Vaillant turbomax 242 pressure question

[wedge69]

Hello,

Just a quick (and hopefully simple) question - we don't have any problems with the boiler!

The pressure gauge of our Vaillant turbomax 242 reads at 1.0 bar as it is supposed to. When any hot water is called for the pressure drops to about 0.7 bar, and then flips straight back to 1.0 when the tap is turned off.

I always thought the pressure was that of the central heating system. How does calling for water affect this?

 

[Deleted member 105431]

when the pump is running (such as when running hot wter) the pressure gauge may fluctuate which is normal. (negative pressure created as gauge is just prior to pump)

 

[Agile]

Does this still happen if the power is turned off to the boiler?

Tony

 

[wedge69]

I can have a try of that if you want.

 

[wedge69]

Follow up:

I switched the power off to the boiler and opened a hot tap - the pressure did NOT drop.

So it only happens when the boiler is on, so I guess this links to the pump running as dangermouse mentioned.