Vaillant Ecotec pro 24 - F75

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Hello,

Hoping someone can help.

I've got a vaillant boiler for water and heating in an outbuilding, it's only 2 years old but hasn't been used at all in the last year.

Upon turning on, you can hear a faint noise, like something is trying to activate, this is from the lower section, around the diverter/motor area, it's just a hum but not like a motor trying to turn.

After a few tries, I get the F75 error. Pressure is spot on.

I pulled the pressure sensor plug and it does lose the pressure on the LCD and throw another error, so that told me that the sensor is ok. I did also remove it and it was a bit black, gave it a clean and popped it back. No joy.

I turned the boiler back on and decided to add more pressure while it was trying, to trick it to think there was flow and it started! Pump was going and temp going up on the gauge, but as soon as I stopped filling it, the boiler stopped.

Does this offer any clues to what my issue is?

Cheers!
 
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CBW

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It means that there’s an issue with a communication between the pump and low after pressure sensor and you could have a dirty system. Removing the cover on that boiler forms part of the combustion circuit and should be checked for safety afterwards.
 
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Its quite likely IMO that the circ pump is "stuck" as there will be a slight rise in pressure when it starts, if it doesn't, F75 is annunciated, the reason it started while topping up was it saw this as a pump start/run?.

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