Possible pump failure....or not?

[zigg]

Hi guys, finally got round to posting.
I have a long term central heating problem. We moved here about 11 yrs ago, and all was ok for a few years. (It looks like a DIY heating system) Then problems started to raise their heads....noisy vibrating pump, radiators not getting very hot etc. So after a lot of headscratching and asking around, I changed the pump.(the water was black!) Old pump was a four speed, new one is three speed, (Grunfoss).
All was ok for about 18 months after that, then the same thing began to happen. So I bought a new pump, this time a DAB, ( I couldn't believe only 12 month's warranty on a pump!) Again all was ok......for another 18 months or so, and now , here we go again. Radiators downstairs not getting hot for ages, and non getting anywhere near too hot to touch.
The water in the system is very clean looking. I put a cleaner in which seemed to slightly improve matters, but nothing like what it should be.
Could the pump have gone down again?
I checked the last pump I fitted, and, to be honest, there doesn't seem a lot wrong with it. There is no play in the shaft, either way, axially, or radially. All I can see is that the impeller is coated with what looks like a black graphity substance, which I understand is probably sludge.
But if there's sludge in the system, why is the water clear?
I have an engineering background, and a good grasp of the principles of the central heating system, but I'm no plumber. Any help would be greatly appreciated.
And if you want any more details, or have any questions, I'll be glad to answer anything.....thankyou.

 

[corgiman]

sludge sticks to the pieps and rads etc and is rarley that evident in the water, unless u have a TDS meter


sludge is a buuuger aint it

 

[Heyyouitsme]

after u replaced the pump was the rads getting hot ect as you would expect them too? if im not sure how sludge could be the problem (dnt flame me, im an engineer not a plumber - so just speaking theoretically) if there was sludge in the sytem would it not be seen at the pump when replaced, and also would there not be coldspots in the rads ect?

 

[zigg]

Corgiman, what's a TDS meter?
Heyyouitsme, yes the system worked ok when pump was replaced. I guess over time the reduction in efficiency was gradual so that I didn't notice until the second winter came around and the rads didn't get so hot. The pump works all summer in hot water mode.
I've been warned against using a strong sludge cleaner such as Fernox, because of the possibilty of creating leaks in an old system......is this sound advice, and if so what cleaner can I safely use?
Getting back to my first replacement pump, (the grunfoss) how can I tell if it is worn out ,or not, bearing in mind there is no play in the shaft, and it spins round under power in the vice in the shed. The first of 3 speeds doesn't work by the way, but that's an electrical problem, the other 2 speeds work fine.
All suggestions are greatfully received guys.

 

[JohnD]

Black water and pump troubles...


There is a device called a Magnaclean that traps black sediment from the water with a magnet, and can be emptied out. This will catch the circulating sediment that I think is clogging your pump. It will probably cost you about £100 plus fitting and last a long time. You can find a very entertaining demo video if you do a search. There are several other magnetic trap devices on the market now.

However I think you should also give it a chemical clean (to get out what you can of the existing sludge) and add inhibitor after rinsing (to prevent any more being created).

What is the reason why you were advised against flushing? Is it very old and rusty? I am just an ignorant householder, but some of the pro.s on here may be able to suggest different cleaning methods.

p.s. the reason you can't see much sludge in the water is that it is heavy, and likes to sit at the bottom of radiators or cling to the insides of pipes and pumps. A small proportion of it circulates round looking for somewhere to settle. If you take a rad off and hose it through in the garden you will probably get a lot out.

 

[zigg]

The reason I was given not to use anything 'nasty' like fernox, was because he reckoned that if any part of my system 'had worn a bit thin' then using such a vicious cleaner might cause a leak. My system isn't rusty, but it's probably oldish, don't ask me how old tho.
(That Magna clean device looks good, but £100 is something I can't afford just now......might have a go at making my own tho...)
I've turned the pump up to the 2nd speed which might have maginally improved things, or it could be my imagination, either way nothing drastic has happened.
I've also bled that pipe that runs up alongside the immersion tank, with the little knurled screwcap on it, and got a fair bit of air out of it, but again, nothing spectacular has gone on.
I do notice that, the feed pipe dropping into the kitchen is almost too hot to touch, but that the return is almost cold. Would I be right in thinking that the reason for this is that the cold water ,being heavier than the hot feed water , is proving too much for the pump to push back upstairs ?If that is the case, does that point more convincingly to a failing pump?
As I said in my other posts, I have run the pump that was replaced, and it seems to have plenty of grunt in it, how can I test if it is ok or not..........or can't I?
JohnD, as to your comment on sludge wanting to sit in the bottom of rads etc......when I came to replace the first pump, every radiator gave out water as black as ink then..........from the bleed valve.....
I'll add more info as and when I can think of anything that may help you guys to think of a solution to my woes.
Thanks again fellas

 

[ChrisR]

See mains flushing in the faq section. Free unless you have a water meter!

 

[zigg]

Ok, I'v decided it's the wrong time of the year to be draining down the system, and posibly making things worse that they are. So my plan of action is to put some sentinel X400 in and leave it there til the heating isn't needed ..............spring time. Then get stuck in and sort the problem out properly.Anyone think this is a bad idea?....Or even a good one?