Alde Pump Clatters After Water Temperature Rises

[Dr8ton]

Thought I should share this in the hope that someone will kindly help me out...

 

I have an Alde 2920 "Comfort" boiler, fitted in 1994. I bought the boat in 2004 and the circulation pump (manually activated with an "on-off" slider on the thermostat) has run flawlessly and silently since. I believe it is the same pump used in all the original comfort boilers and has changed little (but don't quote me!). Anyway this little fellah has been happily doing his job pushing a mix of water and glycol around my CH system from inside his plastic expansion bottle. Until recently when he threw all his toys out....

 

It didn't whine, like a bust bearing or bush, but clattered. The clatter only became audible after 20 minutes or so with the Alde on "full bore". If you already know the answer then I'd love to hear from you. Otherwise, you can "bail" now or toil to the end of the post!

 

I removed the pump and took a long hard look at it. The shaft and spindle seemed straight and true but the notched lower washer was a little worn (compared to the similar sized cap washer) and stuck with crusty residue. I carefully cleaned it off.

 

Spinning the impellor by hand didn't reveal any "slap" so I clamping the thing in a bucket of cold water and wired the motor to an obliging boat battery. It ran smooth and quiet for a couple of hours - no problem at all, even after I "tortured" it with hotter and hotter water. This persuaded me there might be nothing wrong with the pump, mechanically or electrically, except of course the middle of a big bucket is not its natural habitat - so not the same load.

 

The next step was to banish any particles in the CH system that might have been getting stuck between the impellor blades and the surfaces of the impellor well (at the bottom of the expansion bottle). So with the help of a plumber, we introduced flush points and trickle-rinsed the entire system (using just domestic tap water) until it ran out perfectly clear. That done, we removed the expansion bottle from the Alde boiler so I could clean it out thoroughly, especially the well-end of it where the impellor sits, minutely scraping off vulcanised rubber (detritus from the lower washer) and other stuck "grot". We needed a variety of cunning tools for this job (owing to the awkward shape of the thing), including an old half round file and some emery paper wrapped around a "Henry" vacuum cleaner tube. But in the end we did manage to clean it up "as good as can be". After I refitted the pump inside it's bottle I continued my torture regime in the bucket. Everything looked and sounded good.

 

We then relocated the expansion bottle (with the pump already inside) and recharged the CH system using 50% Glycol. I reignited the boiler, switched in the pump and waited. As before, the pump ran perfectly for 20 minutes then "clatter-clatter" just before the boiler shut down (with the thermostat set at around 25 degrees C). The noise is like sticking your fingers between the spinning blades of a 12 volt miniature fan.

 

All I can think is that hot water causes the shaft, the spindle or the washers to move just enough so the impellor catches (to function efficiently there is not much space in the well for the impellor to spin). But the odd thing is that there is no warning. The pump goes from silent to constant clatter - not a gentle transition as the temperature rises. Instead there seems to be a precise critical temperature that triggers the problem. It then goes away when the water cools just enough.

 

Finally, and for what it is worth, I did discover that unscrewing the cap a turn or two seemed to stop the clatter, albeit briefly. So we banged an extra "spacer" washer inside the cap to see what that would do (in case somehow the blades were scraping the bottom of the bottle) but it didn't make a jot of difference.

 

Unless I can begin to understand the problem I am reluctant to buy a new pump (they are expensive little blighters). But short of doing exactly that, I really don't know what else to try. I'm stumped, basically...

 

Any thoughts?

 

Thanks,

 

Dr8ton

 

PS I phoned Alde for a chat but am yet to hear back from their engineers.

 

[Stormbringer]

Long shot ... but maybe its the expansion bottle that is reacting to the temperature and not the pump ?

 

Good luck

Andy

[Jo_]

Graham Cutmore is the Alde engineer wizard. http://www.grahamcutmoreengineering.co.uk/

 

He looks after ours and lots of other boaters' systems.

 

You could give him a ring you could talk things through.

[Ray]

I'll be interested to hear the solution. Our pump does similar until we learned not to run the boiler at full tilt for any greta length of time. And our boiler's only just 5 years old.

 

BTW, Alde will also service their burner and appear to be about 50% cheaper than Graham even though Alde implied that Graham is the person that ctually does the servicing on their behalf!

[smileypete]

Spinning the impellor by hand didn't reveal any "slap" so I clamping the thing in a bucket of cold water and wired the motor to an obliging boat battery. It ran smooth and quiet for a couple of hours - no problem at all, even after I "tortured" it with hotter and hotter water. This persuaded me there might be nothing wrong with the pump, mechanically or electrically, except of course the middle of a big bucket is not its natural habitat - so not the same load.

Could be there's excessive 'end float' where there's axial play on the shaft.

 

Whether that makes for a noisy pump may depend on whether the pump is pushing or pulling due to restriction upstream or downstream of the pump.

 

If you can test this by adding some restriction upstream or downstream while testing or in situ it might make the noise disappear or reappear.

 

Or it just might be air getting trapped in the impeller, in this case turning the boiler off for a few seconds and back on may allow it to bleed off somewhere else.

 

cheers, Pete.

~smpt~

Edited June 10, 2013 by smileypete

[Dr8ton]

Many thanks for all the input. It's very much appreciated.

 

I managed to get hold of an Alde engineer today. The top washer on the circulation pump (the one the expansion bottle cap tightens on to) is made out of EPDM. These washers commonly sag with age. When that happens the pump drops a little so the gap between the impellor and the bottom of the well that it sits in becomes compromised. Then, when the washer is thin enough due to age, hotter water further increases its tendency to sag.

 

Solution?

Reverse the washer!

 

I am back on the boat this Friday and I'll give it a go. Immediately afterwards I am away, so I'll let you know how I got on when I return to the UK in July.

 

Apparently, for those wondering, the best place to buy the washer (in case one turns out to be needed) is Midland Chandlers.

 

Jo_: At some point I will need to do a gas appliance test.There are a few Alde approved service engineers who do boat work in my area (the East of England). Graham Cutmore of "Graham Cutmore Engineering" is one. The Alde engineer I spoke to described him as a "top man".

 

Ray: I believe all the Alde approved engineers are independent and their costs vary. As you will know, Graham is based in Northamptonshire but covers the country. I am speculating of course, but If Graham travels further than the local engineer and adds a supplementary mileage fee then his bill will be bigger, no?

[Ray]

Alde quoted me £45 for a burner service (plus parts). Graham quoted £85 for similar. Ironically, from what I could make out, Graham actually does the Alde services for them.

 

I shall take a closer look at the washer and try reversing it when next at the boat.

Edited June 10, 2013 by Ray

[Dr8ton]

Forgot about this post:

 

Reversing the washer did not resolve the problem so I fitted a new pump.

The washer idea might work for others though...

 

Dr8ton