Boiler losing pressure after each use

[belgianwaffle]

I have a Viessman Vitopend 100 combi boiler that loses .1 to .3 bar of pressure each time I turn off the heating (depending on how long it's been running).

I ran a short test the other day where I turned the heating on for only 5-10 seconds. I could hear the ignition and the water pump kick in. After I switched it off, the water pump continued running for another 5 minutes or so. But, the moment it stopped, the pressure immediately dropped by .1 bar.

Video (with sound): https://streamable.com/m23rk2

The heating works fine, but I have to refill the system every day to get the pressure back up to 1.5 bar.

We moved into the apartment only in September. We had our annual boiler maintenance in November and hadn't used the heating before that. Is it possible the technician forgot to tighten a valve somewhere?

 

[terryplumb]

Any water dripping from the PRV pipework,usually located exernally ?

 

[Johntheo5]

its normal for the pressure to fall by 0.1 to 0.3bar, 1m to 3m, when the pump stops, it should also rise by that amount when the pump starts but certainly doesn't account for the daily top ups, next time its topped up to 1.5bar, watch the pressure while the whole (rads) system heats up and see if the pressure approaches 3.0bar, if it does then the PRV, above, should start lifting and dumping water, sign of expansion valve requiring attention, possibly air end needs re charging or a failed diaphragm.

 

[belgianwaffle]

Any water dripping from the PRV pipework,usually located exernally ?

Where exactly should I be looking?

 

[belgianwaffle]

its normal for the pressure to fall by 0.1 to 0.3bar, 1m to 3m, when the pump stops, it should also rise by that amount when the pump starts but certainly doesn't account for the daily top ups

The pressure you see at the start of the video (around 1.6 bar) was like that before switching the heating on. Again, for the sake of the test, I ran it for only 5 seconds or so, then immediately switched it off. I did not notice it rise, but the drop was quite obvious.

next time its topped up to 1.5bar, watch the pressure while the whole (rads) system heats up and see if the pressure approaches 3.0bar, if it does then the PRV, above, should start lifting and dumping water, sign of expansion valve requiring attention, possibly air end needs re charging or a failed diaphragm.

I have already checked this. It never goes above 2.5 bar. :/

 

[terryplumb]

Where exactly should I be looking?

It's the white flexible hose on the right hand side that goes into the open
ended grey drain pipe .
Unfortunately that stupid design also takes the condensate from the boiler down that pipe ,so you can't tell if water from the PRV is coming down it as well.

 

[belgianwaffle]

I have also noticed that the shower water pressure fluctuates a lot and the water goes cold, and hot, and then cold again quite often and I can hear the boiler kick in every 15-20 seconds or so. Could both problems be related to the PRV?

 

[terryplumb]

I have also noticed that the shower water pressure fluctuates a lot and the water goes cold, and hot, and then cold again quite often and I can hear the boiler kick in every 15-20 seconds or so. Could both problems be related to the PRV?

No. Do other hot taps show the same symptoms ?

 

[Madrab]

Oh my, that's a proverbial minefield. I take it all that pipework runs into conduits that's are in concrete?

That being said, when the boiler clicks off it sounds like there is a slight release of pressure somewhere. When it does that can you see water being released down the grey pipe that the white pipe runs into?