Vaillant ecoTech exclusive pump overrun

[Cez44]

I wonder if someone could help. I have Vaillant ecoTech exclusive combiboiler just installed. It seems to be working fine but whenever I open any cold water tap or even flush the toilet, the boiler starts for 30-40 sec. without the burner actually on. The message on the display is "HW pump overrun". I wonder if this is a fault and what could be the cause.
I would be grateful for advice.
Cez44

 

[mickyg]

dead leg in the hot water pipework. Speak to your installer about locating and removing the problem.

 

[Cez44]

dead leg in the hot water pipework. Speak to your installer about locating and removing the problem.

Thanks for a prompt answer. Is this situation potentially harmful for the boiler? And forgive my ignorance what actally is a dead led?
Cez44

 

[mickyg]

not really harmful, apart from increasing component wear. A dead leg is a redundant length of pipework thats still connected to the system. Its quite common to have these after combi conversions, but the installer should always remove them where possible to prevent this problem you have.

 

[kevplumb]

it fills with air and the water compresses it when you flush the compressed air pushes the water out

and the boiler thinks a hot tap is open

when the pressure levels out the air gets compressed again

and so on and on and on

 

[Agile]

Eventually the air usually dissolves but that can take several weeks.

O² dissolves quickly but the N takes a long time.

Tony

 

[Cez44]

Thanks everybody! Now it all makes sense.
Cez44