be fine, the TRV is reversable, Both valve buttons move ok, and I have run the rad on its own with both tops off.

Thanks

Creeky

This is driving me crazy now!

The only other thing I can think of is to try bleeding it for quite a while (with suitable receptacles) just in case there is an air lock in the radiator.

I'm assuming you have a conventional header tank arrangement (or an equivalent for the combi system which is a strange animal to me) for replacing the water you bleed out...

Other than that, a long shot is faulty manufacture with something blocking the columns - any spare radiators (from the garage, dump, or someone replacing theirs) that you could try in it's place as an experiment?

Jack.

Will try the bleeding again, but I agree with you, it may be an issue with the radiator itself.
Will post back with any developments

Thanks for your help

Creeky

Using the normal bleed valve will not remove any airlock because the volume of flow is insufficient. To succeed, you need to remove the whole blank plug and drain serious volumes of water. Switch off both valves and remove one of the 1/2" plugs from the top of the rad. Connect a hosepipe or other pipe and direct into a bucket. Open one valve fully and allow all the water to flow until the pressure is lost.

Re-fill the system and repeat with the other valve. Replace the bung, re-fill again and bleed the rad as normal.

Doing this will a) remove airlocks, b) remove debris blocking the feed pipes and c) ensure the valves are working correctly and the water can flow.

If this fails, turn every other radiator off in the house fully. Does it get hot now? If it does not, the radiator may be plumbed incorrectly, ie, both tap offs from a the feed or return.

Good luck

thanks Plumbbob,
Will try your way of getting the air lock out and get back to you. The Rad is plumbed correctly as you can see where the pipies feed from under the previous radiator.

Will get back to you in a few days

Thanks again

Creeky

creakybones, curious if you fixed this. I have just googled for the same problem. My tall 5 bar radiator was fitted a month or so ago and only 1 bar and a bit heats fully along with the top and bottom horizonal . Everything else in the house works fine and have tried the isolating to just this one.

I had my boiler serviced today so the heating was on for a while, the service chap thought the most likely problem was that the holes from the horizontal to the verticals in the ones that won't heat could be blocked.

I called the company I bought if from and they are sending a new radiator for me to try, there was no questions really asked just told me it was possible, si I guess I'm not the first to call. It was real agro fitting it in the first place and i will have to call the plumber back at my cost I guess to swop it. It was agor for him so I don't think I can do it myself.

Well you have just reminded me to do this Job before the winter!! We decided to leave it in for the summer as we had too many other things on :). I will be interested to hear how you get on though, so we can proceed with our one.
Sorry I couldn't help

Creeky