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Grundfos ups3 pump issue

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Steve Thackeray

Ups pump issue
Fairly recently, say 12 months ago, we had a new pump fitted.
It's a grundfos ups3 15- 50/65 130.
(We have a small expansion tank next to the large tank in the loft. So not a sealed system)
After it runs normally for several hours it just stops working. The radiators obviously go cold. But if you turn the timer off and turn it back on again the pump immediately starts working again and radiators warm up. It shows one green light and two Amber ones. I believe that's performance curve 3. Also occasionally I see water coming out of one of the overlow pipes coming out the side of the building.
This problem doesn't happen all the time but it's fairly often. We only know, when it suddenly goes cold in the lounge. Is this a simple issue which I could solve as a keen diyer, or do i need a professional plumber.
Next time it stops working after several hours and assuming its still getting a call from the programmer/roomstat or cylinderstat check for mains voltage at the pump or at the pump cable JB.

Its no wonder you are getting vent pumpover ets running it on CC3, these are a very powerful pump and will pump up to 1.15m3/hr at a 6.4M head, or 2.2m3/hr at a 4M head, they also have strange CC ( constant curve) charasteristics in that they behave in constant pressure, CP fashion for much of their time, don't know why, and never did find out. A 3M head should generally satisfy most installations and should stop that pump over so suggest CP1 or even PP2 which although a bit mean on head might well satisfy your requirements, you might give them a go.

Wouldn’t say the pump was at fault room
Stat would be my guess

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