Any plumbers? Why do CH pumps fail?

norm

norm

norm

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I've got a Glowworm 24CI boiler than was intermittently tripping out with overheat codes (F14,F5).

I could feel the pump wasn't turning on before this would happen. Either the pump was failing or the control board wasn't supplying the necessary power to the pump.

Today I've replaced the pump with a refurbished one and it sounds noticeably more powerful and hasn't had any issues so far.

Taking a look at the old pump https://imgur.com/a/LyVJkqf

Why might it have failed? It spins freely at the impeller and doesn't have any debris in it. There's a big capacitor on top of the pump could it be that?
 
ci_newman said:
Most likely the brushes inside the motor have worn / burnt out. They are a moving / mechnical part, eventually they will wear out.
Click to expand...

Are the brushes connected to the impeller and that all sits and spins inside the metal body pictured? I assume it's removable so you could easily swap it out, although I've only really seen full replacement pumps for sale though?

DncurfM.jpeg
 
I've had a CH pump fail recently too and I replaced it with a cheap BritTherm pump, definitely a lesser copy of the Grundfos one I removed (below). It's noticeably noisier, sends vibrations along the pipes and was a pain to bleed.

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I'm not a plumber but I can think of a few reasons why they fail -

- cavitation - if there's a sufficient enough air pocket in the pump it will just spin and not move any water, then overheat and seize or damage it electrically (there aren't usually any brushes in a CH pump).
- the capacitor fails which mean the pump can't start (the capacitors only function)
- foreign debris gets lodged in the pump and jams the impeller - it's constantly powered so over heats and fails as before.
- if a zone valve fails internally (doesn't open but still gives a closed signal) and the radiator bypass valve of your radiators is poorly balanced then the pump is pumping against a blockage and overheats and fails as before. This is what happened to me, see the image above.

That's a few from the top of my head but I'd say the most likely causes are foreign debris getting loose and jamming it or running it too long when cavitated - it's why a magnetic filter should be fitted and you should bleed your system often.
 
Mysterae_ said:
That's a few from the top of my head but I'd say the most likely causes are foreign debris getting loose and jamming it or running it too long when cavitated - it's why a magnetic filter should be fitted and you should bleed your system often.
Click to expand...

I fitted a magnaclean to try and protect the boiler a few years back, the water in the CH is very clean.

I think in my particular instance the automatic air vent that sits above the pump was found to be not working as it was caked in limescale blocking the vent port. So after I drained the system down to work on the radiators one time the boiler wouldn't run correctly afterwards as I suspect air was being trapped in the pump like you state, whether that partially damaged the pump I'm not sure. Once the pump was running though it was fine it was just starting that was the issue.

So maybe the capacitor that sits above is faulty, not something I can test with a multimeter?
 
norm said:
I fitted a magnaclean to try and protect the boiler a few years back, the water in the CH is very clean.

I think in my particular instance the automatic air vent that sits above the pump was found to be not working as it was caked in limescale blocking the vent port. So after I drained the system down to work on the radiators one time the boiler wouldn't run correctly afterwards as I suspect air was being trapped in the pump like you state, whether that partially damaged the pump I'm not sure. Once the pump was running though it was fine it was just starting that was the issue.

So maybe the capacitor that sits above is faulty, not something I can test with a multimeter?
Click to expand...

Some magnetic filters also capture the debris that isn't magnetic (flux, PTFE bits) in their trap but the cheaper filters don't have this, I'm sure the Magnaclean ones do.

I presume you bled the pump well, the big screw on the front of the pump? Like I said the BritTherm pump I fitted was a pain to bleed and wish I'd fitted a newer Grundfos pump that self-bleeds (UPS3).

You can test the capacitor - plenty of vids on youtube but be careful as the cap may contain a charge!
 
norm said:
Are the brushes connected to the impeller and that all sits and spins inside the metal body pictured? I assume it's removable so you could easily swap it out, although I've only really seen full replacement pumps for sale though?

DncurfM.jpeg
Click to expand...
Nope, the brushes are normally static blocks of carbon (spring loaded to put pressure on the commutator ring), and they wear out, and suddenly you don't get electrical connectivity between the power supply and the windings any more, and the pump stops.
 
Sinbad2000 said:
Nope, the brushes are normally static blocks of carbon (spring loaded to put pressure on the commutator ring), and they wear out, and suddenly you don't get electrical connectivity between the power supply and the windings any more, and the pump stops.
Click to expand...
I'm well confused - are you talking about heating pumps or motors in general?

I thought it was quite obvious from photos that the pumps above (and D5/DDC pumps in computers) are brushless and work by having multiple coils energised in sequence. Then magnets on the impeller shaft. Am I missing something?
 
LuckyBenski said:
I'm well confused - are you talking about heating pumps or motors in general?

I thought it was quite obvious from photos that the pumps above (and D5/DDC pumps in computers) are brushless and work by having multiple coils energised in sequence. Then magnets on the impeller shaft. Am I missing something?
Click to expand...

This I don't get either. If the magnets are on the impeller shaft, how does the metal body they sit within not interfere with the magnetic field.

I'll most likely try and take that bit apart having spoken to the company who sold the refurbished pump and explained the symptoms they suspect the old pump overheated and possibly damaged one or more of the coils.
 
norm said:
This I don't get either. If the magnets are on the impeller shaft, how does the metal body they sit within not interfere with the magnetic field.

I'll most likely try and take that bit apart having spoken to the company who sold the refurbished pump and explained the symptoms they suspect the old pump overheated and possibly damaged one or more of the coils.
Click to expand...
It'll probably depend on if the metal body is magnetic, or a non magnetic one (possibly an aluminium alloy or something similar).
 
If you flush a rad that's been working for years you'll see one reason why and that's the accumulated build up of rust and scale. So I'd put money on the pump innards getting scaled up and then the motor runs hotter plus the heat from maybe being in a sealed environment with a heat source kills the electronics.

I replaced my Grundfos pump myself and flushed the CH system at the same time so the cost of a another Grundfos pump was insignificant. Rads also had to be changed as the previous owners didn't do any maintenance so the rads were basically rusting from the inside.
 
LuckyBenski said:
I'm well confused - are you talking about heating pumps or motors in general?

I thought it was quite obvious from photos that the pumps above (and D5/DDC pumps in computers) are brushless and work by having multiple coils energised in sequence. Then magnets on the impeller shaft. Am I missing something?
Click to expand...
Brushed motors in general. I am unable to see the photos while at work, as image hosting sites are blocked. Sorry if I was on the wrong track.
 
You can test if the capacitor has failed (Without a microfarad tester). Plug the pump in with the volute / housing disconnected - If the pumps hums but fails to start give the impeller a flick with a screwdriver and if it runs you have a faulty capacitor. If you have a microfarad tester - disconnect the capacitor and then test with a lead on each wire / spade - check the reading to the recommend range on the capacitor.
 
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