High pressure on Vailant Ecoteck 831 boiler

[E17DIYer]

There is nothing going wrong with my system, but the pressure is regularly at 2.9 to 3.1 bar.

I bled all the radiators letting the air out and the system went down to 2.6. But having come back to the house after christmas it was 2.9 again.

i read that it should be between 1 - 1.5.

So i decided to bleed the top radiator in the loft a lot, and let lots of water out. Filled about a bucket. And the pressure fell down to 2.3.

I have a few questions


1 Why once all the air has been let out could there still be pressure in a closed central heating circuit? What is there providing the pressure?
2. How does removing water once there is no air left continue to reduce the pressure? Water can't be compressed?
3. Why is water still able to flow out of the system if there is nothing topping it up?

 

[CBW]

Check the filling loop is closed, if it is it could be letting by. Could be faulty pressure sensor. Does the pressure only rise with the heating on?

 

[E17DIYer]

Check the filling loop is closed, if it is it could be letting by. Could be faulty pressure sensor. Does the pressure only rise with the heating on?

It seems to gradually increase over time. Goes up a bit when heating on but not much. .1 or .2 bar. I suppose a more important question is what does it matter? Is there anything wrong with living at 3 bar?

 

[CBW]

It seems to gradually increase over time. Goes up a bit when heating on but not much. .1 or .2 bar. I suppose a more important question is what does it matter? Is there anything wrong with living at 3 bar?

It can stop the boiler working and operate the pressure relief valve, so although you won’t really notice it, it can be costly to put right. Sounds like sensor or loop letting by

 

[Johntheo5]

Its a 831, a combi boiler, maybe a leak in the plate heat exchanger causing the mains pressure (if higher that ~ 3.0 bar) to pressurize the primary side?.
Suggest reducing the pressure to say 2.0/2.5bar before going to bed and shutting off the mains supply to the combi and see if it remains at this pressure before firing up (CH) in the morning.