Central Heating pump running SLOW ?

Hi,

Two visits from the maint company, first guy says boiler is noisy as the pump is running slow. Switching it to the two slower speeds makes the boiler noise go from a loud groaning to violent banging.

Second guy says that the pump is "electro mechanical" and can't run slow as its a fixed speed and that its sludge in the system.

Quite prepared to believe either but its not getting my system fixed.

Do pumps run at a fixed (but faster or slower speed depending on the switch setting) speed?

Also shaft or pump isn't horizontal, brochure with it says it should be. Is this a problem?

The shaft should be horizontal. ALWAYS !

The pumps technically run run at at a syncronous speed but because of the design there is considerable "slip" and in use they run at about 70-80% of the full speed.

The pumps can develop a fault, usually partial failure of the capacitor, whereby they run much slower.

I dont understand your use of the term "maintenance company". If there is an organisation responsible for your heating maintenance then why did they not change the pump or do whatever is necessary to sort it out?

Tony

Thanks!

I have a 5 star contract, (= insurance) so I can either get things fixed and claim, OR call them. They have now split their support between "boiler" and the rest of the system.

This resulted in the guy who normally does everything, coming and saying the pump is slow, found with two methods

A. Screwdriver against the case and handle against ear, change speed and noise decreases. B. turn speed down and listen to the boiler try and wrench itself off the wall.

However as this first guy can now only repair "boiler" problems then he called for another guy via the "help" desk.

No call back as expected, after a week waiting I call them, then person B comes, a plumber. He then says the pump is a electro mechanical or maybe electro magnetic, I can remember which and "it can't run slow" hence my original question.

The reason quoted for the slow pump that isn't was that the system had sludge in it but as he didn't have his water testing kit then he could not check for this. But "I" (me that is) could easily flush the system but "not using that stuff" the Fernox stuff I had bought recently.

Apologies for the rant, just waiting for the call from this national company (not british gas) to arrange the third visit.

Ah and forgot the 3 way valve is leaking and that isn't fixed yet.

The system has always had the recommended Fernox stuff in, maybe not changed every year but topped up now and again (how to check is the concentration is ok?) and when I just drained the system it runs clear, i.e. before adding the cleaner stuff. Does this sound like a system with sludge, also all the radiatoprs get hot quite quickly if i turn off the hot water so see to me that the pump is slow.

Regards

6666


I'm now waiting for the third visit

That demonstrates to me that a heating engineer is required to diagnose faults and that many plumbers are better off sticking to plumbing.

The plumber should have just changed the pump!

Any experienced heating engineer will know that pumps CAN run slow, mostly in my experience due to a faulty capacitor.

Pumps can also "pump less" due to dirt blocking the impeller.

Since the pump impeller can seize up then surely that is the best example of a pump "running slow" ?

I am not impressed by the response speed of your insurers. Why dont you tell us their name?

Tony

Can pumps run down? I have never heard of this or seen it? usually when the capacitor dies it usually just doesnt give the pump the jolt it needs to get going? And I am an experiance heating engineer.

Well this is a new one on me tony how do you check this?

6666 fernox do a wonderful piece of kit that will check the concentration of the inhibitor in the system, maybe this is what the second chap is talking about?

as for flushing out yourself, well I would not untill you know if its definately a sludge problem, what fernox stuff do you have? and did he say why you cant use it?

I am surprised you have not knowingly encountered this yet.

The simple test is to take it out and run it and see if you can stop it with a finger on the face.

A small finger will not stop it but an index finger will. Using normal force that is, not a heavy handed plumbers force.

You should try a few to get the feel of how much torque they should give.

Its an interesting fault on a combi. It gives the appearance of a blocked sec HE. I have most often encountered it on the 7-10 y.o. Aristons with Samulson pumps. In most cases changing the capacitor fixed it as those earlier pumps are not head interchangeable.

It rarely affects Grunfoss but more often Samulson and Myson pumps.

You will waste a lot of time if you cannot recognise it. If you were ChrisR you would have a stroboscope thing to measure the rotational speed but he can never find it when its needed so he is not any better off.

Tony

Thanks Tony

Maybe I have just be lucky, who knows but its a bloody good one to know. as for the Stetshscope dont think wont fit in me new case.

But I will keep an eye out for this but usually when the pump has gone it has just gone

I can see that it would put the cat amongst the pigeons in a combi with a plate to plate he but it would have show itself up when you mistaking replace the thing

Oh Well Live and learn

I love this site, its a bloody education

6666, when you get the heating co. out to fix the leaking valve ask them to replace the pump at the same time as it will save them another call-out. You might want to buy a pump just in case they "forget" to bring one or turn up with a Chinese made one. (Buy a Grundfos, the higher quality is worth the extra couple of pounds (about £50 from DIY shed)). It's money well spent if you have to take 1/2 a day off work for every visit, and if they come good DIY shed will happily take it back.

Take the old pump to pieces and look at the impellor, if it's waterways are full of hard gunge you have as good as confirmed a dirty system in which case take further action to clean it and stop new pump going the same way.

From your description though, you have a substantially clean system, ask the fitter to fill a jam jar with some of the heating water (when he fixes valve/changes pump) and let it settle. There should only be the slightest sign of sediment at the bottom after an hour. If you're still concerned buy a Fernox analysis kit from a heating merchant (about £25), follow the instructions to send them a sample of heating water and tap water, wait for their results and recommendations.
And you shouldn't drain and replace Fernox inhibitor every year, or ever!.

Could this happen to the pump and cause the temp differential across the plate to plate to be less than it should be causing the boiler to over heat ? but still be capable of heating the rads fine ??

I had this a few weeks ago and was adv by manufacturers to replace the plate to plate heat exchanger as there wasnt quite a 15-20*C difference across it and was causing the boiler to over heat, they sed it be a blockage in the heatexhanger.

I think in my case this did fix it as I dont belive the job came back in, but it be good to know if this pump could show these same symptoms?

meldrew's_mate said:

6666, when you get the heating co. out to fix the leaking valve ask them to replace the pump at the same time as it will save them another call-out. You might want to buy a pump just in case they "forget" to bring one or turn up with a Chinese made one. (Buy a Grundfos, the higher quality is worth the extra couple of pounds (about £50 from DIY shed)). It's money well spent if you have to take 1/2 a day off work for every visit, and if they come good DIY shed will happily take it back.

Take the old pump to pieces and look at the impellor, if it's waterways are full of hard gunge you have as good as confirmed a dirty system in which case take further action to clean it and stop new pump going the same way.

From your description though, you have a substantially clean system, ask the fitter to fill a jam jar with some of the heating water (when he fixes valve/changes pump) and let it settle. There should only be the slightest sign of sediment at the bottom after an hour. If you're still concerned buy a Fernox analysis kit from a heating merchant (about £25), follow the instructions to send them a sample of heating water and tap water, wait for their results and recommendations.
And you shouldn't drain and replace Fernox inhibitor every year, or ever!.

Click to expand...

i agree with draining and replacing inhibiter, but i would advise, on an open vented system, adding inhibiter to the feed and expansion tank yearly

Well, guys I bought an old chronometric rpm calculator off eBay, a while ago just for checking pumps and other rotating things Set it- press it agin` the shaft and it runs for a minute and tells you the revsPS would go with corgiman on the yearly top up.........get 20 years out of a pump then but 2 be fair it was only running the C/H ..water was on gravity

The official rule of thumb is to add inhibitor at the start and then add 1/3 amount of the SAME make inhibitor every year if there have been no leaks or rad changes etc.

Every ten years change the water and start again.

I was once called by an old fellow with an open vented system who wanted me to drain it and refill with inhibitor. I checked it and decided it did NOT need draining. I advised him to add the inhibitor ( as above ) and left making no charge.

Did another job yesterday for a young Chinese couple, only took about five minutes to get their boiler working again, again no charge!! I like doing those jobs! They then feel safe calling me again!

Tony Glazier

If you were ChrisR you would have a stroboscope thing to measure the rotational speed

Click to expand...

Actually mechanical contact is better because nondismantling proctological diagnosis can be carried out.

but he can never find it when its needed

Click to expand...

So he's got 2. Same reason he's got 3 digi manometers.

Also get yourself a multimeter which measures capacitance, you only need a few microfarads and many of the cheap ones will do that.

There's also something funny which happens to pump valves which makes them block up, so if swapping the head of a pump have a poke at the one you can reach . Any suspicions and the pump body has to come out.

ANd as hasn't been mentioned unless I'm not concentrating, pump impellers can come loose.

Did the same as Agile.......people felt safe and I got repeat business........but never got rich .....never could get the charges quite right ..........just waiting to use my mechanical contact rev. counter

"""proctologocal""" ???

My spell checker does not even suggest anything and google has never heard of it.

What's it mean Chris?

I do really love doing small jobs for free, it restores people confidence!

But its mainly for lower paid people and pensioners etc. Some of the older ones get a little upset because they are so honest and expect to pay for any service.

Where can I get two rotometers Chris?

Tony