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Radiator hot at top cold at bottom. Whats wrong?


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#1 shenks1

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Posted 17 September 2007 - 07:58 PM

Hi,
1 of my radiators is cold at the bottom, but hot at the top. Whats the likely cause and how do I fix it?

#2 Guest_cwatters_*

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Posted 17 September 2007 - 08:22 PM

Sounds like it's full of sludge. Chances are some other rads are heading the same way. Have you been keeping the system topped up with corrosion inhibitor each year?

If the rad is a modern thin steel unit check for any corrosion/rust around the ends. If that's bad then consider replacing the rad. Otherwise drain system, remove rad from wall and flush out with hose in the garden. Consider doing other rads while it's drained. Refill and test, then if all ok then put the right qty of corrosion inhibitor in.

There are various chemical sludge removers and system cleaners you can try but if the system is really full of the stuff they may not work well and the dreaded "power flush" of the whole system maybe required.

Shop around for the best deal on a power flush. Some companies like British Gas have had a bad reputation for trying to charge £600 and hinting that they may refuse to cover repairs under their maintenance plan unless you agree to it. You can find it a lot cheaper if you shop around.

If you do have a BG contract then check the small print. I believe they charge for the first power flush after you sigh up but subsequent ones are free.

#3 shenks1

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Posted 17 September 2007 - 08:41 PM

Thanks for that. To be honest this is a pretty new system. New boiler, radiators but some old piping retained. It was supposed to have been flushed when it was fitted, by British Gas! It is covered, but I was hoping it was something simple I could fix without calling them in. I'll have to have a word with them, if you know what I mean. Thanks again.
Shenks1

#4 simon71

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Posted 17 September 2007 - 09:26 PM

have you bled the rad?

#5 Guest_cwatters_*

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Posted 18 September 2007 - 06:43 AM

I guess it could be gas but I would have thought that would make it cold at the top.

#6 siman

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Posted 18 September 2007 - 08:11 AM

Hi, does your radiator actually get "HOT" at the top, or just a bit warm? I only ask as I had one which did this and I assumed sludge. However, it wasn't "HOT" at the top, just warmer than bottom. Turned out the TRV was broken and there was only a trickle of water passing through the rad - enough to rise up and lightly heat the top but without heating the bottom (which was totally free from sludge and had me baffled when I removed it and found it to be clean and empty!)

It was just a thought... and worth checking before British Gas try and sell you a "gas softener" or something!!!

#7 shenks1

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Posted 18 September 2007 - 09:28 AM

Hi All, I've tried bleeding and it doesn't make any odds. I am sure the rad is hot at the top and cold at the bottom. The "management" has taken the decision to call BG in, so after they've been, I'll try to post thier explanation of the problem. Thanks to all for your suggestions.

#8 Guest_cwatters_*

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Posted 18 September 2007 - 10:08 AM

Do let us know how you get on with BG. I suggest you have a look for pricing on a power flush in your area while you wait for BG to turn up.

#9 ginfearsdad

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Posted 20 September 2007 - 08:21 AM

Hi,
I've got a similar problem. The pipe up to the rad valve (TRV) is very hot, but the rad only gets luke warm. Will I need to replace the TRV or is there a way of adjusting them internally? The valve itself is only a few years old.

#10 shenks1

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Posted 27 September 2007 - 12:58 PM

All,
Sorry I didn't get back quicker. I wanted to be sure it was cured, then I got distracted!
When BG came the guy said the system had air-locked. He turned all the other TRV's to off and the cold rad one to max, turned the master stat up for 10 mins and let it run. This has cured it!
Magic eh!

#11 ginfearsdad

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Posted 01 October 2007 - 11:14 AM

A nice City Link delivery man who used to work for BG told me my TRV was jammed. Working the pin up and down with pliers unblocked it and the problem seems to be solved.

#12 jos

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Posted 19 October 2007 - 10:16 PM

Hi - I had a completely new plumbing system (pipes, radiators, boiler, megaflow) installed 12 months ago, however 90% of the radiators are hot at the top but only warm at the bottom, despite the pipe to the TRV being hot. All have TRV's on them.

I've tried bleeding them, but that doesn't help.

I then closed all the TRV's when the heating was on and opened the radiators one by one, from the bottom of the house - this seemed to help a few of the radiators, but still the problem persists on the others.

I did notice that one radiator is hot at top and hot at the bottom - near the TRV, but hardly even warm at the bottom on the other end.

Can anyone please help?

#13 Guest_buildersmate_*

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Posted 20 October 2007 - 06:55 AM

If you are saying that you can get each single rad hot in the middle at the bottom by turning the others off, this suggests to me that the pump may not be beefy enough to pump water around the system.
However if you read the above postings first, you will know it could alternatively be black sludge. Do you know for sure that inhibitor was put into the system 12 months ago on commissioning? Did this problem occur last winter?

#14 jos

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Posted 21 October 2007 - 11:35 PM

Thanks for your reply. What i mean is that at all times all the radiators are hot at the top, however 90% of them are only warm at the bottom, the other 1 or two are hot at the bottom.

I think the radiators were hot (top and bottom) last winter, but can't be 100% sure. we have however had 2 extra small radiators added since then, so the system was drained etc.

I doubt inhibitor was added to the system on comissioning, should it have been? Could lots of radiators be full of sludge already?

#15 Guest_buildersmate_*

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Posted 22 October 2007 - 07:02 AM

Yes, it doesn't take more than a few months. Systems with steel rads (most are) must have adequate inhibitor in them.

#16 keepheat

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Posted 22 October 2007 - 09:27 AM

After 12 months the system water cant be that bad that a huge amount of sludge has built up. i may be wrong, i havent seen a buld up that bad before in that short time,

jos... I think its you, i notice also have posted about problems with your megaflow not heating up also
this must be linked with the rads not getting hot also.
are you sure that its all plumbed in correctly
you have added 2 radiators onto the system, where did you connect onto the system?
is your system a Y plan or S plan.
Y plan is a 3 port motorised valve.
S plan is min 2 x 2 port motorised valves or more.

Is the boiler temp low, med, high?
And do you have an AUTOMATIC BYPASS VALVE. check if you do have a bypass that its not open too much that it lets the heat go straight back to the boiler. IM THINKING THIS COULD BE THE PROBLEM.
You say the rads are weak, and the megaflow is also, but the pipes going into and comming out the megaflow are hot.
boiler pump, or bypass,

#17 jos

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Posted 25 October 2007 - 11:34 AM

Thanks - Boiler temp is 55 degrees. I'll check the system tonight and confirm on the other question.

If the system wasn't properly flushed on install, and no inhibitor added on install or after the 2 radiators were added in the summer - then I assume this could be partly the cause of the issue?

Also one radiator (top of system) is always needing to be bled - every week.

I appreciate your help!

#18 Guest_buildersmate_*

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Posted 25 October 2007 - 01:25 PM

Then that's a sure sign that corrosion is still occurring. The byproducts of corrosion are black magnetite (as discussed) and hydrogen gas. The gas collects in one (or more) of the top of the rads.