Central heating pump bearing replacement

I have just placed an order for yet another replacement central heating circulating pump. The current unit fitted has failed in the same way as its predecessors - noisy operation due to bearing wear.

These units seem to last around 5 or 6 years and are neither that expensive (£50 delivered for the just ordered new low wattage pump) or too difficult to replace (isolating valves fitted), but it still grates to replace a unit that is electrically functional & "just" requires replacement of the plain (water lubricated) bearings to cure the noisy operation.

Has any one here tried to do this - either sucessfully or not ? If so, what did you use for the bearing material ? I have previously completely dismantled one of the earlier failed units, but didn't get any further than that. When the next one gets installed I will have 2 to play with, from different manufacturers.

Nigel B.

Not answering your question at all - sorry! - but if you don't have a filter in your system, get one, as the pumps would last a lot longer.

Rob

Have you checked the pump shaft is exactly level.

These pumps should last 'forever'..

I am amazed that your pumps fail so quickly. I have a Danfoss that lasted 40 years. Changed it when I did some work on the system, thinking it must be worn out. Not a bit of it, so I have a spare which I doubt I will ever need to use.

I do have a filter, but this never catches much particulate matter.

Andrew.

The builder of our house fitted cheapest available of most items. I replaced the first central heating pump like for like after a few years when it failed (partly seized, would not start reliably). The replacement went very noisy after a few more years (turned out impellor was loose on the shaft).

Being fed up I asked at a nearby heating spares supplier if they could recommend a higher quality pump. They did, it was quite a bit more expensive than the 'basic' brand. I installed it - immediately noticed it was MUCH quieter in operation, and I've now forgotten how many years ago it was purchased. No trouble since.

+1 for Danfoss. Our first central heating system installed in 1975 had a Danfoss pump and along with everything else in the system was still going strong when we moved in 2004, Current system in the newer property is a combi boiler so contains its own pump. Neither system has a used a filter of any kind.

Usually when a bearing fails on a central heating pump it’s because the pump has not been positioned correctly with the failed bearing at the highest point allowing trapped air to ruin the bearing seals which must be completely immersed.

Do you loosen off the big screw on the top of the unit till water dribbles out?

How black is the water? Too much black rust in the water and a low fitted pump don't mix well.

I had an original Danfos central heating pump which was at least 20 years old and as I was having a new condensing boiler fitted told the plumber to fit a new pump. The boiler had to have a magnetic filter fitted to have the 7 year warranty and thought that was that for a long time. The pump started vibrating and was noisy after about 6 months and on strip down it was found to have foreign material in the vains of the impeller. The original had a simple open impeller but the new super pump has a slot type impeller which has slots which taper as the slot gets thinner to the outlet. The impeller was partially blocked and out of ballance which made the pump vibrate. I tried to buy an old style pump but they were not available. It was also found that the original pipe work was firstly used by a coal fired back boiler, before my time, and the pipework was filled with solid like iron deposits like a coating. It took various descale and chemical cleaners over about 6 months to we think to rectify that problem and yet again another pump change as a seal was leaking.

David

Another idea to think about is dissimilar metals in your system - like additional radiators installed using plastic pipe causing electrolytic corrosion, Iron fittings etc.

Bob

+1 for a combined cyclone and magnetic filter. Having worked on a few systems in houses I have owned; installers clearly don't always correctly flush out and properly clean systems when they commission them. The various valves in the boiler of one such system were partially blocked up with lots of metal particles.

Inhibitor is also very important - most systems have several dissimilar metals; Copper, iron, aluminium, so a good quality inhibitor is a must

Pumps should ideally be installed in the colder return pipe for better longevity, rather in the much hotter boiler outflow pipe.

A pump that stalls and refuses to start can be caused by the motor capacitor going faulty, most likely due to excessive heat, as above. Capacitors can be replaced.

A decent quality pump, in a properly installed and commissioned system, will last for years and years.

Edited By John Doe 2 on 06/11/2022 23:32:30

This was the pipework just below the pump. The two pipes were the fill and expansion pipes and the elbow was about a foot below the pump. Apparently thus is the place where blockages happen if anywhere. The pipe was 22mm dia .

David.

My mum went through three pumps rather quickly, and it turned out she was fiddling with the controls to 'save money'. In particular she kept turning down the boiler temperature. In consequence, the pump had to run much longer to raise room temperatures because her radiators only contained relatively cool water, and a lot more water had to be pumped to get enough heat into the house. Her central heating pump was on almost continually.

Quite different from my equally Scrooge-like strategy, where the boiler temperature is kept high, and money saved by turning the room thermostat down and timing the system so the heating is only on twice a day for a couple of hours. I don't touch the heating controls unless it's very cold, weedy visitors are expected, or I'm unwell. My approach isn't for everyone! It depends very much on having a well insulated house with big south facing windows, and of course the occupant being moderately active.

Training is needed. Took a while, but I've become acclimatised to a lower temperature and - with jumpers - am comfortable at 18°C. When I was married the wife kept the house at 22° and 18° was downright chilly, but it's actually OK. Now I find hospitals and other homes uncomfortably hot.

Dave

Thanks for the comments so far.

The system layout is as originally installed when the house was thrown up by Beazer Homes in 1989- all copper pipes & steel radiators, though it is a 10mm microbore system. The original Ideal Elan boiler (cast iron heater exchanger IIRC) was replaced with a Remeha Advanta system boiler (stainless steel heat exchanger) some years ago. IIRC the original pump was a Grundfoss, the current is a DAB Evosta - a 3 phase pump with integral inverter rather than a traditional 3 speed type. Others along the way have included a Wilo & a "cheapest I could get from Ebay" - all have lasted around 5-6 years before becoming noisy & all appear to have performed equally until they failed.

The original unit did last the longest, but while investigating poor system performance with the original boiler I found the impeller almost completely blocked with rusty steel wool & copper shards from the original installation. Clearing this out imporved system performance no end, but the pump got noisy a few months later.

The last time I drained down, the water that came out looked about the colour of weak tea, with nothing much in the way of sediment. I live in a soft water area & use an inhibitor. The radiators get equally hot & don't require much in the way of bleeding - what "air" there is tends to accumulate in a towel rail radiator, which may require a quick bleed once per season when the top rail goes cool.

The pump is installed with the motor shaft horizontal & height-wise the pump is aound 1/3 of the way up the hot water cylinder. The system is vented & the header tank is around 2 metres above the pump. I do bleed the replacement pumps on installation. Boiler operating temp is 70 C & needs to be to warm the house with the radiators originally specified..

When I get the capability back (had an arthritis related hand operation a couple of weeks ago & it will be a few months before my right thumb works again) and the inclination, I'll delve deeper into the noisey pumps I have to see if they could be rescued.

Nigel B.

A lot of this "Feeling cold, turn up the central heating" is psychological. I was once flat broke and it was a cold winter. My goodness the house felt cold, with no heating. So I went outside for 20 minutes and got bitterly cold. Returning to the house, it felt delightfully warm!

Andrew.

I'm still hoping to read what bearing material as a matter of interest. Colin

We had a new boiler installed a few years back and they fitted a magnetic filter. Even with a power flush it still picked up quite a bit of debris when the system was first fired up. These days it’s only a tiny amount when the engineer cleans it. Over time I’m sure the particles wouldn’t do the pump much good if we didn’t have it?

""David George 1:

This was the pipework just below the pump. The two pipes were the fill and expansion pipes and the elbow was about a foot below the pump. Apparently thus is the place where blockages happen if anywhere.""

That is absolutely appalling, Dave. The "plumber" who did that, (or rather didn't - flush the system), should be shot !

I found a similar horror when I dismantled a combi boiler that wasn't working very well; valves half blocked up with swarf from "plumbers" who couldn't be bothered to do a proper job. Lazy sodding bastards - I bet they charged the full whack.

Fit a Fernox TF 1 "Total" magnetic cyclone filter while you have the system drained. Just under £100 from Screwfix and a good bit of kit. You won't be disappointed. Look at the guarantees with new boilers: 7-10 years if fitted with a filter, 5-7 years if not.

Like SoD, I set our heating to come on twice a day, and I leave it up to the house and hot water thermostats to decide whether to fire up the boiler or not. Our house thermostat is set between 13-15 degrees. It is a mindset - turn up the heating or put on a sweater.

Being forced semi-retired, and not being larks, we don't need to get up early anymore, so I have set the heating not to come on until 1000, by which time the house has usually warmed up anyway. No point wasting gas heating the house when we are still warm in bed !

Edited By John Doe 2 on 07/11/2022 16:58:49

Our original circulating pump lasted for over 40 years; with minor attention.

When it began to knock, it was stripped, form investigation. The bearings were OK m, but there was end float on the impeller. Inserting shims cured the end float, and the noise. After about along time the knock returned, the copper shims had worn, allowing the impeller to float to and fro as it passed the poles of the magnetic drive.

The most effective and long lived shims were plastic rather than metal ones.

Eventually, the bearing did wear radially and repair seemed very difficult, so, finally, it was replaced.

If this one lasts for 20 years, I am unlikely to worry about replacing it!,

Edited By Howard Lewis on 08/11/2022 04:19:37