How to determine a faulty pump

haf · 24 Jan 2006

Hi,
I have a CH problem thats been mentioned a few times before i.e upstairs rads OK-ish, downstairs cold. My setup is old backboiler with cylinder and pump/3port valve upstairs. Pretty much all the pipes around the pump and cylinder get very hot very quickly and the upstairs rads heat up in sequential order from pump with one closest to pump being the hottest and 4th in line being warm. No sign of any heat downstairs. I have done loads of research and testing and can pretty much exclude airlocks, bleeding (rads and pump) , balancing, sludge block, blocked feed etc. having searched this forum I suspect my problem is the pump and that the upstairs rads get hot via gravity but i can defintaly hear the pump spinning at different rates depending on speed. So my questions is how can i confirm its the pump? I saw one suggestion which suggesting dismantling pump by taking off using alan keys and then switching it on to see if it spins. Another suggestion was to stick a drilll/screwdriver bit through the front (not sure i understood this) I plan to have a stab at replacing the pump at the weekend but would welocme any other advice. B&Q have a selection of pumps so is there anything i should look for to make sure its ok for my needs? Thanks

Nestor_Kelebay · 25 Jan 2006

I have heard of circ pump impellers getting worn out, but the only explanation I can think of for that would be cavitation causing the deterioration of the impeller.

I'd try changing the impeller.

You say you've checked out balancing, and that's not the problem. What happens when you pinch off flow through the presumably longer upstairs loop? Do you still not get any flow through the downstairs loop? A closed balancing valve seems to be the most obvious explanation for no heat on a short loop and good heat on a long loop.

But, I have heard of "worn out impellers", too, infrequent though they may be.

ChrisR · 25 Jan 2006

SOunds like you've read the advice but not done anything. Pumps, impellers, pump valves all block. Take it apart.

haf · 25 Jan 2006

Thanks for your comments. I plan to take the pump apart this weekend as I only came to the conclusion that its most likely the pump at fault after reading these forums and eliminating most other things. I wasn't aware you could change bits inside the pump eg impellers. Are these 'standard' parts i can get from B&Q. To be honest I'd happily buy a new pump if that will solve my problem rather than attempt to fix the current pump. However I will strip pump down and see what i can find..
I did try closing all upstairs rads but that didn't make any difference to downstairs - i have 4 rads upstairs and 5 downstairs and my piping is microbore

Softus · 25 Jan 2006

haf said:
Thanks for your comments. I plan to take the pump apart this weekend as I only came to the conclusion that its most likely the pump at fault after reading these forums and eliminating most other things. I wasn't aware you could change bits inside the pump eg impellers. Are these 'standard' parts i can get from B&Q. To be honest I'd happily buy a new pump if that will solve my problem rather than attempt to fix the current pump. However I will strip pump down and see what i can find..
I did try closing all upstairs rads but that didn't make any difference to downstairs - i have 4 rads upstairs and 5 downstairs and my piping is microbore

It never makes economic sense for a tradesman to attempt to repair a pump, because they'd charge the equivalent of a new pump for just the labour!

So you won't get much advice on repairing. Anyway, the guy who advocated impeller replacement isn't in the UK.

If you've tracked down the problem to the pump, then just buy a new one. If you get the same make/model then you'll probably not have to modify any pipework or fit extension pieces. However, you'll pay far too much at B&Q - just go to a plumbers' merchant (where any local plumber would go). And if they're rude to you, then go to a different one.

Also, if you have any heating at all at the moment, wait until the cold snap is over before you start the job!

kevplumb · 25 Jan 2006

i can defintaly hear the pump spinning at different rates depending on speed.

that does not mean the impeller is i have known them come loose

haf · 29 Jan 2006

So much for my analysis of the problem. I took apart the pump and it looked fine. I replaced it anyway but my problem still remains. The only time my CH works is if I completely drain and refill the system. These seems to get my upstairs rad on but once the system switches off then it doesn't come on again until next drain.. major pain in this weather. The whole system is over 20 years old so am thinking of a complete end-to-end replacement. One plumber suggested a power-flush but I'm not convinced as system seems to drain and fillup OK... Getting an alternative quote tomorrow after BG said £5000.

ChrisR · 29 Jan 2006

10:1 your problem will be accumulation of sludge.

Have you turned off all rads except one, etc...?

Take a small "bad" rad outside and invert with water in continually for 10 minutes, and shoot the garden hose through, and see how much better it is.
Check your rad valves are opening and closing throughout the house.
Check you don't have a "soggy ball" in any zone valve.

haf · 1 Feb 2006

the plot thickens.. I now have no heat anywhere in the system - the boiler fires up for about 30 seconds and then stops for many hours. I had the boiler checked out by BG and they said it was OK and advised a powerflush at £600 which I'd rather not do as I'm getting the whole system repalced shortly. Any suggestions on doing my own power flush as a short term fix eg stick a garden hose in the feeder tank and force water through? As an asde i opened the screw in front of pump and the water barely dribbled out at setiing 1, at 2 and 3 the water didn't come out at all. So my feeling is that there must be some kind of lockage between boiler and pump but as its impossible to get to the pipes (behind walls and udner concrete floor) i'm not sure i can do anything to confirm this theory....

GaryMcGowan · 1 Feb 2006

haf said:
...Any suggestions on doing my own power flush as a short term fix eg stick a garden hose in the feeder tank and force water through?...

When I had this problem, I was told to put the mains onto the drain valve at the boiler, then open the drain valve and push the water into your system that way. This solved the problem for me except my downstairs rads arn't heating at all, but this may be due to the pipes from my boiler going into the first floor instead of the ground floor...

ChrisR · 1 Feb 2006

See "For Reference" section

haf · 1 Feb 2006

Thanks ChrisR, there is some good info in the reference section on how to mains flush the system so will give that a go at the weekend. Basic principle seems to be to block cold feed and vent pipe and then inject mains somewhere into the system (will look at my options around the pump area). and flush out..
Good news is i have a better quote for complete end-to-end replacement. BG said £5500 and a friend of a friend agreed to do the same for £3500 using same boiler etc... I'd rather pay a bit more and have it done properly by someone trustworthy....

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How to determine a faulty pump

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