Radiator problem


Postby paja » Thu Nov 25, 2010 3:55 pm

My house is only 5 years old and had no problems with my cental heating system before. After switching my haeting on I found out that one radiator stays cold.

I've tried bleeding the radiator but it made no difference.

My next step was closing other radiator valves with heating on but the faulty radiator stayed cold.

I've tried draining down the faulty radiator with heating on and then opening valves. Radiator will fill with hot water but it will cool down again after 30-60 minutes.

I've replaced TRV valve last night but it made no difference and radiator is still cold.

Drained the heating system filled back up again and bled all radiators but it's still not working!

I really don't know what to do next and don't want to call professional in as it's going to be expensive. Don't understand why won't it work as there is no obvious blockage because the radiator will fill up with hot water after being drained down. So if you have any tips PLEASE let me know.

Thank you
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Postby plumbbob » Thu Nov 25, 2010 5:37 pm

Make sure both valves to that rad are fully open then with the heating on, turn all the other radiators off so as to build up the pressure and force whatever is stopping the flow to move.

If this doesn't work, leaving the system full, you need to drain and remove the rad (or only drain it if you can get access to the pipes) and open each valve in turn and allow the water to flow into a bowl. Do this until it runs clear.

If necessary do this in stages giving time for the system to re-fill and not run the header tank dry. (Not a combi is it?)

The chances are one of the feed pipes is either clogged or airlocked.
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Postby paja » Fri Nov 26, 2010 4:40 pm

Thank you plumbbob. It's a combi boiler Alpha CD24C. Am I still fine to take the rad off and open valves?
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Postby plumbbob » Fri Nov 26, 2010 5:36 pm

paja wrote:Thank you plumbbob. It's a combi boiler Alpha CD24C. Am I still fine to take the rad off and open valves?


Yes but you need to be a little more careful.

Don't let the pressure fall entirely as this will introduce further problems so drain a bit, top up, drain some more, top up and so on.

Only drain off as much as is needed to make the water clear.

Make sure you top up with inhibitor to protect the system.

If the water you drain is very dirty, consider flushing the whole system and possibly fitting a Magnaclean to which will help to maximise the boiler life.
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Postby paja » Mon Nov 29, 2010 4:07 pm

Hi Plumbbob
I've followed your instructions even flushed the radiator to get rid of any sudge in it. Let the valves opened until I got clear hot water. But the rad will get hot only when both valves are fully open and all the other radiator valves are closed. With all rads on it stays cold.
Could it be my pump failing to circulate hot water around the house with all rads on?
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Postby plumbbob » Tue Nov 30, 2010 10:11 pm

paja wrote:Could it be my pump failing to circulate hot water around the house with all rads on?


Sure, a failing pump can't be ruled out, but it isn't the obvious culprit as all the other rads are getting hot and anyway, the boiler should sense the fault and show a fault light.

Is the cold rad the furthest from the boiler or is it at the end of a long pipe run? Is your system 10mm pipe (microbore)? If the answer is yes to any of these questions then your system may simply need re- balancing. ie, the water is being robbed by other rads.

Of course, the pipework could still be clogged or airlocked. The boiler bypass may be failing.

Have you checked the pump air bleed is open and the pump speed is set at 3?
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Postby paja » Tue Jan 25, 2011 12:35 pm

Thank you for your help Plumbbob
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