Central Heating / Radiator Issues


Postby nav122 » Fri Jul 25, 2008 9:22 am

Hi.

I flushed out my Central Heating system, as there was a lot of brown sediment at the bottom of the F/E tank (Rust deposits). Anyway once drained and cleaned, I filled up the F/E tank and added a cleaner. Once done I started up the central heating.

All the rads upstairs heated up - I then diverted heat away from the upstairs rad towards downstairs. Then 2 of the rads downstairs in the dining room and hallway heated up fine. I then evened this out with the rads that worked and the 2 downstairs still worked. There are 2 rads in the lounge and cloakroom that are still cold.

Initially I thought there was an issue with the pump (heating upstairs but not downstairs), but if there was it wouldn't heat the downstairs radiators.

My suspicion is there maybe debris stuck in those 2 rads. Is it worth draining the whole system again and filling up (so the pressure pushes any debris out) or remove the rads that don't work and hosing them out?

I have even tried to divert heat via the rad valves only to those 2 rads and switched the others off but no luck

My system doesn't appear to have sludge.

Any suggestions!
nav122
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Postby htg engineer » Sat Jul 26, 2008 7:57 am

Sounds like an airlock. Notorious especially if 8mm or 10mm pipe.

If you try draining and refilling - you're going to have to re-dose the system cleanser. Draining and re-filling does soemtims work.

Check the radiator valves to the problem radiators are open. Try turning off all but one the problem radiators off, see if it will push through. If you have access to the pump - turn the pump speed up.

Still no luck - remove the radiators, open the valves and drain into a bucket, you will probably hear the air come out of the pipes, replace radiator and vent.

Will watch for further posts, not really a problem as the weather is pretty good at the moment. Good time to cleanse and add inhibitors, not sure why everyone seems to wait until winter - then panic when they have no heating.

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Postby nav122 » Sat Jul 26, 2008 9:04 am

Thanks htg.

Yes we do have thin pipes going to the radiators. Decided to leave the flush in the system for about 14 days and then will drain it.

From your post i take your saying switch off all radiators that work, and switch on the one that doesn't and set the pump to max to see if this does anything..right? Tried this already but will give it ago again.

Your other suggestion I take requires removing the rads...? Or loosing the bolt between the rad and rad pipe - the big hexagonal one - and letting the air out rather than total removal?

Also if i systematically bled the system over the next few weeks wouldn't that get rid of the air?
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Postby nav122 » Sat Jul 26, 2008 9:55 am

Also, is it advised to leave the cleaner in the system for 14 days or so even though there is an airlock? Will the airlock not accelerate corrosion?

The other thing that is baffeling me is the rads that are cold, when drained via the draincock the waterflows out of the pipe but it is cold. If it was hot then I would know that there is something wrong with the rad? Is the draincock pipe side of the rad with the wheelhead valve the outlet pipe? Why is this cold - surely its not getting a feed from the heated water!
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Postby htg engineer » Sat Jul 26, 2008 2:28 pm

"The other thing that is baffeling me is the rads that are cold, when drained via the draincock the waterflows out of the pipe but it is cold"

Where is the drain off ? on the rad valve or on the pipework ? if the drain point near the radiator you will have to drain the water in the pipework from the manifold to the radiator - there will be a fair bit water - leave for 5 -10 mins and you will get hot water.

For 14 days the airlock should not accelerate corrosion - but the system cleanser is not circulating through 2 radiators and associated pipework, so you're only cleaning part of the system.

"From your post i take your saying switch off all radiators that work, and switch on the one that doesn't and set the pump to max to see if this does anything..right?" that's right - sometimes works.

htg
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Postby nav122 » Sun Jul 27, 2008 12:56 pm

htg.

The pipe is coming from the wall, has the draincock at the bottom. This pipe then subsequently is connected to the radiator via the wheel sheild valve for the rad. Are you saying if i drain this for a period of time whilst the heating is on it will start coming out hot?

Secondly is it possible that the rad may just need re-balancing as I've also seen that on other sites? Or does it sound like a straight forward airlock?
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Postby htg engineer » Sun Jul 27, 2008 5:12 pm

You don't want to drain with the heating on, as the pump may draw more air into the system, if the system is hot if you drain from this point - you will get hot water eventually.

Balancing is when you turn other radiators down slightly so that the heat is evenly distributed - this is normally achieved by closing the lockshield valves a few turns so that they cannot be accidently turned on fully again. As you have said you have tried turning all but one of the radiators off fully, points to an airlock, if they don't heat when all other radiators turned off - they're not going to heat with them only turned down.

If all worked well before you started draining, flushng and adding cleanser. Then yes it's an airlock.

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Postby nav122 » Sat Aug 02, 2008 1:44 pm

"Well i've managed to get air out of one of the radiators that i was having trouble with, and now it works fine. However - with all the other rads in the house closed apart from the final troublesome one downstairs - the pump seems to be pushing hot water back up the central heating feed rather than the expansion pipe. As soon as the pump is turned off, you can hear bubbling as cold water from the F&E tank then flows back down again.

To me, this seems to indicate a block in the system, but when i open the drain cock for the problematic radiator...it flows out hot. As soon as the heating is turned on, the pipe seems to cool instantly as though the pump is actually pulling water out from it?!"
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