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condensate pump not stopping (even when boiler off)

View the thread, titled "condensate pump not stopping (even when boiler off)" which is posted in Boiler Advice Forum on UK Plumbers Forums.

Hi guys,
I'm having this issue for a long time and I'm losing hope that it can be fixed so I'll welcome any advice or help in this matter.
Long story short:
We have Viessman Vitodens 100W 30KW Boiler installed in December 2022.
Since then we have constantly some issues with condensate pump but Viessmann engineers coming for annual maintenance say pump is not their problem, while company who installed the boiler send us to Viessmann engineers so it is vicious circle.
For first 2 years pump was activating pretty much every minute but then getting quiet. At some point it started running constantly (generating lots of noise and heat) until it completely broke down. I had to call local heating company to replace it, it was fine for a month and then problem happened again (pump running constantly). Local company came said that they have to 'alter wiring as whoever initially fitted pump when boiler was installed snipped off 2 core which kills power to boiler if pump fails'.
But problem still comes back from time to time (usually pump would run for over 12h, I'd get annoyed, cut the power off for day or two and then it would eventually stop) but this time it started on Thursday and still didn't go away (because it generates a lot of heat I had boiler off for most of the weekend as it wasn't really helping with heatwave but I was turning it on for bath/dishes and pump was still screaming).
I can call local company who helped few months ago but I feel like I'll pay for temporary solution while I really would like to solve this problem once and forever.
Here is video of pump running (as you can see turning boiler off makes no difference)


Here are details of the pump itself:
20250622_220215 (1).jpg

I'll be extremely grateful for any ideas where the problem is. Thank you!
 
Sounds like the pump isn’t able to pump anything maybe blocked outlet

Might be best to look where it terminates to

Also should be level left to right not sagging down to the right (you tried levelling it to see maybe if the float switch is getting stuck due to the angle ) ?
 
Thank you so so much! That's incredibly helpful! You are right, I checked with spirit level and pump is slightly wonky so I'll try to adjust it. In the meantime I emptied the pump and it eventually went quiet so that's incredible improvement! Thank you again, you are my hero!
 

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