Testing a central heating pump

Most pumps seem to come with dire warnings about not running them dry.

Anyone know why this is? Does a pump rely on water to cool it - albeit using 'coolant' at 80-odd degrees? Or is water needed to lubricate the bearing in some way?

It would sometimes be useful to test a pump dry - by running it for a minute or so -before fitting it, and I'm trying to assess the consequences of so doing.

Reply to
Set Square
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AFAIK it's mostly the lubrication of the bearing(s). Way back before I understood things I fitted a pump but didn't bleed it. It failed within 18 months, maybe less than a year. The replacement I bled (RTFM...) and that one hadn't failed when I sold the place a few years latter.

TBH I can't see much advantage to testing before installation. After all you'll have just fitted it so the isolation valves will work and the flanges won't have welded themselves to the pump, bit messy with the water in the pump but that is all.

Reply to
Dave Liquorice

The cast iron rotor on our c/h pump is definitely water-lubricated.

Run dry it *will* score in just a few seconds. Since I was mending our our pump it was apart, and I was able to use a drop of 3 in 1 on the bearing surfaces. Ran up ok without any complaints.

Reply to
Tony Williams

If you want to be safe you could dunk the wet end in a bowl while you test it. In fact as long as you've wetted the bearing it should be OK to run for a minute or so. I can think of at least one CH pump that's been run dry to the extent of telling anyone in earshot about it, and is still running OK now.

Reply to
John Stumbles

The water lubricates the bearings.

You should fit them with shutoff vaules on eiter side, in some sort of accessible place, so if they fail, you don't have to rip the house apart to fix em.

Rick

Reply to
Rick

I've had the shutoff valves fail (twice) more often than the pump (never).

Reply to
Andrew Gabriel

Thanks to everyone who replied. The general consensus seems to be that it is a *bad* thing to run it dry - so I shall desist.

[One reason for wanting to test it dry is that I'm experimenting with a delay timer - to keep the pump running for a bit longer than the boiler's pump over-run logic (if you can call it that!) does it for. Specifically, I want I keep it running during the period after the boiler stops firing but before the over-run stat decides that it's getting a bit hot, and it had better start the pump again. The timer is designed for an extractor fan - but is supposed to work with loads between 25 watts and 200 watts - so I see no reason why it shouldn't work with a pump - unless anyone knows differently?!]
Reply to
Set Square

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