hot water for central heating not circulating

puntaprimapete · 7 Mar 2008

Over the last few weeks we have been losing heat to the radiators. The one furthest from the boiler going first. I suspected it was being caused by sludge in the system causing a blockage especially as most of the downstairs radiators were very old and had microbore pipes. I installed brand new radiators and valves and replaced all the pipework with 15mm 'T'd off the 22mm flow and return. Still no joy. The pipes on the flow side would get hot after quite awhile but there was no heat on the return side. Even the return by the boiler remained cold despite the boiler firing up regularly.
I then called out an engineer from Heat Team who we have boiler breakdown cover with. He said the boiler and the pump were working fine and that the system had a blockage.
I have spent the whole day disconnecting every rad and with a rigged up hose pipefrom the outside tap have succesfully flushed every pipe back to the boiler connection. But still no good!.
I even tried shutting every rad in the house off bar one of the new ones
It did get hot eventually about 3 times longer than it used to take for all the rads to get piping hot, but the return pipe barely heated up at all and by the boiler it was still cold.
I can't see that it's possibe to have a blockage when I have confirmed that every pipe is running clear back to the boiler and if it's not the pump failing I am at a complete loss what to try next.
Any ideas or advise would be greatly appreciated.
My boiler is a baxi 105 HE

Softus · 8 Mar 2008

I don't understand how you ensured that water was flowing in the direction you wanted.

Your reasoning is that there can't be a blockage because your flushing activity would have encountered it.

My reasoning would be different - you appear to have a blockage, therefore your flushing didn't achieve what you think it did.

How have you tested that the pump is pumping?

puntaprimapete · 9 Mar 2008

I think part of the problem was an airlock. I managed to force some air out of the system and it seems to have restored the system a bit. I'm struggling to get all the radiators hot still but I think this might be a balancing problem. Do you have any good tips for doing this?

superdupergasman · 9 Mar 2008

flushing with water some times just does not clear it, or its just moved.

Is this an open vented system??

Try cutting out the cold feed connection into the system?

OR

If the cold feed used to connect into the flow/return at cylinder, and its be altered to a close proximity system, the return connection of the cylinder into the return from rads.

To clear airlock, crack fittings at rads and let the water flow out for a bit.

Softus · 9 Mar 2008

Have you tested that the pump is running?

If so, how?

puntaprimapete · 9 Mar 2008

This is a closed system (combi boiler) The pump appears ok when the heating turns on the needle on the pressure gauge flicks up really quick. Do you think adding a chemical cleaner might help restore the sustem?

Softus · 9 Mar 2008

puntaprimapete said:
The pump appears ok when the heating turns on the needle on the pressure gauge flicks up really quick.

Is that really the extent of your testing of the pump?

Do you think adding a chemical cleaner might help restore the sustem?

I think avoiding random guesses at the cause of the problem is the best course of action.

How do you know that the pump is running?

If you don't know, then why do you want to assume that it's running?

How do you know that there was an airlock?

If you don't know, then why do you want to assume that there was an airlock?

puntaprimapete · 9 Mar 2008

I haven't tested the pump at all this was done by the engineer who came out on thursday. He assured me the pump was fine and showed me the needle flicking up as confirmation.
Can the power of a pump fade as it gets older or is it simply a case of working or not working.
As for the airlock I didn't know I had one but I thought it was worth letting water flow out of a rad at the top of the house and it did clear some air which has made some improvement.
Cheers
Pete

Bamber gaspipe · 9 Mar 2008

puntaprimapete said:
This is a closed system (combi boiler) The pump appears ok when the heating turns on the needle on the pressure gauge flicks up really quick. Do you think adding a chemical cleaner might help restore the sustem?

Pump/ airlocked.

puntaprimapete · 9 Mar 2008

Ok I'll check it out. Thanks

Rob · 9 Mar 2008

I dont believe you replaced all your rads and pipework!!

But thats besides the point because if you cant even get the nearest rad working with all the others OFF then chances are theres a blockage in/near the boiler.

Personally id drain down remove the isolation vlaves and clean out. Also remove pump and housing and also give a rinse out. This is where its most susceptible to sludge on the heating side

Bamber gaspipe · 9 Mar 2008

rob884 said:
I dont believe you replaced all your rads and pipework!!

But thats besides the point because if you cant even get the nearest rad working with all the others OFF then chances are theres a blockage in/near the boiler.

Personally id drain down remove the isolation vlaves and clean out. Also remove pump and housing and also give a rinse out. This is where its most susceptible to sludge on the heating side

I still think it`s the pump.

Softus · 9 Mar 2008

rob884 said:
I dont believe you replaced all your rads and pipework!!

I concur. But if he/she did, then I don't believe that it would work afterwards.

All we have from the OP is misinformation. Oh, and a persistent inability to answer direct questions. Not to mention the unwillingness to follow a reasoned fault-finding process.

The Baker · 9 Mar 2008

Can you supply the Boiler Make Model and Gc no thats the gas council number.
This information may help the DIYNot Herbert's to solve your little brain teaser.

Tim

Softus · 9 Mar 2008

The Baker said:
Can you supply the Boiler Make Model and Gc no thats the gas council number.

Why do you think that information has any relevance (yet)?

diynot

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hot water for central heating not circulating

Bamber gaspipe

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