Heating no circulation

A mostly old Y plan system.... Symptoms of dwindling circulation occurred, lower rads not heating, upstair s output tailing off then the system quit entirely. Boiler said dry fire er ror, it was filled but presumably no circulation. Filter has been emptied o f muck, pump has been opened & is clear. What else is likely to have failed the circlation? The 3 way valve isn't blocking rad flow in HW only mode, b ut getting the bottom part of it off the pipework to fit a new ball looks l ike a right mare of a job. Access is terrible & the pipework around it allo ws it no movement afaics. I don't see that causing the problem. Clues welcome, right now I lack one!
NT
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On 27/03/2019 20:31, snipped-for-privacy@gmail.com wrote:

What's "dry fire error"?
What's the rate of flow on the HW side? How hot does it get?
Does the HW get hot when just CH is demanded?
Can you hear air/cavitation when the pump is running?
I think there is a lot of analysis still to do.
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On Wednesday, 27 March 2019 20:47:16 UTC, Fredxx wrote:

boiler thinks it fired with no water, ie temp shot up fast

there's no primary circuit flow. It's not a combi

there's no primary circuit flow. It's not a combi, so HW cyl was cold until immersion used.

will check tomorrow.

Surely. I just was left very puzzled today when I found the pump not blocked.
NT
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On 28/03/2019 00:42, snipped-for-privacy@gmail.com wrote:

I meant on the HW primary circuit.

So no circulation at all, including HW cylinder primary. Earlier you said, "The 3 way valve isn't blocking rad flow in HW only mode" implying there was flow here?

Any evidence it turns? Perhaps a cap gone bad.
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Also one can feel the pipe and see how far the heated water gets.
Sounds like sludge. I hate CH. Brian
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On Thursday, 28 March 2019 09:46:25 UTC, Brian Gaff wrote:

less than a foot from the boiler.
NT
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On 27/03/2019 20:31, snipped-for-privacy@gmail.com wrote:

Are you sure the system is correctly filled with water and there are no airlocks?
I've seen the symptoms you describe once (without the electronic warnings), on a neighbours system which was all but empty- the gate valve from the header tank was closed. When I opened it and bled the radiators, all was well.
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On Thursday, 28 March 2019 10:00:38 UTC, Brian Reay wrote:

tairs output tailing off then the system quit entirely. Boiler said dry fir e error, it was filled but presumably no circulation. Filter has been empti ed of muck, pump has been opened & is clear. What else is likely to have fa iled the circlation? The 3 way valve isn't blocking rad flow in HW only mod e, but getting the bottom part of it off the pipework to fit a new ball loo ks like a right mare of a job. Access is terrible & the pipework around it allows it no movement afaics. I don't see that causing the problem.

I drained it, a lot came out. Not sure what else I can say. I'll check out the pump some more today.
NT
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On 27/03/2019 20:31, snipped-for-privacy@gmail.com wrote:

Blockage or airlock sounds the most likely. You could start with a drain down and refill. If that does not help, then a mains water flush (temporarily block the vent and F&E pipes).
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John.
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On Thursday, 28 March 2019 10:35:51 UTC, John Rumm wrote:

nod

puzzled by that bit though
NT
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On 28/03/2019 10:45, snipped-for-privacy@gmail.com wrote:

If you are (for example) injecting mains water into a disconnected rad tail, and draining from the other, you want all the flow to go through the pipework and rads, not to be forced into the F&E tank where it might overwhelm the overflow.
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On Thursday, 28 March 2019 13:18:15 UTC, John Rumm wrote:

in

Ah, got ya.
Update: Today I set the room stat to minimum so the boiler didn't fire & switched t he system on. Previously I found the pump wasn't getting power from the boi ler, so temporarily rewired its live to permanent live so it runs all the t ime, which would at least get the thing running. So the pump's been on. It' s definitely spinning, I can hear that clearly & can hear bubble or cavitat ion type noises.
However... the primary circuit & downstairs rads are all cold, despite runn ing through the HW cylinder that's hot from the immersion. So I can only co nclude that primary circuit water is not flowing thru the HW cyl heat excha nger. Why I don't know.
The system was drained & refilled the other day. The plastic header tank co nnected by copper pipes contains a LOT of rust pieces & dust. The system is nearly 40 years old and I don't know whether there has been an increase in recent times in rust deposition. A magnetic filter was fitted 2 years ago.
Oh, when it first went wrong I discovered the header tank overtaken with bi ofouling. That has gone without a trace now, the chemicals wiped it out.
So something somewhere has to be blocked. I guess the first moves to make a re to blast what I can with mains water & to add cleaning chemical. However this system had all the rads flushed out 2 years ago & has been cleaner ch emicalled a few times... it plainly hasn't solved it. I'm beginning to thin k the only solution is to take all the plumbing apart & blast every bit out . I hate the thought of doing that though.
PS one downstairs drain points drains freely, the other barely manages to d ribble.
NT
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On 28/03/2019 19:52, snipped-for-privacy@gmail.com wrote:

Just to be on the safe side, you might check that the pump is actually pumping. That would be one thing checked off. If you could swap in a known-working pump from somewhere else, or plumb this one into a test circuit?
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On Thursday, 28 March 2019 22:08:14 UTC, GB wrote:

ed the system on. Previously I found the pump wasn't getting power from the boiler, so temporarily rewired its live to permanent live so it runs all t he time, which would at least get the thing running. So the pump's been on. It's definitely spinning, I can hear that clearly & can hear bubble or cav itation type noises.

I'm not sure how. But I'm also not sure how it would fail to pump given tha t it's making all the right noises, fizzy ones as well as spinny ones. I ch ecked its ports were clear.
NT
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On 28/03/2019 22:08, GB wrote:

Those were my thoughts, but NT was initially giving mixed signals of whether there was flow into the HW cylinder primary, or not.
I think its time to take off the pump and see if it run. If it has a screw on the end of the rotor on its removal it should be possible to see it turn under power.
Of course all the vanes could be missing, which is likely given the tales of gunk in a very old system. I've seen an old BMC water pump otherwise working ok, missing its vanes, causing the engine to overheat.
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On Thursday, 28 March 2019 22:48:53 UTC, Fredxx wrote:

n a

no there's certainly no flow there. If there were it'd extract DHW cylinder heat & send it to the rads at low level.

I know it turns. The noises indicate it does, it doesn't just hum.

This pump is 2 years old, has a plastic rotor with narrow water passages & the rotor is pristine & there's no blockage or debris there. The rotor turn s without problem. I really don't believe it's the pump.
I plan to mains water blast the drain point that only dribbles. It might be worth taking that rad outside to flush it, it's not been there very long b ut if there's no flow I guess that rad is the prime place debris would coll ect.
I must fit a valve to the header tank, mucking with it in the loft is a pit a.
NT
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On 28/03/2019 23:22, snipped-for-privacy@gmail.com wrote:

Then, it's a blockage in the system. Hopefully, mains pressure will clear that, but otherwise you have a bit of a job.
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On Thursday, 28 March 2019 23:33:17 UTC, GB wrote:

s & the rotor is pristine & there's no blockage or debris there. The rotor turns without problem. I really don't believe it's the pump.

Another update. There is certainly primary flow. It can be heard loud & cle ar from the filter. That means there's air in there, which is odd since fro m the filter it flows through the boiler then through a pot with F&E pipes out the top, and it's been running much of the day. But it's running.
The boiler is still displaying F72 fault code, NTC sensors out of range, th ough they've been replaced. It won't fire up. So it's looking like a PCB pr oblem and a blocked HW cyl heat exchanger. Sounds expensive :/
NT
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On 28/03/2019 23:22, snipped-for-privacy@gmail.com wrote:

We have just changed a pump. Though it would spin much of the time, it appears there was a 'flat spot' on it from which, if it came to rest on that, it could not restart.
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On 28/03/2019 22:48, Fredxx wrote:

My VW Passat started to overheat whenever the car went up a hill. When I eventually took the car to pieces I found that the plastic impellor had completely disintegrated. I was pleased with the replacement as that had a metal impellor.
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