New Grundfos slow to start after 2 weeks, replacement did the same...

[Thandar]

Open-vented system, horizontal pump, had a problem with the old pump, engineer replaced it with new Grundfos.
2 Weeks later, when it started up loud banging followed by a loud whoosh after 2 minutes
The boiler was kettling as the pump wasn't running, but the light is on, then after a bit the pump finally kicks into life
They come back and replace the head, works for 2 weeks and then it does the same thing again
The system has been drained 3 times and everything checked, they've tried everything but the problem remains
Any idea why it's not starting straight away?

 

[gasmanstu72]

what pump is it?
if its the new(ish) Alpha 2 pump make sure the wire is hanging down and you can read the display without tilting your head 90 degrees, a lot of people fit them on the horizontal but don't move the head, this will cause air to be trapped and the boiler to overheat

 

[D_Hailsham]

if its the new(ish) Alpha 2 pump make sure the wire is hanging down and you can read the display without tilting your head 90 degrees, a lot of people fit them on the horizontal but don't move the head, this will cause air to be trapped and the boiler to overheat

That's contrary to the installation instructions which say the cable entry can be in any position except on the top. Have Grundfos confirmed this is a problem?

 

[ScottishGasMan]

horizontal pump

Got a picture with the position of the pump?

Alpha 2 pump make sure the wire is hanging down and you can read the display without tilting your head 90 degrees, a lot of people fit them on the horizontal but don't move the head, this will cause air to be trapped and the boiler to overheat

No it wont. As long as the orientation of the body is correct it will vent as good as it can (which is not very good) the pump head has no relavance to the ability to remove air. The only reason they dont advise fitting the head with the wire up the way is strain relief for the cable. And yes the instructions will also confirm any of the positions apart from cable leaving out the top is fine.


When the systems been drained, did you see the colour/quality of the water? Any recent new pipework added to or replaced on the system? has any cleaning soloution been run through the system in the last 6 months?

Personaly if I suspected a sticking pump like yours, I would not have swapped the head, I'd have changed the full thing again, incase there is a defect in the casting of the pump body fouling the impellor slighly

 

[Thandar]

Wow, wasn't expecting so many replies
It's a UPS2 not Alpha, and it's tilted up by 15-20 degrees from flat, which seems to be in keeping with their recommendations for a horizontal setup.
They didn't replace the body the second time as it's in a tricky spot and very difficult to wedge in....but might be worth doing!
I should also say it only does this if it's been off for a while, over 2 hours really, and also the green light comes on straight away on the pump, it just doesn't fire for a few minutes.
The water was clear when they drained it and they put in cleaning solution, no new pipework since I've been there (5 years).
I'll see if I can get a picture when I get home

 

[ScottishGasMan]

it and they put in cleaning solution,

So your saying they have put in cleaning solution?

If that's the case it needs very thoroughly flushing out, you can put in cleaners into a system and just leave it, and certain cleaners are know for there ability to damage pump heads!

 

[IKJ]

I don't do much on the installation side, mostly just repairs but have personally replaced 4 new Grundfos pumps in just a year, the pumps with the suppresor leads seem to be the worst, but have heard others say that the newer 15/50-60 pumps have let them down too, one guy had a big argument with the Grundfos reps at our local merchants, as no recompense has been offered for our time, although the pumps are being supplied foc.

 

[ScottishGasMan]

I don't do much on the installation side, mostly just repairs but have personally replaced 4 new Grundfos pumps in just a year, the pumps with the suppresor leads seem to be the worst, but have heard others say that the newer 15/50-60 pumps have let them down too, one guy had a big argument with the Grundfos reps at our local merchants, as no recompense has been offered for our time, although the pumps are being supplied foc.

Yea, hav enot had first hand dealings but heard a number of people having issues with the UPS a while ago, the Alpha heads seem fine, but thought the UPS thing was sorted out a while ago, maybe not

 

[Thandar]

It's been drained twice since then and had a second pump installed, I'll check what cleaner it was as the bottle is still by the tank

 

[ScottishGasMan]

Yea, please let us know

 

[D_Hailsham]

It's a UPS2 not Alpha, and it's tilted up by 15-20 degrees from flat, which seems to be in keeping with their recommendations for a horizontal setup.

The instructions say the pump must be installed with the shaft horizontal; no mention of 15-20 degrees from the flat. Is it under a floor?

Is it an unvented system with a F&E tank in the loft? If so, what is the vertical distance between tank bottom and pump?

A pic would be very useful.

 

[Thandar]

I was worried about the tilt as well but the manual does say it's OK at a slight upward angle, but not down....
The tank is in the loft so 1 floor up from the pump and 2 up from the boiler

 

[D_Hailsham]

I was worried about the tilt as well but the manual does say it's OK at a slight upward angle, but not down....
The tank is in the loft so 1 floor up from the pump and 2 up from the boiler

I know that, in the past, Grundfos said that it was OK for the front to be slightly higher so I check the latest versions of the manuals on their website. The Installation Instructions say:The pump must always be installed with horizontal motor shaft.

The tank position is high enough above the pump to ensure no cavitation. Have you checked if any water comes out of the vent pipe (the one hanging over the F&E tank)?

 

[gasmanstu72]

Alpha 2 pump make sure the wire is hanging down and you can read the display without tilting your head 90 degrees, a lot of people fit them on the horizontal but don't move the head, this will cause air to be trapped and the boiler to overheat

No it wont. As long as the orientation of the body is correct it will vent as good as it can (which is not very good) the pump head has no relavance to the ability to remove air.

i have had terrible trouble getting the air out of these pumps, flow switches, and overheat stats on boilers, ive always found that turning the body so that the cable is facing down has made a massive difference. turn it up to III and the air clears much better.

 

[Thandar]

OK, back home, and as promised here are the pics
First one shows how tight it is in there
Second shows the pump angle
Third is the Chenral Heating Cleaner bottle

Also I checked the F&E tank and it's definitley has some water in there, it's slightly warmer than the cold tank, but may have come through expansion pipe rather than overflow, the water up there is not nice, and there is a lot of sedement at the bottom...
And listning to it try to start up you can hear it try, and once when the boiler was running, there was a very nasty noise (bag of spanners) that sounded like it was from the pump, then about 10 seconds later the pump started and everything was fine again